Cardiology I – A Review of Cardiovascular Anatomy and Physiology
Upon completion of this course, the student will be able to:
1. Identify the basic anatomy of the cardiovascular system.
2. Describe basic principles of cardiovascular physiology.
3. Describe basic principles of cardiac electrophysiology.
4. Identify the following information concerning example cases of cardiovascular dysfunction:
-Typical Patient Presentation.
-Key Elements of the History and Physical Exam.
-Basic Pathophysiology.
-Initial Patient Assessment and Management.
Case Studies:
1. Cardiac Tamponade.
2. Cocaine Overdose.
3. Hemorrhagic Shock.
Vocabulary
Perfusion - The flow of blood through the lumen of a vessel.
Blood Pressure - The tension of blood within the arteries.
Automaticity - Characterized by independence from central nervous system control. Enables the heart to produce action potentials.
Hypertrophy - Growth of muscle tissue secondary to increased work.
Tamponade - Compression of the heart resulting from an increased volume of fluid in the pericardial sac.

Diastole - Period of the heart cycle characterized by filling of the ventricles with blood.
Shock - A condition characterized by failure of the circulatory system to maintain adequate perfusion of vital organs.
Systole - The phase of the cardiac cycle characterized by contraction.
Depolarization - Characterized by a change in polarity.
Beta-receptor - A receptor which, when stimulated, increases heart rate and contractility, as well as dilates the bronchial tree and vascular smooth muscle.
Action Potential - The change in the electrical potential of a membrane that occurs when a nerve or muscle cell is excited.
Contractility - The ability of a muscle fiber to shorten or increase its tension.
The cardiovascular system is one of the most important organ systems in the human body. It consists of a pump (the heart), a series of highways (the vessels), and a vehicle (the blood). The primary function of this system is to transport nutrients and oxygen to the tissues of the body. This function is made possible, in part, by the complex structure and physiology of the heart, which enables it to beat at a regular rate and rhythm several billion times in a person’s life.
Despite the impressive durability of the cardiovascular system, there are a number of processes that can lead to cardiovascular compromise and death. In fact, cardiovascular disease is the underlying cause in 36.3% of all deaths each year. Moreover, cardiovascular disease has been the leading cause of death in America every year since 1900, except for 1918.
1
As an EMT, you will be at the forefront of treating and transporting persons suffering from imminently life threatening cardiac conditions and can play an integral role in saving countless lives. Therefore, it is imperative that you have a solid working knowledge of the anatomy and physiology of the cardiovascular system so that you can more effectively assess and manage these patients.
The following course will begin by describing the anatomy and physiology of the cardiovascular system. After that, basic principles of cardiac electrophysiology will be detailed.
The course will conclude with a presentation of three cardiovascular case studies that will demonstrate how increasing your knowledge of cardiac anatomy and physiology can help you provide even more effective care to your patients.

The Location of the Heart:
The heart, which is about the size of a small fist, is located in the center of the chest, just behind the sternum. Other important structures, which border the heart, include: the diaphragm
(located just below the heart), the aorta (just above the heart), the esophagus and vertebral column (just behind the heart), as well as the lungs (on either side of the heart).
The Tissue Layers of the Heart:
The heart is composed of three tissue layers – the pericardium, myocardium, and endocardium.
-The Pericardium:
The pericardium is the outermost layer of the heart and serves as a protective barrier. This layer is divided into the parietal pericardium and visceral pericardium. The parietal pericardium is composed of a thick layer of fibrous tissue and encases the heart, while the visceral pericardium is composed of a thinner cell layer and is adherent to the heart itself. A space exists between the visceral and parietal pericardial layers, which holds a small amount of fluid. This fluid serves as a lubricant and decreases friction between the beating heart and surrounding structures. The pericardial space can also collect fluid, from medical disease or trauma, which can result in life threatening cardiac tamponade and death.
-The Myocardium:
The middle layer of the heart is the myocardium, which is composed of thick muscular tissue. The myocardial cells, which make up this layer, are similar to skeletal muscle cells but are more complex because they can transmit electrical signals.
-The Endocardium:

blood.
The innermost most layer of the heart, known as the endocardium, is in contact with the
The Chambers of the Heart:
The heart is basically a four-chambered box, consisting of two upper chambers (the atria) and two lower chambers (the ventricles).
-The Atria:
The atria are thin-walled structures that receive blood from the circulation and pump it into the ventricles. The right atrium receives deoxygenated blood from the body via the inferior and superior vena cavae and empties into the right ventricle. The left atrium receives oxygenated blood from the lungs via the pulmonary veins and empties the blood into the left ventricle.
-The Ventricles:
The ventricles, which have thick, muscular walls, are responsible for generating the contractile force that pumps blood throughout the body. The right ventricle receives deoxygenated blood from the right atrium and pumps it through the pulmonary artery and into the lungs. The left ventricle receives oxygenated blood from the left atrium and pumps it through the aorta and into the vessels that supply the rest of the body. The walls of the left ventricle are considerably thicker than the right ventricle secondary to hypertrophy , which occurs in response to the left ventricle having to pump against higher pressures.
-The Septa:
The right and left chambers of the heart are separated from each other by a layer of tissue known as a septum. The atria are separated from each other by the interatrial septum. Similarly, the ventricles are divided by a layer of tissue called the interventricular septum. In addition to acting as a barrier between the right and left ventricles, the interventricular septum contains conductive tissue that aids in the electrical stimulation of the heart.

The Heart Valves:
The heart has four valves – two atrioventricular valves and two semilunar valves.
-The Atrioventricular Valves:
The valves which control the flow of blood between the atria and ventricles are known as the atrioventricular valves. The right atrioventricular valve is called the tricuspid valve and is named as such because the valve is composed of three leaflets (as the name tri – cusp – id implies). The left atrioventricular valve is called the mitral valve and is composed of only two leaflets.
The atrioventricular valves themselves are connected to fibrous tissues called chordae tendineae, which are attached to specialized papillary muscles in the ventricles. The chordae tendineae and papillary muscles function to keep hold of the structural integrity of the valves and prevent them from prolapsing into the atria, which would lead to backflow of blood.
-The Semilunar Valves:
The semilunar valves permit one way movement of blood between the ventricles and the great arteries. The right semilunar valve, also known as the pulmonic valve, connects the right ventricle to the pulmonary artery. The left semilunar valve, known as the aortic valve, allows oxygenated blood to flow from the left ventricle to the aorta.

Introduction:
All of the cells in our body require a constant supply of oxygen and nutrients in order to function. This supply of oxygen and nutrients is provided by the constant passage of blood through the vessels, which is known as perfusion.
Structure:
Blood vessels are made up of a vessel wall, which surrounds a lumen (or opening).
Most vessel walls are made up of three layers of cells, with the exception of the capillaries, which consist of a single layer of cells. The innermost lining of a blood vessel is known as the intima, which is composed of a very thin layer of cells. The next layer is called the media, which consists of elastic fibers and muscle fibers. The media gives vessels their contractile properties and strength. Due to increased strain, the media of an artery is much thicker than the media of a vein. The outermost layer of a vessel is called the adventitia, which

serves as a dense fibrous covering. It gives the vessel the strength to withstand the pressures generated by the heart’s contractile force.
The size of the central opening (or lumen) varies considerably among the different types of vessels and is directly related to the amount of blood that can be transported – the larger the diameter of the vessel, the greater the flow of blood.
There are two main types of blood vessels. They are differentiated based on the oxygen status of the blood they carry. In general, vessels that carry oxygenated blood are known as arteries, whereas vessels that carry deoxygenated blood are known as veins.
****NOTE: The pulmonary vasculature is an exception to this rule. The pulmonary artery transports deoxygenated blood to the lungs, whereas the pulmonary vein transports oxygenated blood to the heart.
The Arterial System:
The arterial system, which functions at very high pressures, carries oxygenated blood away from the heart.
The largest vessels in this system are called arteries. The arteries branch into smaller vessels called arterioles. The arterioles divide into smaller, single-walled vessels called capillaries, which act as connecting points between the arterial and venous systems. The exchange of gases, fluids, nutrients, and waste products occurs through the very thin capillary walls.
The Venous System:
The venous system transports deoxygenated blood from the peripheral circulation back to the heart. It functions under much lower pressure than the arterial system and, consequently, these vessels have much thinner walls.
Blood enters the venous system through capillaries, which drain into larger venules. The venules then drain into thicker-walled veins. These veins then drain into the vena cavae. As previously stated, the vena cavae empty into the right atrium.
The blood traveling from the capillaries to the venules and back to the heart is under very low pressure. To facilitate the return of blood to the heart, the vessels of the venous system contain one-way valves to prevent the back flow of slow moving blood. Furthermore, the contractions of muscles, which are near veins, function to “squeeze” blood back to the heart.
This system is highly coordinated such that you do not feel pulsations through the veins; rather, the blood flow through veins is slow and steady.

The Great Arteries:
-The Vena Cavae:
The superior and inferior vena cavae deliver deoxygenated blood directly to the right atrium of the heart. The superior vena cava delivers deoxygenated blood from the head, neck, and upper extremities. The inferior vena cava delivers deoxygenated blood from tissues located below the level of the heart. From the right atrium, the blood then flows into the right ventricle.
-The Pulmonary Artery and Pulmonary Veins:
From the right ventricle, the deoxygenated blood is pumped through the pulmonic valve and into the pulmonary artery. The pulmonary artery delivers blood to the lungs. After becoming oxygenated in the lungs, the blood passes through the pulmonary veins and enters the left atrium.
This oxygen-rich blood then flows from the left atrium through the mitral valve and into the left ventricle.
-The Aorta:
The left ventricle then pumps the blood through the aortic valve, into the aorta, and out to the peripheral circulation.
The aorta is given several different names as it courses through the chest and abdomen.
The ascending aorta is the first segment of the aorta. It arises directly from the heart and ends at the aortic arch. The aortic arch is the “U” shaped portion of the aorta and signifies the point where the aorta transitions from ascending to descending. The descending aorta is given two names – the thoracic aorta and the abdominal aorta. The thoracic aorta extends from the aortic arch to the diaphragm. Once the aorta travels below the diaphragm and into the abdomen, it is classified as the abdominal aorta.
The Coronary Arteries:
The coronary arteries supply the heart with oxygen and nutrients. They branch off the ascending aorta, just above the aortic valve. The major coronary vessels are located on the surface of the heart and feed small arteries that penetrate the myocardium.
The coronary vessels are constricted when the heart is contracting; therefore, blood mainly flows through the coronary vessels when the heart is in diastole (also known as the period of time when the heart is relaxed and is filling with blood).
The right coronary artery wraps from front to back around the heart and branches off into the posterior descending artery and the marginal artery. The right coronary artery primarily supplies the right atrium, the right ventricle, and part of the heart’s conduction system.

The left coronary artery is located anteriorly on the heart’s surface and branches into the anterior descending artery and the circumflex artery. The left coronary artery supplies the left ventricle, part of the right ventricle, the interventricular septum, and a portion of the heart’s conduction system.
Just as in the rest of the circulatory system, veins carry deoxygenated blood away from the heart. Deoxygenated blood from the left coronary arteries enters the anterior great cardiac and lateral marginal veins and empties into the coronary sinus. The right coronary system empties into the right coronary vein, which then drains directly into the right atrium.
Although the heart is supplied primarily by the right and left coronary vessels, there are also very important anastamoses (or communication points between two or more vessels) among the various branches of the coronary arteries that allows for collateral circulation. Collateral circulation is an important protective mechanism that provides alternative pathways for blood to flow in the event that there is a blockage in any part of the system.

The most important function of the cardiovascular system is to supply the tissues of the body with oxygen and nutrients. Any disruption of this process can result in tissue dysfunction.
Therefore, it is important that you have a solid working knowledge of normal cardiovascular physiology, so that you can better understand how alterations in circulatory function may affect a patient.
The following are some basic definitions pertaining to cardiovascular physiology that you may hear being used around the ED, as well as by your patients.
Basic Definitions Pertaining to Cardiovascular Physiology:
-Ejection Fraction: Is the ratio of the amount of blood ejected from the left ventricle to the amount of blood contained in the left ventricle immediately prior to contraction.
-A healthy heart ejects around two thirds of the blood that is present in the ventricles at the end of filling (known as diastole).
-Stroke Volume: Is the volume of blood ejected by the heart with one contraction.
-There are three factors that affect the heart’s stroke volume – preload, contractility , and afterload.
-Preload: Refers to the amount of blood that fills the ventricles during diastole.
-The more blood that returns to the heart, the more that must be pumped out. The venous system volume can be contracted or expanded to return more or less blood to the heart in order to meet the demands of the body.
-Contractility: Refers to the contractile strength of the heart.
-Contractility is influenced by preload and nervous system stimulation. As the preload increases, the ventricular muscle becomes increasingly stretched, which leads to the generation of a stronger ventricular contraction. This phenomenon is known as Starling’s Law of the heart. However, this stretch-induced increase in contractility has its limits. If preload volume becomes too great, the contractility of the heart will decrease as muscle fibers are stretched to their limits. In addition to preload, nervous system stimulation can increase or decrease the contractile force of the heart.
-Afterload: Refers to the resistance against which the ventricles must pump.

-Afterload is essentially determined by the peripheral vascular resistance. The pressure generated by the contractile force of the heart must exceed the resistance of the peripheral vasculature in order for the heart to pump blood out into the periphery. An increase in the peripheral vascular resistance will decrease the stroke volume. Conversely, a decrease in the peripheral vascular resistance will increase the stroke volume.
-Cardiac Output: Is the amount of blood that can be pumped by the heart in one minute.
-The cardiac output is calculated by the stroke volume multiplied by the heart rate. This equation highlights that heart rate, preload, afterload, and contractility can affect the cardiac output.
Blood Pressure: Is the tension the blood exerts on the walls of the arteries.
Blood pressure is determined by cardiac output and peripheral vascular resistance.
Peripheral vascular resistance increases when vessels constrict and decreases when vessels dilate.
The right atrium receives deoxygenated blood from the body via the superior and inferior vena cavae. The deoxygenated blood from right atrium flows through the tricuspid valve into the right ventricle. From the right ventricle, the deoxygenated blood is pumped through the pulmonic valve into the pulmonary artery and out to the lungs. After being oxygenated in the lungs, the blood is sent through the pulmonary veins into the left atrium. This oxygen-rich blood then flows from the left atrium through the mitral valve and into the left ventricle. It is then pumped through the aortic valve into the aorta and out to the peripheral circulation. Finally, blood is returned from the peripheral circulation to the right atrium, and the cycle continues.

The cardiac cycle is defined as the events that occur between one heart contraction and the next. This cycle is divided into two phases – relaxation and contraction. The relaxation phase of the cardiac cycle is known as diastole and is characterized by filling of the ventricles. The second part of the cardiac cycle is known as systole.
During systole, the heart contracts and forces blood into the aorta and pulmonary artery.
Diastole begins with the closing of the semilunar valves and the opening of the atrioventricular valves. This allows the pressure in the ventricles to become low enough to allow blood to enter from the atria. Towards the end of diastole, the atria give a quick contraction to finish emptying blood into the ventricles. This is known as the “atrial kick” and helps to boost cardiac output. Next, the ventricles receive a stimulus to contract, which increases intraventricular pressure. This increased pressure forces the mitral and tricuspid valves to close, and opens the semilunar valves to allow blood to flow out to the pulmonary and systemic circulations. When the pressure in the pulmonary artery and aorta overcomes the pressure in the

ventricles, the semilunar valves close, and the atrioventricular valves open, marking the beginning of diastole and the start of a new cardiac cycle.
Introduction:
The heart is controlled by two opposing divisions of the autonomic nervous system – the sympathetic and parasympathetic nervous systems. These two systems will ideally balance each other out and create a steady state. However, during stressful situations the sympathetic nervous system dominates, which leads to tachycardia, increased cardiac output, and increased oxygen demand of the heart. Conversely, during relaxed states, such as sleep, the parasympathetic nervous system predominates, which leads to the resting heart rate, baseline cardiac output, and decreased oxygen demand of the heart.
The Sympathetic Nervous System:
The sympathetic innervation of the heart consists of nerves that arise from the thoracic and lumbar spine and synapse (or connect) with the nervous tissue of the heart, which is known as the cardiac plexus. The nerves of the cardiac plexus serve as a conduit through which certain neurotransmitters (such as norepinephrine and acetylcholine) can travel to reach their target receptors in the heart. The target receptor for the sympathetic nervous system in the heart is the
Beta-1-receptor.
This receptor is responsible for increasing the heart’s rate and contractility.
When referring to the sympathetic nervous system, the term “adrenergic,” may be used.
This term refers to the nerve cells or fibers of the autonomic nervous system that employ norepinephrine as their neurotransmitter. Since norepinephrine is used exclusively in the sympathetic nervous system, one can see how “adrenergic” also implies “sympathetic.”
The Parasympathetic Nervous System:
The parasympathetic nervous system exerts its control on the heart through the vagus nerve, which originates from the brainstem as cranial nerve ten. The vagus fibers connect to the atria and the superior portions of the ventricles. The release of neurotransmitters from the vagus nerve results in a decrease in heart rate and contractility.
When referring to the parasympathetic nervous system, the term, “cholinergic” is often used. This word refers to nerve cells or fibers that employ acetylcholine as their neurotransmitter.
The heart contracts in a synchronized manner several billion times in a person’s life.
Fortunately, a person does not need to intentionally instruct his or her heart to beat. Rather, the

heart can spontaneously generate its own electrical signals, which can then be propagated throughout the cardiac muscle tissue to produce contractions.
Introduction:
The spontaneous generation of cardiac electrical signals, as well as their propagation, is due to alterations in electrolyte concentrations. The major electrolytes that are involved in this process include: Sodium, Calcium, Potassium, Magnesium, and Chloride.
Sodium:
Sodium plays a vital role in automaticity , which is a property characterized by the heart’s ability to generate spontaneous, repetitive contraction stimuli.
Calcium:
Calcium is also essential for automaticity and, in addition, plays a vital role in cardiac contractions.
Potassium:
Potassium’s role in the heart is to reset the repetitive firing system so that it can quickly become active after each electrical stimulus it generates.
Magnesium and Chloride:
The roles of Magnesium and Chloride are unclear, but low levels of these electrolytes impair the replacement and functioning of Sodium, Calcium, and Potassium, thus altering overall heart activity.
The Importance of Proper Electrolyte Concentration Balance:
Balance of the concentrations of electrolytes is important, as either an increase or decrease in electrolyte levels can alter the function of the heart. For example, hypercalcemia (or too much calcium) can result in increased cardiac contractility, while hypocalcemia (or too little calcium) can depress the contractility of the heart and cause electrical irritability. As another example, hyperkalemia (or too much potassium) decreases the automaticity and conduction of the heart, while hypokalemia (or too little potassium) can increase electrical irritability of the heart.

Introduction:
Automaticity of the heart is produced by spontaneous and repetitive depolarization of certain cardiac cells, known as pacemaker cells. The depolarization of these cells leads to the generation of action potentials, which are electrical signals that are propagated throughout the cardiac muscle tissue and result in contractions. Understanding depolarization is essential to comprehending cardiac electrophysiology as a whole.
Depolarization:
-Introduction:
The process of depolarization occurs at the cellular level and involves changes in the electrical environment of a cell. This electrical environment is determined by the difference in the concentrations of charged particles between the inside and outside of the cell.
-Resting Membrane Potential:
At rest, the inside of a myocardial cell has a charge that is more negative than its surroundings. Therefore, the cell is said to have a negative resting membrane potential. This potential is normally around -90 millivolts, meaning the charge inside the cell is 90 millivolts lower than the surrounding environment.
-Anions and Cations: The resting membrane potential is the result of a difference in the concentration of cations (which are particles with a positive charge) and anions (which are particles with a negative charge) between the inside of the cell and the outside of the cell. The two most abundant charged particles within a cell are proteins (which have a negative charge) and the positively charged Potassium ion (K
+
). The most abundant charged particles located outside of a cell are the positively charged Sodium ion (Na
+
), and the positively charged
Calcium ion (Ca
+
).

-Creation of the Negative Resting Membrane Potential:
The unbalanced distribution of particles on either side of the cell membrane is maintained by passive diffusion (across a selectively permeable membrane), as well as by active diffusion
(which involves specialized membrane pumps). Passive diffusion as you may remember is a force that tends to move particles from areas of higher concentration to areas of lower concentrations so as to achieve equilibrium. Selective permeability means that a membrane will allow certain particles to easily pass, while it may restrict passage of other particles. Active diffusion establishes concentration gradients through the use of energy-requiring membranebound pumps.
-Passive Diffusion: Due to the high concentration of Potassium ions inside a cardiac cell, a concentration gradient exists that leads to the passive diffusion of Potassium ions out of the cell. This concentration gradient, however, is balanced by the negative electrical gradient
(created by the intracellular protein anions) that tends to pull the positively charged
Potassium ions back into the cell. At a certain electrical charge, these two forces tend to balance out. This is known as the Potassium resting membrane potential.
Similarly, Sodium ions are present in large concentrations outside the cell and will tend to diffuse into the cell. However, at rest, the cell membrane is relatively impermeable to
Sodium and, therefore, Sodium ions remain in high concentrations outside the myocardial cell. Consequently, a Sodium resting membrane potential is created.
-Active Diffusion: Membrane potentials are not purely determined by passive concentration gradients and electrical forces; they are also determined by processes involving the active diffusion of ions. One such process involves the Sodium/Potassium pump, which is, perhaps, the most physiologically important pump in our body. It exports three Sodium ions out of the cell in exchange for pumping two Potassium ions into the cell. This results in maintaining
Potassium at high concentrations within a cell, as well as maintaining Sodium at high concentrations outside the cell. In addition, due to the three positive charges being pumped out of a cell for every two positive charges pumped in, there is a net efflux of positive charge from the cell.
Since a cell membrane is relatively permeable to both the Sodium and Potassium ions
(whether by active or passive diffusion), a resting membrane potential will exist that falls between the individual Sodium and Potassium resting membrane potentials.
-Depolarization and the Generation of an Action Potential:
As mentioned, at a steady state, the inside of a cardiac cell has a negative charge, while the outside of the cell has a positive charge. This difference in charge normally measures around
-90 millivolts in a myocardial cell. If a myocardial cell remains at this negative value, then it will

not contract. However, if something causes the inside of the cell to become more positive, a myocardial contraction may be produced.
As mentioned in the introductory paragraph, certain myocardial cells are capable of spontaneous and repetitive depolarization. These cells, known as pacemaker cells, have unstable resting potentials, which are caused by a slow influx of positive Sodium and Calcium ions while at rest. As the cell slowly depolarizes, it reaches a point at which a rapid alteration in the permeability of the membrane will occur. Once this happens, positive charges (from Sodium and
Calcium) flood the cells and produce an action potential. This action potential then leads to contraction of cardiac muscle fibers.
After an action potential is generated, the cell quickly returns to its resting membrane potential. Positive ions then begin to leak into the pacemaker cell again. This will lead to another action potential and, therefore, the repetitive firing cycle continues.
Introduction:
The cardiac conduction system is responsible for the organized transmission of electrical impulses in the heart. This system consists of a network of cells that transmits electrical potentials from the atria to the ventricles.
The Conduction Circuit:
The sinoatrial node, which is located in the right atrium, is responsible for the generation of electrical impulses. These impulses are then transmitted through atrial conduction tissue to the atrioventricular node. The atrioventricular node causes a slight delay in transmission, and then allows the signals to travel to the cells of the interventricular septum. The conduction fibers in the interventricular septum are known as the bundle of His. These fibers divide into the left and right bundle branches, which transmit electrical impulses to the left and right ventricles, respectively.
Properties of the Conduction System:
The ability of the conduction system to stimulate the heart to contract in an organized fashion stems from its intrinsic properties. These properties include: excitability, conductivity, and automaticity.
-Excitability: Refers to the ability of a cell to respond to an electrical stimulus.
-Conductivity: Refers to the ability of each cell of the conduction system to conduct individual electrical impulses from one cell to another.

-Automaticity: Refers to an individual cell’s ability to “self-excite” without any impulse from an outside source.
The conductive tissue that has the fastest automaticity acts as the pacemaker of the heart.
In a normal heart, the sinoatrial node has the highest automaticity and, thus, acts as the primary pacemaker of the heart. However, if one pacemaker in the heart fails to act, the conduction tissue with the next fastest rate will gain control of the pacing function. Each component of the conductive system has its own intrinsic rate of self-excitation, as follows:
-The sinoatrial node has an intrinsic rate of 60-100 beats per minute.
-The atrioventricular node has an intrinsic rate of 40-60 beats per minute.
-The ventricular conduction tracts have an intrinsic rate of 15-40 beats per minute.
2,3
Introduction:
Once the electrical signal has been generated in the pacemaker cells, and has propagated through the cardiac conduction system, it is then very rapidly transmitted from one myocardial cell to the next so as to achieve a synchronized contraction.

The Intercalated Disc:
The electrical signal is able to pass quickly among the myocardial cells due to a unique structural component of cardiac cells known as the intercalated disc. Intercalated discs are specialized junctions that exist between myocardial cells, which function to increase the rate at which action potentials can be spread from cell to cell.
The Contraction of the Heart as a Coordinated Unit:
Due to this rapid spread of action potentials, cardiac muscle is able to function and contract as a coordinated unit. This coordinated unit of contraction is known as a syncytium and allows the heart to function according to an “all or nothing” principle. That is, if a single muscle fiber is depolarized, the action potential will spread throughout the entire syncytium and the whole area will contract.
The heart is composed of two syncytia, the atrial syncytium and the ventricular syncytium. The two syncytia are separated by dense fibrous tissue that allows them to act independently. The atrial syncytium contracts from superior to inferior, allowing the atria to function as a unit and squeeze blood into the ventricles. The ventricular syncytium contracts from inferior to superior, so as to push blood into the circulation.
A 24 year old woman calls 911 and reports that her 15 year old brother has been shot while caught in the crossfire of a gang gun battle.
You arrive on the scene within 2 minutes and find a young male with a gunshot entry wound to the left side of his chest. The young man is no longer talking, but he is still breathing.

He is sweaty and is clutching his chest. From brief questioning of the patient’s sister, you learn that the young man has had no previous medical problems and leads an active healthy life.
Physical examination reveals distended neck veins and muffled heart tones. You cannot palpate a blood pressure. The patient is deteriorating rapidly.
-The Patient History:
1) The patient’s sister states that the young man has no medical problems and leads an active lifestyle. This historical information is useful because you can expect that the patient’s cardiovascular anatomy will be normal.
2) The patient has been shot in the left chest, which means the patient may be suffering from a penetrating injury to the heart, lungs, or major blood vessels in the chest.
3) Despite arriving within 2 minutes of the incident, the patient’s condition is beginning to deteriorate rapidly, which helps us know that there is an acute process causing the patient to clinically worsen.
-The Physical Exam:
1) The patient’s neck veins are prominent, his heart sounds are difficult to hear, and you cannot measure his blood pressure. These three findings are known as Beck’s Triad, which consists of three clinical signs (hypotension, muffled heart tones, and distended neck veins) that occur in association with cardiac tamponade.
Cardiac tamponade refers to a condition in which the space between the layers of the pericardium becomes filled with fluid or blood. Initially the right ventricle will collapse and be pushed over against the left ventricle until the whole heart is compressed by the pericardial fluid.
The collapse of the ventricles causes cardiac dysfunction and imminent death if interventions are not performed to quickly drain the fluid from around the heart.
-See figures that follow.

A concerned 16 year old female calls the EMS and states that her boyfriend has overdosed on cocaine. She reports that they went to a party, and her boyfriend, who has never done drugs, snorted 6 lines of cocaine. The girl is concerned because her boyfriend is complaining of palpitations and is extremely agitated.
Upon arrival to the house you find a 17 year old male pacing around the house wearing dark sunglasses. As you question the young man, he informs you that he has never had any health problems in the past and that his friends pressured him into trying the cocaine. The young man tells you that he feels like his heart is going to jump out of his chest and that he feels like he cannot sit still.
On examination, the young man has dilated, blood-shot eyes, and he is tachycardic (with a heart rate of 135). He is also hypertensive (with a blood pressure of 200/120). He has clear respirations. The rest of his physical exam is normal, except for his inability to remain still.
-The Patient History:
1) This patient reports no significant past medical history, so a chronic medical disease most likely does not apply here.
2) This patient admits to cocaine use, which can stimulate the sympathetic nervous system (see the “cocaine toxicity” section below for more details).

3) The patient states that he is having palpitations and is agitated, which is consistent with cocaine use.
-The Physical Exam:
1) The patient is tachycardic, with a heart rate of 130, secondary to sympathetic (Betaadrenergic) stimulation.
2) The patient is hypertensive, with a blood pressure of 200/120, secondary to sympathetic (alpha-adrenergic) stimulation.
3) The patient is wearing sunglasses because sympathetic stimulation has caused his eyes to dilate.
4) The patient is extremely agitated, which often results from an overwhelming sympathetic response in some patients.
-Description:
Cocaine is a naturally occurring extract of the coca bush, Erythroxylon coca , a plant which is indigenous to South America.
-Pharmacology:
Cocaine is absorbed across all mucosal surfaces, including: the oral, nasal, gastrointestinal, and vaginal epithelium. Consequently, cocaine can be applied topically, swallowed, injected intravenously, or smoked in the form of crack or free base cocaine. When cocaine is used nasally, the peak effect occurs within 15 to 25 minutes, and its duration of action lasts around 1 to 3 hours. The intravenous and inhalational methods have rapid onsets and have durations of effect lasting around 15 to 30 minutes.
4
-Effects:
Cocaine is both a local anesthetic and a central nervous system stimulant.
-Local Anesthetic: Like other local anesthetics, cocaine inhibits conduction of nerve impulses by blocking fast sodium channels in the cell membrane.
-Cardiovascular Effects: Cocaine has very dynamic effects on the heart. For example, in large doses, cocaine can be toxic to the myocardium of the heart, resulting in wide complex dysrhythmias and tachycardia. In addition, cocaine can activate the sympathetic nervous

system through the excess release of neurotransmitters, which can lead to hypertension and tachycardia.
-Other Effects: Sympathetic activation can also lead to other characteristic physical exam findings, such as mydriasis (or eye dilation) and diaphoresis (or sweating). In addition, excess sympathetic stimulation predisposes a person to dysrhythmias, seizures, hyperthermia, and agitation.
-See figures that follow.

A concerned wife calls the emergency medical services complaining that her husband is bleeding uncontrollably. The woman tells the dispatcher that the man was using a chain saw to cut down a tree when he lost control of the saw and sliced his thigh open. She states that he cut himself an hour ago and that she was hesitant to call an ambulance because her husband kept stating that he was, “fine and not goin’ to any darn hospital.” The woman says that she became concerned because the man had bled through 6 to 7 bath towels and was getting more pale and weak by the minute.
On arrival to the house, you find a very pale 35 year old man surrounded by bloodsoaked towels, barely holding his head up. You quickly ask the wife some questions. You specifically inquire if the patient has any history of heart disease or bleeding disorders. In addition, you ask about the time of her husband’s last food or drink intake and about any medications that he may be taking. She states he has generally been healthy and that he does not take any regular medications.
Upon examination, the patient is tachycardic, with a pulse of 145, and hypotensive, with a blood pressure of 75/30. You notice that, as soon as direct pressure is removed, the wound spurts bright red blood nearly to the ceiling.

-The Patient History:
1) This patient is a healthy man who has sustained a laceration to his thigh.
2) The patient’s wife states that it has been over an hour since the patient was lacerated, and the bleeding is still not controlled. This places the patient at risk for serious hemorrhage.
3) The patient’s pallor and the presence of several blood soaked towels suggest a significant loss of blood.
-The Physical Exam:
1) The patient is pale, indicating poor tissue perfusion secondary to hemorrhage.
2) The patient’s laceration appears very deep, and the blood coming from the wound is projectile, indicating an arterial bleed. Recall that the arterial system is under much more pressure than the venous system. Consequently, wounds in which the bleeding is pulsatile or projectile, suggest that the bleed is most likely originating from an artery. Venous bleeding can also be very significant but the flow from the wound is generally slow and steady.
3) The patient’s vital signs (tachycardia and hypotension) suggest that he has lost a significant amount of blood and may be in hemorrhagic shock.
-Causes:
Injuries to major vascular structures, solid organs, and large bones are the most common causes of severe traumatic hemorrhage. Common non-traumatic causes of hemorrhage include: gastrointestinal bleeding, vascular aneurysm rupture, and ruptured ectopic pregnancy.
-Pathophysiology:
The acute loss of vascular volume triggers a wide range of physiological regulatory responses aimed at compensating for the blood loss and maintaining perfusion to the most important vascular beds in the body. The compensatory physiologic responses to acute hemorrhage attempt to maintain adequate tissue oxygen delivery and sustain cellular function.
The loss of circulating blood volume stimulates the sympathetic nervous system, which results in increased heart rate, arterial and venous vasoconstriction, increased cardiac contractility, and vascular fluid shifts. Despite the body’s compensatory mechanisms, if severe

hemorrhage is not controlled, the body’s lack of perfusion eventually affects the heart and brain, and will result in death.
The normal blood volume in an adult is around 5 to 7 liters. Usually, loss of blood in the range of 1 liter to 1.5 liters will result in tachycardia. As blood loss exceeds 1.5 liters, the patient will exhibit further tachycardia and hypotension. With blood losses greater than 2 liters, the body’s compensatory responses to the blood loss will begin to become overwhelmed, unless adequate resuscitation is initiated.
2,3,5
-See figures that follow.

The cardiovascular system is one of the most complex and durable organ systems in the human body. Due to the considerable complexity of this organ system, it is easy to get bogged down with the intricate details of cardiovascular anatomy and physiology. This can make it difficult to rapidly and accurately identify what may be wrong with your patients. However, understanding that the cardiovascular system, in its most basic form, consists of a pump (the heart) that transports blood (the vehicle) through a series of highways (the vessels) can help you conceptualize problems that may arise.
The purpose of this course was to add to your knowledge of cardiovascular anatomy and physiology, so that you can quickly identify, assess, and determine the appropriate management and disposition of a patient suffering from cardiovascular-related emergencies. In addition, this course attempted to provide you with information that will assist you in being able to convey more information to the emergency department staff and, ultimately, provide an even higher quality of care to your patients.