Student Handout
Heart Sounds
Introduction
In this laboratory you will record and analyze an ECG, phonocardiogram (PCG), and
pulse from a volunteer and examine the temporal relationships among them. Then you
will ‘meet’ a patient with a cardiovascular problem, analyze his test results, see findings
from specialized investigations into his problem and study his ECGs and PCGs. You will
also examine the ECGs and PCGs from three other patients with cardiovascular
problems.
Background
Why understanding heart disease is important in nursing
Heart disease is relatively prevalent in the community and ranks highly among causes of
admission to hospitals. It is also a very common cause of death. The heart of a person
who lives for 80 years will beat about 3000 million times!
Every time the heart contracts and relaxes it goes through one complete cardiac cycle
(Figure 2). During each cycle heart valves open and close. Closure generates sounds
that can be heard using a stethoscope. A variety of cardiac abnormalities can give rise to
additional sounds - heart murmurs. You will see patients with a variety of abnormal heart
sounds and murmurs.
A little history
Raymond Vieussens (ca 1635 –1715), a French anatomist and physician, was the first to
describe mitral stenosis and aortic insufficiency. He wrote “I have mentioned that to
begin with the circulation of the blood was embarrassed by the excessive narrowing of
the opening into the left ventricle”. His book published in 1715, "Traité nouveau de la
structure et des causes du mouvement naturel du coeur" [A new treatise on the structure
and causes of the natural movement of the heart], provided one of the earliest
discussions of the correlation between the clinical symptoms of heart disease and the
underlying pathophysiology.
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Heart Sounds
Raymond Vieussens (ca 1635 –1715)
The first illustration of mitral stenosis. From
Raymond Vieussens book published 1715.
What the heart does
The heart is a dual pump that circulates blood around the body and through the lungs.
Blood enters the atrial chambers of the heart at a low pressure and leaves the ventricles
at a higher pressure. The high arterial pressure provides the energy to force blood
through the circulatory system. Figure 1 shows a schematic of the organization of the
human heart and the circulatory system. Blood returning from the body arrives at the
right side of the heart and is pumped through the lungs. Oxygen is picked up and carbon
dioxide is released. This oxygenated blood then arrives at the left side of the heart, from
where it is pumped back to the body.
Heart valves and heart sounds
Each side of the heart is provided with two valves, which convert the rhythmic
contractions into a unidirectional pumping. The valves close automatically whenever
there is a pressure difference across the valve that would cause backflow of blood.
Closure gives rise to audible vibrations (heart sounds). Atrioventricular (AV) valves
between the atrium and ventricle on each side of the heart prevent backflow from
ventricle to atrium. Semilunar valves are located between the ventricle and the artery on
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Heart Sounds
each side of the heart, and prevent backflow of blood from the aorta and pulmonary
artery into the respective ventricle.
Figure 1. A schematic diagram of the human heart and circulatory system.
The closure of these valves is responsible for the characteristic sound produced by the
heart is usually referred to as a 'lub-dub' sound. The lower-pitched 'lub' sound occurs
during the early phase of ventricular contraction. This is produced by closing of the
atrioventricular (mitral and tricuspid) valves. These valves prevent blood from flowing
back into the atria. When the ventricles relax, the blood pressure drops below that in the
artery, and the semilunar valves (aortic and pulmonary) close, producing the higherpitched 'dub' sound. Malfunctions of these valves often produce an audible murmur,
which can be detected with a stethoscope.
The cardiac cycle
The sequence of events in the heart during one cardiac cycle is summarized in Figure 2.
During ventricular diastole blood is returning to the heart. Deoxygenated blood from the
periphery enters the right atrium and flows into the right ventricle through its open AV
valve. Oxygenated blood from the lungs enters the left atrium and flows into the left
ventricle through its open AV valve. Filling of the ventricles is completed when the atria
contract (atrial systole). In the resting state, atrial systole accounts for some 20% of
ventricle filling. Atrial contraction is followed by contraction of the ventricles (ventricular
systole). Initially, as the ventricles begin to contract the pressure in them rises and
exceeds that in the atria. This closes the AV valves. But, until the pressure in the left
ventricle exceeds that in the aorta (and in the right ventricle exceeds that in the
pulmonary artery), the volume of the ventricles can not change. This is the so-called
isovolumic phase of ventricular contraction. Finally, when the pressure in the left
ventricle exceeds that in the aorta (and the pressure in the right ventricle exceeds that in
the pulmonary artery), the aortic and pulmonary valves open and blood is ejected into
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Student Handout
Heart Sounds
the aorta and pulmonary arteries. As the ventricular muscle relaxes, pressures in the
ventricles fall below those in the aorta and pulmonary artery, and the aortic and
pulmonary valves close. Ventricular pressure continues to fall and once it has fallen
below that in the atria, the AV valves open and ventricular filling begins again.
Figure 2. A schematic diagram of cardiac cycle.
The electrical activity of the heart
Cardiac contractions are not dependent upon a nerve supply. However, innervation by
the parasympathetic (vagus) and sympathetic nerves does modify the basic cardiac
rhythm. Thus the central nervous system can affect this rhythm. The best known
example of this is so-called sinus arrhythmia where respiratory activity affects the heart
rate.
A group of specialized muscle cells, the sinoatrial, or sinuatrial (SA) node acts as the
pacemaker for the heart (Figure 3). These cells rhythmically produce action potentials
that spread through the muscle fibers of the atria. The resulting contraction pushes blood
into the ventricles. The only electrical connection between the atria and the ventricles is
via the atrioventricular (AV) node. The action potential spreads slowly through the AV
node, thus allowing atrial contraction to contribute to ventricular filling, and then rapidly
through the AV bundle and Purkinje fibers to excite both ventricles.
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Heart Sounds
Figure 3. Components of the human heart involved in conduction.
The cardiac cycle involves a sequential contraction of the atria and the ventricles. The
combined electrical activity of the different myocardial cells produces electrical currents
that spread through the body fluids. These currents are large enough to be detected by
recording electrodes placed on the skin (Figure 4). A recording of this electrical activity is
an electrocardiogram (ECG).
Figure 4. Standard method for connecting the electrodes to a volunteer.
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Heart Sounds
The regular pattern of peaks during one cardiac cycle is shown in Figure 5.
Figure 5. One cardiac cycle showing the P wave, QRS complex and T wave.
The action potentials recorded from atrial and ventricular fibers are different from those
recorded from nerves and skeletal muscle. The cardiac action potential is composed of
three phases: a rapid depolarization, a plateau depolarization (which is very obvious in
ventricular fibers) and a repolarization back to resting membrane potential (Figure 5).
Figure 6. A typical ventricular muscle action potential.
The components of the ECG can be correlated with the electrical activity of the atrial and
ventricular muscle:
• The P-wave is produced by atrial depolarization.
• The QRS complex is produced by ventricular depolarization; atrial repolarization
also occurs during this time, but its contribution is insignificant.
• The T-wave is produced by ventricular repolarization.
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Heart Sounds
Wiggers Diagrams
Changes in a variety of parameters during one cardiac cycle are usefully summarized in
a figure introduced by Wiggers. A modified form of this is shown in Figure 7. The
importance of this representation is that it allows you to see the temporal relationships
between the different parameters.
Figure 7. A Wiggers' diagram.
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Heart Sounds
Valvular Heart Disease
In this Laboratory, you will examine recordings from patients with 4 common valvular
heart lesions - mitral stenosis and incompetence (regurgitation, insufficiency) and aortic
stenosis and incompetence (regurgitation, insufficiency).
By listening to the heart, it is possible to decide which of these conditions is present. In
this laboratory, you will see the heart sounds recorded at the same time as the patient's
ECG. This enables you to determine the timings of the heart sounds and murmurs
accurately in relation to the cardiac cycle.
Mitral Valve
Mitral Stenosis
In mitral stenosis, there is a narrowing of the orifice of the mitral valve. Blood flows from
left atrium to left ventricle through this valve during ventricular diastole. With mitral
stenosis, a low pitched, mid-diastolic murmur is heard. There is often a louder than
normal first sound as the mitral valve is shut more forcibly than normal.
Mitral Insufficiency
In mitral Insufficiency, damage to the valve structure leads to a leak of blood back from
the contracting ventricle to the left atrium. This leak results in a high-pitched murmur
heard throughout systole. Because of the greater blood volume in the left atrium, there is
a very rapid filling of the left ventricle when the mitral valve opens in early diastole. This
gives rise to a 3rd heart sound.
Aortic Valve
Aortic Stenosis
In aortic stenosis, a narrowed aortic valve impedes blood flow into the aorta during
ventricular systole. This results in a characteristic systolic murmur that increases in
loudness to mid-systole and then fades gradually. The second heart sound may be
softer than normal, too.
Aortic Insufficiency
In aortic insufficiency, the defective valve does not close properly so that, during early
diastole, blood flows back into the ventricle. This results in an early diastolic murmur that
follows the second heart sound and gradually decreases in intensity.
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Treating patients with heart conditions
Treating heart conditions often requires multiple medications. These can include;
•
Angiotensin-converting enzyme (ACE) inhibitors. These agents are used to
treat hypertension and heart failure. By inhibiting ACE, arteriolar resistance is
decreased. ACE inhibitors can be identified by the suffix '-pril' and common ACE
inhibitors are captopril, benazepril, lisinopril, cilazapril and enalapril. Potential
side effects with these drugs include cough, headache, drowsiness, hypotension,
rash and renal failure.
•
Antiarrhythmic agents. This large class of drugs includes agents that suppress
cardiac arrhythmias through a variety of mechanisms, including β-adrenoceptor
antagonism and calcium, sodium and potassium channel blocking. Examples of
antiarrhythmic agents are quinidine, lidocaine, propranolol, amiodarone,
verapamil and digoxin. Drug interactions can occur between amiodarone and
warfarin, and also between amiodarone, quinidine and propafenone and digoxin.
Amiodarone can also cause skin appear blue-grey in color.
•
Anticoagulants. These agents are used to reduce the risk of blood clots leading
to heart attacks or strokes, and can also be prescribed if a patient has undergone
heart valve replacement. Warfarin is a common anticoagulant, but its use must
be monitored carefully due to numerous interactions with other drugs, including
aspirin and certain diuretics, antibiotics, fibrates, and antiarrhythmia medications,
cranberry products and grapefruit juice. Patients on anticoagulant medication
should also avoid excessive consumption of green, leafy vegetables, as this will
reduce the drug's effects.
•
Antiplatelet agents. Antiplatelet drugs are considered better at preventing
arterial clots than anticoagulants. They work by reducing platelet aggregation and
inhibiting thrombus formation. Examples of antiplatelet drugs are acetylsalicylic
acid (aspirin), clopidogrel, dipyridamole and ticlopidine. Because antiplatelet
medications can cause gastrointestinal upset (nausea, stomach pain, diarrhea), it
is recommended that these agents been taken with food. Also, antiplatelets
increase the risk of bleeding, which should be considered in patients who may
require surgery.
•
β-adrenoceptor antagonists (also known as beta blockers). These are drugs
that inhibit the action of epinephrine and norepinephrine to reduce cardiac output
and blood pressure. Unwanted side effects of β-adrenoceptor antagonists are dry
mouth and skin, bronchoconstriction, bradycardia and hypoglycaemia. Some βadrenoceptor antagonists may interact with diabetes and asthma medicines.
•
Calcium channel blockers. This class of drugs slows down the electrical
conductivity of the heart, leading to a lower heart rate and reduced blood
pressure. Some examples of calcium channel blockers are verapamil, diltiazem,
amlodipine and nifedipine.
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•
Cholesterol-lowering medications. These agents include statins, resins,
nicotinic acid, fibrates and cholesterol absorption inhibitors. These drugs reduce
cholesterol synthesis, increase bile synthesis (which uses cholesterol), reduce
triglyceride levels, or block cholesterol absorption from food. The end result is
less cholesterol in the bloodstream. Gastrointestinal upsets (nausea, diarrhea,
vomiting, constipation), headaches and arrhythmia are common side effects with
this class of drugs. Drug interactions have been noted for warfarin, erythromycin
and cholesterol-lowering medications.
•
Diuretics. Diuretics are often used in patients with high blood pressure. By
promoting the kidneys to remove excess salt and fluid from the blood, blood
pressure is lowered. They are also useful in treating edema. Possible side effects
of diuretics include weakness, muscle cramps, rash, gastrointestinal upset,
dizziness, and increased sensitivity to sunlight. Furthermore, diuretics should not
be used in combination with digoxin or digitalis, cyclosporine or other
medications for high blood pressure.
•
Nitrates. Nitrates act as vasodilators and are used to treat chest pain. Nitrates
may be administered orally in the form of a pill, lozenge or translingual spray, in a
topical ointment, or skin patch. Common side effects with these agents are
dizziness, headaches, gastrointestinal upset, low blood pressure and arrhythmia.
Drug interactions have been noted with erectile dysfunction medications, cold
and flu medications and with high blood pressure treatments.
Other important aspects of caring for patients with heart conditions include dietary,
smoking and exercise interventions.
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Heart Sounds
What you will do in the class
In this class you will perform three exercises and examine one case study.
1. Heart sounds. You will begin by using a stethoscope to listen to the heart.
2. ECG and PCG in a resting volunteer. You will record the ECG and PCG of a
volunteer at rest, then analyze the signals.
3. ECG, PCG, and pulse. You will record and analyze the ECG, PCG, and pulse of
a volunteer.
Patient Case Study: You will ‘meet’ Mr H, a patient with a heart murmur, and use the
results of investigations into his problem to develop a Nursing diagnosis and patient care
plan. Three supplementary patient cases are also provided for further study.
References
Bray J., Cragg P. A., Macknight A., Mills R., Taylor D. Lecture Notes: Human Physiology
5th Edition, edited by Petersen O.H. (Blackwell Publishing, 2007)
Rang H.P., Dale M.M., Ritter J. M. Pharmacology 6th Edition (Elsevier Science, 2007)
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