Homeostatic imbalances
• Pericarditis inflammation of the
pericardium
• Endocarditis bacterial infection of the
endocardium can lead to valvular stenosis
• Myocardial infarction heart
attack/coronary
• Heart block any damage to the AV node
results in irregular beating of ventricles
• Murmurs abnormal or unusual hearts
sounds
ECG: normal and abnormal
Alterations in
Electrocardiogram
Clinical Cardiology Concepts for Vets
20-3
Cardiac Output
• Cardiac Output - the amount of blood
pumped by a ventricle per minute. Units may
be in milliliters or Liters per minute.
• Heart Rate - number of cardiac cycles per
minute. Average for males = 64-72/min.
Average for females = 72-80/min.
• Stroke Volume - amount of blood pumped out
of a ventricle each beat. Average resting
stroke volume = 70 ml.
Cardiac Output
• CO (mL/min) =SV (70 mL/beat) X HR (75
beat/min)
– Cardiac output = stroke volume X heart rate = 5250ml/min
• SV= EDV - ESV
– Stroke volume = end diastolic volume – end systolic volume
• Cardiac reserve is the difference between a
person’s maximum cardiac output and cardiac
output at rest.
Frank Starling Law of the Heart
• The more cardiac muscle is stretched within
physiological limits, the more forcibly it will
contract.
• Rubber band analogy
• Increasing volumes of blood in ventricles
increase the stretch & thus the force
generated by ventricular wall contraction.
• Greater stretch means more blood volume is
pumped out, up to physical limits.
Regulation of stroke volume
• Preload is the degree of stretch on the
heart.
• Contractility is the force of ventricular
contractions.
• Afterload is the pressure that must be
exceeded to eject blood from the ventricles.
• The Frank-Starling law of the heart—preload
is the critical factor controlling SV (stroke
volume).
Regulation of heart rate
• When blood volume drops or the heart is
weakened, SV drops and the HR increases.
– Positive chronotropic factors increase HR.
– Negative chronotropic factors decrease HR.
• Extrinsic regulation by the ANS
– Sympathetic nervous system increases firing of
the pacemaker and enhances Ca2+ entry into
heart cells.
– Parasympathetic nervous system reduces heart
rate through ACh which opens K+ channels.
– Under resting conditions the PNS is dominant
Chemical Regulation
• Hormones
– Epinephrine enhances HR and contractility
– Thyroxine enhances effects of Epi and NE and
leads to slower more sustained increase in HR
• Ions
– Hypocalcemia (Ca2+)depresses the heart;
– Hypercalcemia prolongs the plateau phase and
lead to heart irritability
– Hyperkalemia (K+) may lead to heart block and
cardiac arrest; hypokalemia leads to arrhythmia
and weakened contractions.
– Excess Na+ blocks Ca2+ inflow, decreasing
contractile strength
Other Factors
• Exercise leads to a reduced HR when at rest.
• Working large body muscles for at least 20
minutes elevates cardiac output and
accelerates metabolism.
– Athletes have a larger heart and a resting HR of
40-60 beats per minute
• Increased temperature increases heart rate;
decreased temperatures reduce heart rate
and oxygen needs.
Homeostatic imbalances
• Congestive heart failure
– Caused by Coronary artherosclerosis
– Caused by  Persistent high blood pressure
– Caused by Multiple myocardial infarcts
– Left side failure Pulmonary congestion
– Rights side failure Peripheral congestion
Angina Pectoris
• Medical term for chest pain due to coronary
heart disease.
• It occurs when the myocardium doesn’t get
as much blood (Oxygen) as it needs.
• Insufficient blood supply is called ischemia.
• May initially occur during physical exercise,
stress, or extreme temperatures.
• It is a sign of increased risk of heart attack.
Cardiac Arrhythmias
• Arrhythmias irregular heart rhythms that may
lead to fibrillation
• Tachycardia: Heart rate in excess of 100bpm
• Bradycardia: Heart rate less than 60 bpm
• Sinus arrhythmia: Heart rate varies 5% during
respiratory cycle and up to 30% during deep
respiration
• Premature atrial contractions: Occasional
shortened intervals between one contraction
and succeeding, frequently occurs in healthy
people
Aneurysm
• Weakness of the wall of an artery causing an
abnormal enlargment or bulge.
• The aorta or the arteries that supply the
heart, brain, legs or kindeys are most
commonly affected.
Atherosclerosis (Arteriosclerosis)
• Narrowing and hardening of arteries and
impairment of blood flow due to the
deposition of fatty materials and calcium in
their walls.
• Risk factors include:
– smoking
– inactivity
– diabetes
– high blood cholesterol
– personal or family history of heart disease
– Atherosclerosis Animation
Resources
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Heart Sounds & Cardiac Arrhythmias
Live Cardiac Exam Video
Anatomy Links
Cardiac Cycle
Cardiac Cycle Graphics
Interactive Physiology Review
AP II Notes Homepage
Conducting System of Heart