Cardiac Auscultation
Basic Information 
Overview and Goal(s)
• Cardiac auscultation is the systematic examination of the heart using a stethoscope.
• Auscultation is both expedient and relatively sensitive for detection of serious heart disease when performed by a knowledgeable and experienced examiner.
• This examination is most useful for measurement of heart rate, recognition of persistent arrhythmias, and detection of congenital heart malformations and acquired valvular diseases.
• Pericardial diseases also may be recognized by auscultation.
• This procedure is conducted in the context of a medical history and general physical examination, which includes assessment of the precordium and pulses, auscultation of the thorax, and inspection for edema and abnormal ventilatory patterns.
Indications
Auscultation is indicated as part of every clinical examination. It is particularly important in horses with signs of potential heart disease, including exercise intolerance, reduced performance, falling, tachypnea, abnormal jugular pulses, ventral edema, and weight loss. Auscultation also is important before sedation or anesthesia.
Equipment, Anesthesia
• A good-quality stethoscope is required, but the specific instrument used is a matter of personal preference.
• The diaphragm should be applied firmly and used for most of the examination.
• The bell should be applied lightly, creating an air seal against the skin, and is most useful for detecting low-frequency sounds (third sound) and soft diastolic murmurs.
• Combination chest pieces use a “tunable diaphragm” in which mild pressure accentuates lower pitched sounds (bell function) and progressively firmer pressure optimizes higher frequency sounds.
Anticipated Time
Precordial palpation and cardiac auscultation should take approximately 2 minutes on the left thorax and 1 minute or less on the right. Palpation or inspection of the pulses should add no more than an additional 1 to 2 minutes.
Preparation: Imporant Checkpoints
• The horse should be restrained by an assistant whenever possible.
• The examination should be conducted in a quiet area.
• The examiner must be knowledgeable of the procedure, with an understanding of both normal and abnormal heart sounds.
Normal equine heart sounds include the fourth, first, second, and third sounds, designated by their historical discovery. The general cadence of these sounds is “ba-lub … dup-ah” (4-1…2-3).
The fourth, or atrial, sound is presystolic and follows the P wave of the electrocardiogram and vibrations of the atrial contraction. It is isolated following a blocked P wave of atrioventricular block and is absent in atrial fibrillation. When closely timed to the following first sound, a “pseudo-split” sound is detected. The P-R interval determines the proximity of the atrial to the first heart sound.
The long and lower pitched first sound follows the QRS complex and indicates the onset of ventricular systole. The higher frequency second sound heralds the onset of ventricular diastole. These sounds can be closely split in healthy animals.
The third sound occurs near the termination of rapid ventricular filling and is the softest, lowest pitched, and most variable of the normal sounds.• The heart sounds should be correlated to the cardiac impulse and the arterial and venous pulses.
The left apical (cardiac) impulse occurs near the fifth intercostal space and represents the area just ventral to the mitral valve. The first sound, and often the third, are loudest at this point. The external impulse develops during early systole and forms a useful timing clue for the cardiac cycle.
The arterial pulse can be identified in the facial artery, carotid artery, and forelimbs. This event is timed approximately to mid-systole. Arrhythmias can cause rapid, slow, irregular, or variable pulses. Significant aortic regurgitation or the rare aortocardiac fistula can create a hyperkinetic or bounding pulse. Heart failure, pericardial effusion, and volume depletion cause hypokinetic pulses and often resting sinus tachycardia in the 60 to 70 beats/min range. Marked respiratory variation in pulse pressure can be observed with pericardial effusion (pulsus paradoxicus).
Pulsations and diameter of the jugular veins are reflective of right atrial pressures that vary from positive to subatmospheric during the cardiac cycle. When the head is elevated, the jugular vein should not be distended and pulsations should be limited to the lower third of the neck. The finding of jugular venous distension suggests right heart failure, cardiac tamponade, or a cranial mediastinal mass. Jugular pulsations are usually physiologic and relate to atrial contraction. Pathologic retrograde venous pulses can be caused by congestive heart failure, tricuspid regurgitation, and some heart rhythm disturbances.Possible Complications and Common Errors to be Avoided
Cardiac auscultation is noninvasive and unlikely to lead to complications. However, a number of examination or interpretation pitfalls can be identified.
• Subtle abnormalities may be missed in a noisy environment, if the approach is not systematic, or if the examiner is not sufficiently attentive to the task at hand.
• Failure to listen over the right thorax may lead to a missed murmur of tricuspid regurgitation or a ventricular septal defect.
• Inability to time systole and diastole can foster erroneous conclusions. The left apical impulse and arterial pulse are both systolic events. However, even with these clues, some heart murmurs can be confusing, such as with the late systolic, crescendo murmur of mitral valve prolapse and the variable presystolic murmur related to atrial contraction.
• The functional ejection murmur and the murmur of mitral regurgitation (MR) are the primary murmurs to distinguish on the left side; distinction is made based on timing and point of maximal intensity (see below).
• The functional protodiastolic (filling) murmur and the murmur of aortic regurgitation (AR) are usually distinguished by age (older horses acquire AR) and timing (AR is generally holodiastolic). However, early or very mild AR can also be protodiastolic in timing.
• Prominent jugular pulsations can be misinterpreted in otherwise normal horses in relation to head position (too low), misinterpretation of normal collapse and refill as a pathologic pulse, and not appreciating that the carotid artery pulse can be transmitted across the jugular vein.
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