Ventricular septal defects
In patients with ventricular septal defects, you will hear a loud (grade 4 to 6) right basilar systolic murmur. The ventricular
septal defect presents an instance in which the grade of the murmur is inversely related to the effect on the heart. The loud
murmur implies normal ventricular chamber pressures and functions and has a better prognosis. As the heart starts to fail,
the murmur actually grows softer. The ventricular septal defect and tricuspid regurgitation are the common right-sided murmurs
you will hear (Table 3).
Table 3: Most common heart murmurs based on type and location
Relative pulmonic stenosis
You may hear a fairly loud (grade 3 to 4) left basilar systolic murmur in the presence of a ventricular septal defect. This
murmur, known as relative pulmonic stenosis, sounds much like pulmonic stenosis. This is the sound of an increased volume of blood passing through a normal-sized orifice.
The blood shunting through the defect to the right ventricle is added to the normal volume of blood returning from the right
atrium. Together these represent an increased volume trying to pass through the pulmonic valve. Since the amount of time the
heart has to move this extra volume remains unchanged, it must increase the blood velocity thereby creating turbulence and
a murmur. In the case of an atrial septal defect, the shunt itself does not make a murmur, and if the volume of the shunt
is not sufficient to create relative pulmonic stenosis, you will hear no murmur.
During your auscultation, be sure to note the cardiac rhythm. Pauses, skips, bursts, rapid changes in rate, or asynchrony
are indicative of arrhythmias. Rhythms, such as atrial fibrillation, are so completely asynchronous they are distinctive,
and you can practically diagnose them by auscultation alone. This arrhythmia is often described as having the sound of tennis
shoes in the dryer because of the chaotic rhythm. Premature complexes sound like skips in the rhythm and may be ventricular
or atrial in origin. During this phase of the examination, you should palpate an arterial pulse in the patient to detect any
pulse deficits created by any arrhythmia. A pulse deficit is detected when a heart sound is heard but no corresponding pulse
is felt. The femoral pulse is most easily accessible in dogs and cats. A facial artery can be used in horses or cattle.
With some practice, you can become proficient at cardiac auscultation. Just remember, only by actually listening carefully
to every patient, especially normal ones, can you improve your skills.
H. Edward Durham Jr., CVT, LATG, VTS (Cardiology), is a technician at the College of Veterinary Medicine Veterinary Medical
Teaching Hospital at the University of Missouri in Columbia, Mo. He is also a charter member of the Academy of Internal Medicine
for Veterinary Technicians and serves on its executive board as the Director at Large-Cardiology.