Page 37 - Small Animal Internal Medicine, 6th Edition

CHAPTER 1 Clinical Manifestations of Cardiac Disease 9

ventricle accelerates aortic closure. Pathologic splitting of S 2 arises from sudden checking of ventricular filling by the
can result from delayed ventricular activation or prolonged constrictive pericardium; its timing is similar to the S 3 .
VetBooks.ir RV ejection secondary to ventricular premature beats, right Cardiac Murmurs
bundle branch block, a ventricular or atrial septal defect, or
There are many causes for cardiac murmurs. Most involve a
pulmonary hypertension.
structural cardiac abnormality and are considered patho-
Gallop Sounds logic murmurs. However, some murmurs do not and are
The third (S 3 ) and fourth (S 4 ) heart sounds occur during considered nonpathologic. Nonpathologic murmurs are sys-
diastole (see Fig. 1.9) and are not normally audible in dogs tolic in timing. They can occur for physiologic reasons, for
and cats. When an S 3 or S 4 sound is heard, the heart can example, when blood viscosity is reduced by anemia, or
sound like a galloping horse, hence the term gallop rhythm. when cardiac output is increased from fever, hyperthyroid-
This term can be confusing because the presence or absence ism, etc.; these are known as functional murmurs. Sometimes
of an audible S 3 or S 4 has nothing to do with the heart’s a soft murmur is heard in an animal without evidence for
rhythm (that is, the origin of cardiac electrical activation and structural cardiac disease or physiologic alteration. These are
the intracardiac conduction process). Gallop sounds usually considered innocent murmurs and often are found in young
are heard best with the bell of the stethoscope (or by light puppies. Many animals with a pathologic murmur also have
pressure applied to a single-sided chestpiece) because they other clinical signs consistent with heart disease. However,
are of lower frequency than S 1 and S 2 . At very fast heart rates, pathologic as well as nonpathologic murmurs often are dis-
differentiation of S 3 from S 4 may be impossible. If both covered as incidental findings on physical examination. In
sounds are present, they may be superimposed, which is these cases, it is important to determine if a clinically impor-
called a summation gallop. tant cardiac disease or physiologic abnormality is the cause
The S 3 gallop, also known as an S 3 gallop or ventricular or not. Careful physical examination and auscultation can
gallop, is associated with low-frequency vibrations at the end help the clinician decide how aggressively (or whether) to
of the rapid ventricular filling phase. An audible S 3 in the dog immediately pursue additional diagnostic testing.
or cat usually indicates ventricular dilation with myocardial Cardiac murmurs are described by their timing within
failure. The extra sound often is very subtle although some- the cardiac cycle (systolic or diastolic, or portions thereof),
times it can be fairly loud and easily detected; it is heard best intensity, PMI on the precordium, radiation over the chest
over the cardiac apex. This sound may be the only auscult- wall, quality, and pitch. Systolic murmurs can occur in early
able abnormality in an animal with dilated cardiomyopathy. (protosystolic), middle (mesosystolic), or late (telesystolic)
An S 3 gallop also may be audible in dogs with advanced systole or throughout systole (holosystolic). Diastolic
mitral valve disease and CHF. murmurs generally occur in early diastole (protodiastolic) or
The S 4 gallop, also called an atrial or presystolic gallop, throughout diastole (holodiastolic). Murmurs at the end of
is associated with low-frequency vibrations triggered by diastole are termed presystolic. Continuous murmurs begin
blood flow into the ventricles during atrial contraction (just in systole and extend through S 2 into all or part of diastole.
after the P wave of the ECG). An audible S 4 in the dog Murmur intensity generally is graded on a scale of 1 to 6
or cat usually is associated with increased ventricular stiff- (sometimes written I to VI) (Table 1.1). The PMI usually is
ness and hypertrophy, such as with hypertrophic cardio- indicated by the hemithorax (right or left) and valve area or
myopathy or hyperthyroidism in cats. A transient S 4 gallop intercostal space where it is located, or by the terms apex or
of unclear significance sometimes is heard in stressed or base. Because murmurs can radiate extensively, the entire
anemic cats. thorax, thoracic inlet, and carotid artery areas should be
auscultated. The pitch and quality of a murmur relate to its
Other Transient Sounds frequency and subjective assessment. “Noisy” or “harsh”
Other brief abnormal sounds are audible in some cases. Sys- murmurs contain mixed frequencies. “Musical” murmurs
tolic clicks are mid-to-late systolic sounds that usually are are of essentially one frequency with its overtones; these can
heard best over the mitral valve area. These sounds have been sound like a “whoop” or “honk.”
associated with degenerative valvular disease (endocardio- Murmurs also can be described by their phonocardio-
sis), mitral valve prolapse, and congenital mitral dysplasia; a graphic configuration (Fig. 1.10). A plateau-shaped or
concurrent mitral insufficiency murmur can be present. In “regurgitant” murmur begins at the time of S 1 and remains
dogs with degenerative valvular disease, a mitral click might of fairly uniform intensity throughout systole. Sometimes
be the first abnormal sound noted, with a murmur develop- this murmur configuration also is called holosystolic, because
ing over time. An early systolic, high-pitched ejection sound it generally is consistent throughout systole. Loud regurgitant/
at the left base can occur in animals with valvular pulmonic holosystolic murmurs can mask the S 1 and S 2 sounds. AV
stenosis or other diseases that cause dilation of a great artery. valve insufficiency and interventricular septal defects com-
The sound is thought to arise from either the sudden check- monly cause this type of murmur because turbulent blood
ing of a fused pulmonic valve or the rapid filling of a dilated flow begins at the time of AV valve closing and continues
vessel during ejection. Rarely, constrictive pericardial disease throughout ventricular systole. A crescendo-decrescendo or
causes an audible pericardial knock. This diastolic sound diamond-shaped murmur starts softly, builds intensity in