KEY POINTS
• In order to make sense of the sounds heard during cardiac auscultation, a thorough understanding of which valves should be open and which should be closed during systole (cardiac contraction) and diastole (cardiac relaxation) is needed.
• Blood, like all fluids, flows from an area of high pressure to an area of low pressure. Pressure gradients determine the direction and velocity of blood flow as well as when the valves open and close.
• Fluid is a fairly efficient carrier of sound. If pathology generates turbulent blood flow within the heart, the associated murmur usually radiates to a fairly predictable location.
• Auscultation is carried out at five to six discrete areas on the precordium. Each of these areas is associated with a particular valve; however, not all pathology associated with a valve can be heard best at its named anatomic location.
Cardiac auscultation can be frustrating to learn. Many physical examination textbooks present cardiac auscultation in a simplistic fashion: Simply memorize a table, auscultate the precordium in five spots with the stethoscope bell and diaphragm, and arrive at a diagnosis. Clinicians who seek to further refine their skills are confronted with a variety of audio programs that present a dizzying array of cardiac recordings. The average clinician quickly discovers that it will take years of practice to become skilled in cardiac auscultation.
Given the easy availability of echocardiography and other technologic interventions in many locations, auscultation may not appear to be a cost-effective skill to learn. Some authors believe that a marked deterioration in cardiac physical examination skills is occurring.1 Repeated studies have demonstrated what is being referred to as a "disturbingly low identification rate" for common murmurs.2-4
As complex and subtle as many cardiac auscultatory findings are, a return to the fundamental principles learned in basic science classes will assist the clinician with arriving at a diagnosis in many cases. Instead of encouraging memorization, this article discusses how knowledge of the anatomy and physiology of the heart assists with making an accurate diagnosis.
CARDIAC ANATOMY AND PHYSIOLOGY
Effective evaluation of a heart murmur is very difficult to accomplish without a thorough understanding of the cardiac cycle and its associated circulatory pattern. In order to make sense of the sounds heard during cardiac auscultation, a thorough understanding of which valves should be open and which should be closed during systole (cardiac contraction) and diastole (cardiac relaxation) is needed. The heart has four major valves that promote a unidirectional flow of blood through the circulatory system. The valves are located in a band of fibrocartilaginous tissue in the center of the heart5 (Figure 1). A healthy valve is quite pliable; it opens with little resistance and closes, or coapts, tightly to prevent retrograde blood flow.
The atrioventricular (AV) valves—mitral valve and tricuspid valve —separate the atria from the ventricles. The mitral valve is located between the left atrium and left ventricle; the tricuspid valve is located between the right atrium and right ventricle. These valves prevent retrograde blood flow into the atria during ventricular systole. Although simple in appearance, AV-valve function is complex. AV valves rely on anchoring apparatus (the chordae tendineae and papillary muscles) and on proper ventricular wall motion during systole to coapt tightly. Anything that hampers heart wall motion, such as ischemia, can contribute to valve dysfunction.
The semilunar valves—aortic valve and pulmonic valve —
separate the ventricles from the major vessels that leave the heart—the aorta and the pulmonary artery. The architecture of the semilunar valves is somewhat simpler than that of the AV valves. The semilunar valves have three leaflets with deep cusps. The depth of the cusps forms a large surface area for coaptation. The semilunar valves prevent retrograde blood flow into the ventricles during diastole.
Systole Intraventricular pressure rapidly increases as systole begins. The AV valves close, normally synchronously, producing the heart sound called S1. The mitral component of S1 is usually louder than the tricuspid component because pressures in the left side of the heart are greater. As the pressure in the ventricles becomes greater than the pressure in the great vessels, the aortic valve and pulmonic valve open, allowing forward blood flow. This flow is usually silent.