Listening to the heart provides a window into its mechanical function. This technique, known as auscultation, uses a stethoscope to detect the sounds produced by the heart as it beats. These sounds offer clues about the heart’s health and structure. Analyzing the rhythm, pitch, and timing helps identify sounds that deviate from a normal pattern, which can signify conditions requiring further investigation.
The Foundation of Normal Heart Sounds
Every heartbeat produces two primary sounds, S1 and S2, commonly described as “lub” and “dub.” These represent the sound of heart valves snapping shut. The S1 sound is generated by the closure of the mitral and tricuspid valves as the ventricles begin to contract. This marks the beginning of systole, the phase when the heart pumps blood to the body.
Following S1 is the S2 sound, occurring as the aortic and pulmonic valves close. This signals the start of diastole, the period when the ventricles relax and refill with blood. S2 is higher-pitched than S1, and the consistent S1-S2 sequence constitutes a normal heartbeat, serving as the baseline against which all other sounds are compared.
Understanding Heart Murmurs
Heart murmurs are sounds generated by turbulent blood flow across a heart valve. This turbulence can result from a valve that doesn’t open fully (stenosis) or one that doesn’t close properly (regurgitation). In stenosis, blood is forced through a constricted opening, while with regurgitation, blood leaks backward through the valve.
Murmurs are classified by their timing. A systolic murmur occurs between the S1 and S2 heart sounds, while a diastolic murmur is heard after S2. The character of a murmur provides further clues; for instance, aortic stenosis produces a harsh, rising-and-falling systolic murmur, while aortic regurgitation can cause a soft, blowing diastolic murmur.
The loudness of a murmur is graded on a scale from 1 (very faint) to 6 (audible without a stethoscope) to quantify its intensity.
Exploring Gallops, Clicks, and Rubs
Other distinct sounds can indicate specific cardiac events. Gallop rhythms consist of extra heart sounds, S3 and S4, that create a cadence resembling a galloping horse. The S3 sound, or ventricular gallop, is a low-pitched sound occurring early in diastole. While it can be normal in young people and athletes, in older adults it often suggests a condition like congestive heart failure.
The S4 sound, or atrial gallop, is a low-pitched sound heard just before S1. It is produced when the atria contract forcefully to push blood into a stiff ventricle. An S4 is often associated with conditions like long-standing hypertension. Unlike S3, an S4 sound is almost always a sign of an underlying cardiac issue.
Other sounds include clicks and rubs. A mid-systolic click is a short, high-pitched sound and a classic sign of mitral valve prolapse, where the mitral valve leaflets bulge back into the left atrium. A pericardial friction rub is a high-pitched, scratching sound caused by inflammation of the pericardium, the sac surrounding the heart. This sound can be heard during both systole and diastole.
Anatomical Listening Posts for Auscultation
To accurately assess heart sounds, specific listening locations on the chest are used that correspond to different heart valves. These sites are not directly over the valves but are locations where the sound from each valve is best heard as it radiates. The four primary auscultation areas are the aortic, pulmonic, tricuspid, and mitral areas.
The aortic area is at the second intercostal space to the right of the sternum, where sounds from the aortic valve are most prominent. The pulmonic area is at the second intercostal space to the left of the sternum, where sounds from the pulmonic valve are best detected.
The tricuspid area is found at the fourth or fifth intercostal space along the lower left sternal border, which is the optimal site for hearing the tricuspid valve. The mitral area is located at the apex of the heart, in the fifth intercostal space at the mid-clavicular line. This is the prime location for identifying sounds from the mitral valve, including the click associated with mitral valve prolapse.