Cardiac auscultation is an important and basic component of a physical examination in clinical practice. For the experienced listener, auscultation provides quick and reliable diagnostic information about the state of the heart. Phonocardiography systems allow the listener to record these findings. Spectral phonocardiographic studies, introduced as early as 1955 by McKusick et al,1 accurately characterize the quality of heart sounds and cardiac murmurs by creating a graphic record. Recording heart sounds and phonocardiograms enables building heart sound libraries and teaching material.2-4 Dr. Proctor Harvey's audio tapes are classics in adult cardiology.
The significant improvements in personal computers over the past few decades have made it possible to design new highly capable phono-spectrocardiographic devices with digital signal analysis. Published studies have demonstrated the clinical validity of this method of recording and analyzing cardiac sounds.5-9 Digital signal processing allows the combination of phonocardiography with other imaging modalities.
Heart sounds provide information about both normal and pathologic physical events in the heart. The movement of blood and the movement and vibration of the heart structures produce audible sounds and murmurs. The causes of vibratory movement in the cardiovascular system can be categorized into two general mechanisms: (1) rapid acceleration and deceleration of blood flow or (2) continuous turbulence in blood flow. The sudden sounds caused by acceleration and deceleration of blood flow are called heart sounds, and the sounds produced by turbulent blood flow are labeled murmurs.
Phonocardiography is a diagnostic technique that graphically records cardiac acoustic phenomena.10 Visualization of heart sounds may help in understanding cardiac events (Fig. 2–1). A visual record may also help an inexperienced listener recognize and classify auscultatory findings. The essential elements of the phonocardiographic system are a transducer (microphone), an amplifier, a filter, and recording, analyzing, and transcription systems. In the past, all of the parts, including those needed for recording and transcription, were analog.
Heart sound events represented graphically. The red bars represent left-side events, and the black bars represent right-side events. The gray area is normally inaudible. The first heart sound (S1) contains two components: the mitral valve closure sound (M1) and the tricuspid valve closure sound (T1). The second heart sound (S2) contains two components: the aortic valve closure sound (A2) followed by the pulmonary valve closure sound (P2). The presystolic (atrial) gallop sound (S4) is normally inaudible. The prodiastolic (ventricular) gallop (S3) may be audible and is normal in children. Innocent systolic murmur (SM) is a common normal finding, especially in children. Ejection sounds (E) are normally inaudible. Opening snaps (O), if audible, indicate some level of pathology. Adapted from Leatham.10