High-frequency sounds of brief duration are occasionally present in patients with transvenous pacemakers located in the RV apex. They are extracardiac in origin, occurring nearly synchronously (within 6-10 ms) with the pacemaker spike, and are due to stimulation of intercostal nerves adjacent to endocardial electrodes.270 This stimulus results in contraction of the intercostal muscles, and frequently twitching of the muscle can be observed. The presence of these sounds always should suggest possible myocardial perforation by the endocardial lead, although this is not always present. Stimulation of the pectoral muscles, as well as diaphragmatic stimulation, also has been reported to produce these extracardiac sounds. They also have been observed in patients having transthoracically placed epicardial leads.
Inflammation of the pericardial sac with or without fluid may cause a pericardial friction rub. These friction sounds are very high-pitched, leathery, and scratchy in nature. They seem close to the ear and are auscultated best with the patient leaning forward or in the knee-chest position, holding his or her breath after forced expiration. The pericardial rub may have three components during the intervals of the cardiac cycle when the heart has the greatest excursions within the pericardial sac-at the time of atrial systole, at the time of ventricular contraction, and during rapid early diastolic filling. The usual friction rub occurs during the first two intervals, although three-component rubs may be heard. Triple-component friction rubs are common in uremic pericarditis, particularly when the underlying cardiac disease is hypertension. In this situation, the heart is hyperkinetic due to both pressure and volume overload as well as to the anemia associated with renal failure. Pericardial friction rubs are very common in the acute phase of transmural MI, although they often last for only a few hours. There is a common misconception that friction rubs are not heard when there is a large amount of fluid in the pericardial sac; this is not the case, because usually some portions of the visceral and parietal pericardial surfaces are in contact despite the large amount of fluid (see Chap. 72).
Occasionally, certain midsystolic (ejection) murmurs have a scratchy character and may be misinterpreted as friction rubs. This is particularly true of the short, scratchy pulmonic ejection murmur heard in hyperthyroidism (Means-Lerman sign).274 Such scratchy sounds should not be considered to be a friction rub unless both systolic and diastolic components are heard.
Mediastinal Crunch: Hamman's Sign
When air is present in the mediastinum, a series of scratchy sounds (Hamman's sign272) may occur, related indirectly to both heartbeat and respiratory excursion. These sounds occur most frequently during ventricular systole and in a random fashion. The diagnosis of mediastinal emphysema may be confirmed by crepitation in the neck secondary to subcutaneous air. These crunching sounds due to air in the mediastinum are common following cardiac surgery.
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