Gallop rhythm may be defined as the addition of an audible diastolic sound to the two normal heart tones. Such a triple rhythm may occur as an atrial gallop producing a low-pitched sound after atrial systole, but before the subsequent ventricular contraction. An atrial gallop sound is a frequent auscultatory finding, particularly in hypertensive cardiovascular disease and in the presence of a prolonged atrioventricular conduction time.
In view of evidence relating this sound to a ventricular pressure wave resulting from atrial contraction, it was thought that further information about the genesis of the atrial gallop might be obtained by altering intracardiac pressure relationships. This was accomplished by means of tourniquet pooling of blood in the extremities of 18 hospitalized patients, 17 with severe hypertensive cardiovascular disease, and 1 with pulmonary hypertension. Observations made by simultaneous phonocardiograms and apex cardiograms indicated that after 5 minutes of venous pooling there was a striking diminution in the intensity of the atrial gallop sound and that it moved closer to the first heart sound in two-thirds of the cases. It is thus apparent that by artificially lowering central venous pressure, atrial systole results in somewhat less blood being ejected into the ventricle, which in turn is under less tension. Under these conditions, the production of the atrial gallop sound in hypertensive cardiovascular disease is altered, so that it occurs later and often becomes inaudible.