Patent Ductus Arteriosus

Amara Estrada, DVM, DACVIM (Cardiology) University of Florida

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A continuous murmur is auscultated high on the left heart base in this recording; it increases and decreases in intensity throughout the cardiac cycle with the peak intensity near the S2 sound.

Unlike a to-and-fro murmur, this continuous murmur never stops, but increases and decreases throughout the cardiac cycle. The most common cause of a continuous murmur is patent ductus arteriosus (PDA) with its classic “machinery-like” murmur noted throughout the cardiac cycle. It should be noted that the murmur could cease in late diastole with slow heart rates; the diastolic component can eventually disappear with the development of pulmonary hypertension. Other rare causes of continuous murmurs include aortopulmonary window, ruptured aneurysms of sinus of Valsalva, and coronary arteriovenous fistulae.

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