continuous murmur

Continuous murmurs occur due to blood flow across a structure that maintains a pressure gradient between two connected structures (e.g., aorta and pulmonary artery, or artery and vein) during both systole and diastole, without a silent gap at S2. This differentiates it from combined systolic and diastolic murmurs, which do have a brief pause at S2.

Key causes: - Patent ductus arteriosus (PDA): most common cause; 'machine-like' continuous murmur, loudest at S2, heard best at left infraclavicular/upper sternal border; associated with congenital rubella syndrome, prematurity; wide pulse pressure and bounding pulses. - Venous hum: common benign finding in children, heard in the neck/supraclavicular area, disappears with the patient lying down or with jugular venous compression. - Coronary AV fistula. - Ruptured sinus of Valsalva aneurysm. - Aortopulmonary window. - Mammary souffle: benign, occurs during late pregnancy/lactation due to increased blood flow through breast vasculature. - Arteriovenous fistula (surgical, e.g., for dialysis, or traumatic).

Pathophysiology: The murmur results from turbulent, continuous flow due to a persistent gradient across a communication (e.g., a PDA connects the higher-pressure aorta to the lower-pressure pulmonary artery in both systole and diastole).

Clinical significance: Recognizing continuous murmurs helps localize congenital or acquired vascular/cardiac shunt lesions. In neonates, a continuous murmur strongly suggests PDA, especially in the context of prematurity or maternal rubella infection during pregnancy. Treatment of PDA involves indomethacin or surgical/catheter closure, though can be kept open with prostaglandins if congenital heart defects require it for survival (e.g., transposition of great vessels).

Distinguishing features for boards: Continuous murmur (no gap at S2) vs. to-and-fro murmur (a combination of systolic and diastolic components with a brief silent period at S2, as seen in aortic regurgitation plus stenosis).