Definitions and Causes

1. What are the two definitions of a continuous murmur?

ANS: a. The murmur never stops, i.e. it is truly continuous throughout systole and diastole.

b. The murmur can be heard to go beyond the S2 but stops before the next Sj, i.e., it is not truly continuous but does envelop the second sound and goes more than slightly beyond it.

2. What is a systolic and diastolic murmur heard in the same area called if it is not continuous?

ANS: A to-and-fro murmur. This implies that the systolic component is due to blood flowing in one direction and the diastolic murmur is due to flow in the opposite direction, e.g., an AS ejection murmur plus an AR murmur. A continuous murmur, on the other hand, implies a murmur that is due to continuous flow in the same direction in both systole and diastole.



3. Are all continuous murmurs regurgitant?

ANS: No. Continuous murmurs may be caused by a. Partial obstruction to a vessel, as in bilateral peripheral pulmonary artery stenosis.

Excessively rapid flow through tortuous vessels, as in collateral circulation secondary to a coarctation of the aorta. Extracardiac arterial or venous turbulence:

(1) The mammary souffle (see below).

(2) Bronchial collateral circulation in cyanotic congenital heart disease with severe obstruction to pulmonary arterial flow.

(3) An arteriovenous fistula.

(4) Total anomalous pulmonary venous connection (heard under either clavicle).

(5) Across a small ASD with mitral stenosis (Lutembacher syndrome) or with MR (best in right third or fourth intercostal spaces).

Phonocardiogram from a patient with a PDA. The S2 at the apex marks the beginning of diastole for the tracings of the continuous murmur, which envelops and obliterates the second sound at the left sternal border. This murmur did not sound truly continuous at the third left interspace (3 LIS), since it seemed to end in mid-diastole. The pulmonary artery systolic pressure was 35 mmHg. The pulmonary flow was slightly more than twice the systemic flow.

4. Why should you search for a continuous murmur in the arms, legs, or abdomen in any patient in congestive failure of obscure etiology?

ANS: A search must be made for an arteriovenous fistula, congenital or traumatic. If such a fistula is large (1 cm or more in diameter), signs and symptoms of failure may occur over a period of years.

5. What is the most common cause of a continuous murmur?

ANS: Persistent ductus arteriosus, usually called patent ductus arteriosus or PDA. (All ducti are patent, otherwise it would be a ligamentum arteriosum.)

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