Etiology Pathology and Physiology of the Prolapsed Valve Syndrome

1. What is the usual mitral valve abnormality seen at surgery or necropsy when a prolapsed mitral valve is examined?

ANS: Myxomatous transformation with elongated chordae. (See figure on p. 226.)

On the left is a cross section of the abnormal middle scallop of the posterior leaflet. On the right is the same area from a woman with left ventricular hypertrophy but no MR. (From J. K. Trent, et al. Am. Heart J. 79:539, 1970.)

2. With what conditions have prolapsed valves been most commonly associated?

ANS: a. The Marfan syndrome.

b. Papillary muscle dysfunction due to myocardial infarction.

c. Hypertrophic obstructive cardiomyopathy (HOCM).

d. Atrial septal defects (ASDs).

3. What is the cause of the nonejection click preceding the delayed systolic murmur?

ANS: The "chordal snap" theory contends that the click is due to a sudden stretch of chordae as they give way with the peak pressure in midsystole. However, because the papillary muscles contract early, the chordae are under too much tension from the beginning of systole to "snap" during ventricular ejection. Therefore, this theory has been challenged by another theory that suggests that the click is a valvular sound produced by the loss of support of one leaflet by its opposing leaflet due to redundant valve tissue or to an abnormality of chordal length [5]. Thus, a small piece of unsupported leaflet may suddenly flip upward to its full extent to produce a click.

Note: a. Other causes of midsystolic clicks include a small left-sided pneumothorax, pleuro-pericardial adhesions, absent pericardium, and an aneurysm of the atrial septum or of the membranous ventricular septum, usually with a small VSD. b. An early diastolic click may be heard in 5-15% of patients with MVP, due to reverse ballooning of the prolapsed mitral leaflets.

4. How much MR is present if a delayed murmur to the S2 is present?

ANS: Since there is little or no regurgitation at the beginning of systole in these patients, only a mild to moderate amount of MR is likely to be present with this kind of murmur.

5. What can cause the development of heart failure in a patient with mild MR secondary to the prolapsed valve syndrome, besides ruptured chordae?

ANS: Infective endocarditis on the mitral valve can occur.

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