MVP Revisited
August 1, 1999 5 minutes read
MVP Revisited
abstracts & commentarySynopsis: The prevalence of MVP is lower than previously reported and the incidence of adverse sequelae is low. MVP defined by new, more specific, echocardiographic criteria is not more common among young individuals with cerebral ischemic events.
Sources: Freed LA, et al. N Engl J Med 1999;341:1-7; Gilon D, et al. N Engl J Med 1999;341:8-13.
Mitral valve prolapse (mvp) is believed to be a common disorder that may cause symptoms and lead to valve replacement. However, the true prevalence of MVP in the community setting has not been established since two-dimensional echocardiographic criteria were refined. Thus, Freed and colleagues evaluated the two-dimensional echocardiograms in 3736 unselected subjects participating in the Framingham Offspring Study. Technically inadequate echoes excluded 245 (7%). MVP was analyzed in the parasternal and apical long axis views, and superior displacement of the leaflets greater than 2 mm and at least a 5-mm-thick leaflet were required to diagnose classic MVP. Nonclassic MVP was diagnosed when leaflet thickness was less than 5 mm. MVP was found in 84 subjects (2%): 47 with classic and 37 with nonclassic (1% each). Complications in the MVP patients included syncope in three, atrial fibrillation in one, stroke in one, one had endocarditis, and one had mitral valve replacement. These incidences of the complications were similar to those without MVP.
Most patients with classic MVP had mild mitral regurgitation, whereas those with non-classic and those without had trace regurgitation. Severe regurgitation occurred in 7% vs. 0 vs. 0.5%, respectively. Sixty percent of the MVP subjects were women and MVP subjects were leaner than the others (BMI 24 vs 27; P < 0.001). Systolic murmurs and clicks were more prevalent in MVP subjects vs. the others (P < 0.001) and were found in about one-quarter of the classic MVP subjects. Symptoms of chest pain and dyspnea were not more frequent in MVP subjects. Freed et al conclude that in a community-based population sample using modern echo criteria, the prevalence of MVP is lower than previously reported and the incidence of adverse sequelae is low.
A higher prevalence of MVP has been reported in young patients with cerebrovascular events, but the true prevalence with modern two-dimensional echocardiographic criteria is unknown. Thus, Gilon and associates used a case-controlled design to evaluate 213 patients 45 years old or younger with ischemic stroke or transient ischemic attacks (TIA) by echocardiography and compared them to 263 controls. Cardiac or vascular causes of the cerebral ischemic event were identified in 142 of the 213 patients; 93 had major vessel disease in the neck and 49 had a cardiac source of embolism. Of the 71 without overt cardiovascular disease, only 16 had no risk factors for cerebral ischemic events. MVP was found in four of the 213 cerebral event cases (2%) and seven of the 263 controls (3%). Interestingly, none of the patients in either group had classic MVP, more than trace MR, or left atrial enlargement. The frequency in the 71 patients without identifiable cardiovascular disease was 3% and none of the 16 without any risk factors for cerebral ischemic events had MVP. Gilon et al conclude that MVP defined by new, more specific, echocardiographic criteria is not more common among young individuals with cerebral ischemic events as compared to controls.
Comment by Michael H. Crawford, MD
These two studies are important because they are the first attempt to re-evaluate MVP in light of the new echocardiographic diagnostic criteria by the investigators who developed the new criteria. Not surprisingly, the prevalence of MVP is much less than previously believed, is similar in men and women, and is evenly distributed over adult ages in Freed et al’s study.
Whether 2% is the true incidence in the U.S. population is less certain since the study population is relatively small and homogeneous. Also, this is a cross-sectional study in which only the survivors are evaluated. However, it is free of the sick population selection bias of hospital-based studies. Certainly, the 5-35% incidence of previous reports is erroneous and the true value is probably less than 5%. This is extremely important because a low disease prevalence in a population renders screening tests such as echocardiography useless from a cost-effectiveness point of view. What about patients with symptoms? Wouldn’t they have a higher prevalence and make echocardiography more valuable as a screening tool? Freed et al’s study indirectly answers this question by documenting that symptoms are no more frequent in the MVP patients than in the others. Also, Gilon et al’s study demonstrates that even young patients with cerebral ischemic events do not have a higher incidence of MVP and most of them have other traditional risk factors for stroke. Thus, without other evidence of cardiac disease, nonspecific cardiac symptoms and cerebral ischemic events are not an indication for echocardiography to look for MVP.
Before we close the echo lab, it is still true that MVP is the most common cause of mitral valve surgery in the United States and some patients with MVP do have complications. MVP is a spectrum from normal variants to severe myxomatous changes such as seen in certain hereditary disease such as Marfan’s syndrome. Freed et al’s study uses an operational classification based upon an arbitrary cutoff of leaflet thickness of more than 5 mm representing "classic MVP." Using this cutoff point confined severe regurgitation almost exclusively to the classic group. Other studies have shown that complications such as heart failure, endocarditis, and the need for surgery are much more common in the classic group. Freed et al showed that mitral regurgitation was usually trivial in the nonclassic MVP and normal subjects but was mild or greater in the classic cases. This suggests that antibiotic prophylaxis may be necessary only in the classic cases or those with more than mild mitral regurgitation, but this remains to be proven.
Not surprisingly, the physical examination was not very effective at detecting MVP since it is well known that most cases of mild mitral regurgitation are not detectable by auscultation. However, since the prognosis of patients with mild or less mitral regurgitation is unknown, but presumably largely benign even if they have MVP, echocardiography to detect such patients does not seem cost-effective. In Freed et al’s study, complications attributed to MVP were very low (6%) and not significantly different from the non-MVP subjects (7%). This study showed that mitral valve clicks and systolic murmurs were more frequent in classic MVP (11% and 22%, respectively) than in nonclassic MVP (8% and 10%) or normals (1.5% and 4%), which was statistically significant (P < 0.001). Also, this study confirmed that MVP patients tend to be thinner than normals (BMI 24 vs 27; P < 0.001).
Even though MVP is generally benign, the clinician cannot ignore the person with MVP. Most of the subjects with MVP in Freed et al’s study would not have gotten an echo outside this protocol because less than one-third would have specific cardiac symptoms or physical findings. The data suggest that the nondetection of these patients is acceptable since their complication rate is very low and the detection methods are expensive and will have a low yield if applied broadly. An echo is certainly justifiable in those with specific cardiac symptoms and signs, but not those with cerebrovascular disease and no evidence of cardiac disease. Also, specific cardiac symptoms and signs are more frequent in the classic cases of MVP where complications are more likely. (Dr. Crawford is Robert S. Flinn Professor, Chief of Cardiology, University of New Mexico, Albuquerque.)
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