The most likely diagnosis in our patient is mitral valve prolapse, as characterized by apical mid systolic clicks and a mid-to-late systolic crescendo murmur both of which are altered by maneuvers.
MVP causes
Mitral valve prolapse is a very common cause of mitral regurgitation and must be distinguished from other causes, including papillary muscle dysfunction, mitral annular calcification, endocarditis, and rheumatic heart disease.
In addition, other causes of systolic murmurs that may be heard at the apex include ventricular septal defect, the mitral regurgitation murmur of hypertrophic obstructive cardiomyopathy and aortic stenosis.
Prevalence & Dx
Mitral valve prolapse is common. The prevalence ranges from one to five percent. Patients with mitral valve prolapse usually are asymptomatic. However, as in our patient, they may complain of palpitations or chest pain that is not typical of angina. No established pathophysiologic relationship of these symptoms to the prolapse itself exists. The diagnosis is generally reliable when it is based on auscultation. A bedside maneuver such as standing or squatting can help to verify the auscultatory diagnosis. Characteristic auscultatory findings may vary from exam to exam in the same patient.
Auscultatory findings spectrum
The spectrum of the auscultatory findings in patients with mitral valve prolapse includes the following: isolated mid-to-late systolic click or clicks; an isolated mid-to-late systolic murmur; mid-to-late systolic click(s) introducing a mid-to-late systolic murmur; a holosystolic murmur; an unusual systolic "whoop" or "honk" when the late systolic murmur takes on a musical characteristic.
Pathophysiology
The pathophysiology characteristic of the auscultatory findings in patients with mitral valve prolapse involves a mismatch between the elongated chordae tendineae and the deformed leaflets of the mitral valve relative to the size of the left ventricular cavity.
In mitral valve prolapse the chordae-leaflet tandem is too large for the size of the ventricle. The systolic murmur is not present in early systole because the left ventricle is maximally distended and the mismatch is minimal. As systole progresses, the left ventricular cavity becomes smaller, allowing the elongated chordae to extend and the deformed mitral leaflets to billow into the left atrium. This leads to loss of coaptation of the leaflets, allowing mitral regurgitation and producing the mid-to-late systolic crescendo murmur. Maneuvers that change left ventricular cavity size, alter the characteristics of the auscultatory findings. They are useful for establishing the clinical diagnosis of mitral valve prolapse.
Postural effects
This diagram shows the effects of postural maneuvers on the mid systolic click and subsequent murmur in patients with mitral valve prolapse. Standing accentuates the cavity-valve mismatch by decreasing left ventricular volume and cavity size. This causes the click and murmur of mitral regurgitation to occur earlier, that is, closer to the first heart sound. Occasionally, a click or murmur will be heard only during such an intervention. The Valsalva strain phase causes similar findings. In contrast, squatting increases left ventricular volume by enhancing venous return and increasing afterload, thus, lessening the cavity-valve mismatch. This decreases the severity of mitral regurgitation and causes the click and murmur to occur later, that is, closer to the second sound. Elevation of the legs with the patient supine to increase venous return, causes a similar effect.
Valsalva
During the strain phase of the Valsalva maneuver, venous return to the left atrium is markedly reduced, resulting in a decrease in left ventricular cavity size. This causes the click and murmur of mitral regurgitation to begin earlier. Absence of either the click or murmur with a combination of standing and Valsalva strain phase virtually excludes the diagnosis of mitral valve prolapse. [Sounds]
Illustration
This illustration shows simultaneous left heart intracardiac pressures, a phonocardiogram and the left ventricular volume curve. On auscultation, the first part of systole is silent. The mid systolic click introduces the murmur. Both occur as the ventricle becomes progressively smaller. [Sounds]