Arrhythmogenic Mitral Valve Prolapse (AMVP)

Mitral valve prolapse is common and in most people is not associated with arrhythmia. The arrhythmic phenotype appears to arise from a combination of valve morphology and the mechanical consequences of prolapse on the adjacent myocardium.^[2]

Mitral annular disjunction is a separation between the left atrial wall at the level of the mitral annulus and the basal left ventricular myocardium. It permits exaggerated systolic motion of the annulus and is associated with the arrhythmic phenotype.^[3]

Repeated traction on the papillary muscles and inferobasal wall is the proposed mechanism for the fibrosis found in these regions at autopsy and on imaging, providing an arrhythmic substrate.^[2]

Arrhythmogenic mitral valve prolapse is not a single-gene disorder and there is no established genetic test for it. Familial clustering of mitral valve prolapse is recognised, and the 2022 consensus statement addresses family assessment where there has been a sudden death or where prolapse is familial.^[1]

Genetic testing has a defined role where the presentation raises an alternative or coexisting inherited diagnosis, for example an arrhythmogenic cardiomyopathy, rather than as a routine test for prolapse itself.^[1]

Mitral valve prolapse is common in the general population. What is uncommon is the arrhythmic phenotype, and the consensus statement notes that the true prevalence of arrhythmic mitral valve prolapse is not well established because case definitions have varied between studies.^[1]

Series of young sudden death that include mitral valve prolapse suggest it accounts for a small but consistent minority of cases, with bileaflet involvement over-represented compared with prolapse in the general population.^[2]

The diagnosis rests on documenting prolapse together with ventricular arrhythmia that is not explained by another cause.^[1]

Features that raise concern in a person with prolapse:

• Bileaflet prolapse^[2]
• Mitral annular disjunction^[3]
• T-wave inversion in the inferolateral leads^[2]
• Frequent, complex, or polymorphic ventricular ectopy, particularly with a right bundle branch block morphology arising from the papillary muscles^[1]
• Late gadolinium enhancement of the papillary muscles or inferobasal wall^[1][2]
• Unexplained syncope, or a family history of premature sudden death^[1]

The presence of prolapse alone, without arrhythmia, does not establish the diagnosis, and the great majority of people with mitral valve prolapse do not have the arrhythmic phenotype.^[1]

• Echocardiography: characterise the prolapse, quantify regurgitation, and look specifically for mitral annular disjunction, which is easily overlooked if not sought^[3]
• 12-lead ECG: inferolateral T-wave inversion^[2]
• Ambulatory ECG monitoring: to quantify ectopy burden and capture complex or polymorphic forms^[1]
• Cardiac MRI: the key test for tissue characterisation, looking for papillary muscle and inferobasal late gadolinium enhancement^[1][2]
• Exercise testing: for exercise-induced arrhythmia^[1]

Where a person presents after an aborted cardiac arrest, the assessment is that of unexplained cardiac arrest, and prolapse should not be assumed to be the cause until alternatives have been excluded.^[4]

1. General measures: confirm the arrhythmia burden and exclude alternative causes before attributing arrhythmia to the valve. Address electrolytes, thyroid status and stimulants.

2. Medical therapy: beta-blockers are commonly used first line for symptomatic ventricular ectopy. Antiarrhythmic drug choice otherwise follows general principles for ventricular arrhythmia.^[1]

3. Catheter ablation: can be considered for ventricular ectopy or ventricular tachycardia arising from the papillary muscles, recognising that these sites are technically demanding and recurrence is not unusual.^[1]

4. Device therapy: ICD for secondary prevention as above; primary prevention individualised.^[1][4]

5. Mitral valve surgery: indications follow those for mitral regurgitation. Surgery should not be undertaken on the expectation that it will abolish the arrhythmia, since the evidence that valve repair removes arrhythmic risk is limited.^[1]

• Sustained ventricular arrhythmia and cardiac arrest, the concern that defines the entity^[2]
• Progressive mitral regurgitation, with its own consequences for ventricular function and atrial arrhythmia
• Heart failure where regurgitation is severe or long-standing

Risk stratification here is not yet on a firm evidence base, and the consensus statement says so directly.^[1] The features listed under Diagnosis are those associated with arrhythmic events in observational series, not validated components of a risk score.

In a cohort study of mitral annular disjunction, disjunction was associated with ventricular arrhythmia independently of the presence or severity of mitral regurgitation, which is part of why the arrhythmic risk is not simply a function of valve leak.^[3]

Secondary prevention follows established indications: an ICD is indicated after resuscitated cardiac arrest or sustained ventricular tachycardia, as for other causes.^[4]

Primary prevention is where uncertainty sits. Decisions are individualised, weighing the arrhythmic phenotype, imaging substrate and family history, and are best made in a service that sees this regularly.^[1]

Follow-up is individualised. Reasonable components are periodic review of symptoms, echocardiography to track regurgitation severity and ventricular dimensions, and repeat ambulatory monitoring where the arrhythmia burden influenced management.^[1]

Where mitral annular disjunction and an arrhythmic phenotype are present, follow-up should sit with a service able to reassess risk as the evidence base develops.^[1]

• Do not extrapolate from the minority to the majority. Mitral valve prolapse is common and usually benign; the arrhythmic phenotype is the exception.^[1]
• Look for annular disjunction deliberately. It is not reported unless it is sought, and it carries arrhythmic association independent of regurgitation severity.^[3]
• Do not rely on regurgitation severity as the risk marker. Arrhythmic risk in this group is not simply a function of how leaky the valve is.^[3]
• Be honest about the evidence. Primary prevention ICD decisions here rest on limited data, and the consensus statement is explicit about that uncertainty.^[1]
• Do not offer surgery as arrhythmia treatment. Operate for the usual mitral regurgitation indications, and counsel that arrhythmia may persist afterwards.^[1]