[HKU Medical Grand Rounds] The rare facet of a common disease – mitral valve prolapse

Case history and management

A 47-year-old gentleman with a known history of mitral valve prolapse (MVP) and mild-to-moderate mitral regurgitation since his 30s presented to Queen Mary Hospital with sudden onset of chest pain and palpitations for 1 day.

During clinical assessment, his heart rate was 200 beats per minute (bpm), with a blood pressure of 98/62 mm Hg. The patient was fully alert and not in respiratory distress. There were no signs of overt heart failure and no stigmata of infective endocarditis. Physical examination revealed grade 3 pansystolic murmur at the apex with radiation to the axilla compatible with known history of MVP and mitral regurgitation.

Electrocardiography (ECG) showed regular wide complex tachycardia of 200 bpm with a right-bundle-branch-block–like pattern and north-west axis deviation, suggestive of ventricular tachycardia (VT). (Figure 1)

VT was terminated with intravenous amiodarone, which revealed underlying atrial flutter with a ventricular rate of 50 bpm. Laboratory test showed elevated high-sensitivity troponin T (833 ng/L) and creatine kinase (400 U/L). Echocardiography showed a mildly dilated left ventricle with normal ejection fraction of 60 percent. There was moderate left atrial enlargement and prolapse at A2/A3 segments of the mitral valve with severe posterolaterally directed mitral regurgitation. (Figures 2 and 3)

Urgent coronary angiography excluded significant coronary artery disease. Cardiac MRI showed a mildly impaired left ventricular (LV) ejection fraction of 52 percent with scarring in the posterior papillary muscle and the inferior wall of the left ventricle. (Figure 4) Electrophysiology voltage mapping revealed scarring and double potentials extending from the tip to the base of the posterior papillary muscle to 2 cm towards the LV septum. VT was confirmed to be arising from the base of posterior papillary muscle.

Subsequently, the patient underwent surgical mitral valve repair and cryoablation of atrial flutter and VT. Subcutaneous implantable cardioverter defibrillator (S-ICD) was implanted for secondary prevention of sudden cardiac death (SCD) before discharge from hospital. At subsequent clinic follow-up, no shock episodes recorded from the ICD were found. Reassessment echocardiography showed normal left ventricle dimensions and no significant residual mitral regurgitation.

This case illustrates a rare presentation of MVP complicated with VT and severe mitral regurgitation successfully treated with surgical arrhythmia ablation and valvular repair.

Discussion

Overview of diagnosis of mitral valve prolapse

The prevalence of MVP in the general population is around 2–3 percent.¹ It is an imaging diagnosis and defined as systolic billowing of any portion of the mitral leaflets ≥2 mm above the annular plane into the left atrium in the long axis view. (Figure 5) It can be classified into primary and secondary MVP based on aetiology.

Primary MVP refers to prolapse of the mitral valve resulting from myxomatous degeneration. It can be further classified into classic and nonclassic subtypes based on morphology. The classic subtype, also known as Barlow’s disease, has marked and diffuse thickening of leaflets (≥5 mm) with bileaflet prolapse. In the nonclassic subtype, the mitral valves usually have limited or absent thickening and segmental prolapse.

Fibroelastic deficiency is a less common entity and may be seen in elderly patients. In such cases, valvular involvement is more focal, leaflets are not thickened or redundant, and chordae are thin and friable. The same valve may exhibit fibroelastic deficiency as well as focal myxomatous change in different areas.

Secondary MVP refers to prolapse of the mitral valve due to mechanisms other than myxomatous degeneration (eg, connective tissue disease, rheumatic heart disease, papillary muscle rupture due to ischaemia, trauma, cardiomyopathy, etc).

Presentation of mitral valve prolapse

Most patients with MVP are asymptomatic and commonly present with incidental finding of a heart murmur leading to evaluation by echocardiography. Patients can also present with nonspecific symptoms such as chest pain and palpitations. In complicated cases, heart failure symptoms ensue as mitral regurgitation progresses. Fever and embolic complications due to infective endocarditis are uncommon presentations of the disease. In rare occasions, patients may present with malignant arrhythmia (eg, VT and ventricular fibrillation or even SCD especially in those with moderate-to-severe mitral regurgitation).

Ventricular arrhythmia and sudden death in mitral valve prolapse

The risk of ventricular arrhythmia and SCD in patients with mitral valve disease is not well defined. The risk of sudden death is estimated to be 0.2 percent/year to 0.4 percent/year in prospective studies.²

Evidence on the causative role of MVP in SCD is mostly from registry data. In a cardiac pathology registry from Italy that included 650 young adults aged <40 years with SCD, 43 patients (7 percent) were found to have MVP.³ Similar to our case, MRI evidence of myocardial scarring was found in a majority (93 percent) of patients with known MVP and complex ventricular arrhythmia. Among those patients, the site of scarring was also in the papillary muscles and inferior LV wall.

Due to the relative paucity of data, currently there is no specific risk-stratification guideline for SCD in patients with MVP. However, patients with a history of cardiac arrest or ventricular arrhythmias are generally considered to be at high risk for SCD. Flail mitral leaflet, significant mitral regurgitation and impaired LV systolic function are other risk factors proposed.⁴ Focal gadolinium enhancement in papillary muscle was also commonly observed in those with ventricular arrhythmias, but its clinical and prognostic significance is still undetermined.³

Prevention of ventricular arrhythmia

ICDs are indicated for patients surviving from life-threatening ventricular arrhythmias.⁵ Two types of ICD, conventional transvenous ICD (TV-ICD) and subcutaneous ICD (S-ICD), can be considered for secondary prevention of SCD.

TV-ICD consists of a pulse generator and a lead attaching the pulse generator to the endocardium via transvenous insertion. In contrast, S-ICD has a pulse generator and a subcutaneous lead tunnelled from the pulse generator to a position along the left parasternal margin. S-ICD has the advantage of avoiding the transvenous lead complications seen with TV-ICD, such as cardiac perforation, cardiac tamponade, pneumothorax and intravascular lead infection.⁵ However, S-ICD should only be considered as an alternative to TV-ICD when pacing therapy for bradycardia, cardiac resynchronization or antitachycardia pacing is not required. As a result, S-ICD is a reasonable alternative in young patients with MVP presenting with ventricular arrhythmias who require concomitant open valvular surgery, since intravascular lead infection can lead to disastrous prosthetic valve endocarditis.    

Treatment of mitral regurgitation in MVP

Since most patients with MVP are asymptomatic and run a benign course, monitoring of symptoms and cardiac function will suffice. Treatment of mitral regurgitation associated with MVP is indicated when there is progression of symptoms, worsening of cardiac function or dilated LV size.⁶

Traditionally, MVP is repaired surgically by partial leaflet resection, annular plication, sliding valvuloplasty, placement of annular ring and folding valvuloplasty, depending on the morphology of the mitral valve. In complicated cases (eg, severe Barlow’s disease), mitral valve replacement remains the last resort.

In recent years, with the development of technology, transcatheter repair has emerged as an option for patients deemed to have prohibitive surgical risk. The MitraClip system, an edge-to-edge leaflet repair device, is increasingly being utilized. Early results showed that with proper patient selection, the transcatheter approach can reduce the severity of mitral regurgitation and reverse LV modelling, improving symptoms and quality of life of patients.⁷