INTRODUCTION

Myasthenia Gravis (MG) is an autoimmune disorder which affects the neuromuscular system. It is estimated to affect more than 700,000 people with incidence from 0.3-2.8 per 100,000 worldwide.¹ It results from decreased number of active acetylcholinesterase receptors at the neuromuscular junction by either destruction or functional block of the receptors by circulating antibodies.² Signs and symptoms include diplopia, body weakness and dyspnea with severity of the disease dependent on the group of muscles involved. It follows a slow progressive course that becomes generalized and may become fatal when respiratory muscles fail.¹ On the other hand, ruptured chordae tendineae is a common cause of mitral valve incompetence leading to acute mitral valve regurgitation.³ The combination of MG and mitral valve disease is a rare occurrence which may preclude a catastrophe, especially during cardiac surgery as definitive treatment for ruptured chordae tendinae.⁴ The decision to proceed with cardiac surgery among these patients is a serious medical dilemma since life-threatening complications are often encountered among post-thymectomy patients with Myasthenia Gravis. This paper presents a rare case of ruptured chordae tendinea with flail leaflet in a post thymectomy patient diagnosed of MG who underwent successful minimally invasive cardiac surgery.

CASE

At the emergency room, patient was in distress with initial vital signs of BP 100/60mmHg, HR 80bpm, RR 34cpm, afebrile, 80% at room air. Physical examination revealed distended neck veins, bibasal crackles, regular cardiac rhythm with holosystolic murmur at the apex 3-4/6 severity, no S3 or S4 gallop with grade 2 pitting bipedal edema. No improvement was noted with 15 LPM oxygen support hence, patient was hooked to Bilevel Positive Airway Pressure (BPAP). 12-lead electrocardiogram showed regular sinus rhythm with left atrial and left entricular hypertrophy, NT pro-BNP was 748 pg/ml (< 125 pg/ml), chest Xray showed bilateral pleural effusion, bilateral pneumonia with pulmonary congestion, COVID-19 RT PCR revealed negative. The patient was managed as decompensated heart failure secondary to possible torn chordae tendineae and was started with diuretics and nitrates for heart failure and broad-spectrum antibiotics for pneumonia. Neurology referral was facilitated and continued Pyridostigmine at 60mg/tab, 1 tab thrice daily. During admission, transthoracic 2D-echocardiogram showed anterior mitral valve prolapse with flail with severe mitral regurgitation, dilated left ventricle with normal systolic function, left ventricular end systolic diameter of 35mm, biatrial dilatation and systolic pulmonary artery pressure of 43mmHg. Transesophageal echocardiogram further revealed prolapsed A1, P1 and anterolateral commissure with flail P1 scallop and an echogenic density attached to posterior leaflet likely a torn cord (Figure 1). Plan of management was minimally invasive mitral valve replacement and the patient was counselled well on the course of surgery and possible complications that may be encountered due to preexisting medical conditions.