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Mid-ventricular hypertrophic obstructive cardiomyopathy is a rare type of cardiomyopathy that can be accompanied by apical aneurysm. We report the case of a patient who presented with ventricular fibrillation, ST-segment elevation on electrocardiography, and cardiac-enzyme elevation, in the presence of normal coronary arteries. Echocardiography and magnetic resonance imaging showed an hourglass appearance of the left ventricle with an aneurysm in the apex. Left-heart catheterization and continuous-wave Doppler echocardiography revealed a pressure gradient between the apical and basal chambers of the left ventricle. Impaired coronary artery circulation might play a role in the development of mid-ventricular obstruction in patients with mid-ventricular hypertrophic obstructive cardiomyopathy.
Mid-ventricular hypertrophic obstructive cardiomyopathy (HOCM) is characterized by asymmetric left ventricular hypertrophy and by a pressure gradient between basal and apical sites in the left ventricle. Mid-ventricular HOCM in association with an apical aneurysm has rarely been reported.1–7 Herein, we describe a case of mid-ventricular HOCM in association with acute myocardial infarction and a left ventricular apical aneurysm.
A 58-year-old man was transferred from another hospital to the coronary care unit of our hospital because of ventricular fibrillation. For the previous 2 years, he had experienced occasional episodes of unsustained ventricular tachycardia and exertional dyspnea, for which he had been prescribed β-blockers; however, he had discontinued that treatment. At the time of initial medical treatment, he had been diagnosed as having hypertrophic nonobstructive cardiomyopathy in the mid portion of the interventricular septum.
After successful defibrillation, the patient's electrocardiogram showed obvious ST-segment elevation in leads V3 through V6 (Fig. 1). Laboratory findings before defibrillation showed that creatine kinase was 1,278 U/L (normal, 55–170 U/L), creatine kinase-MB was 48 U/L (normal, <25 U/L), troponin T was 0.3 ng/mL (normal, <0.1 ng/mL), and myoglobin was 1,250 ng/mL (normal, 60 ng/mL). Other laboratory findings included total cholesterol of 244 mg/dL, low-density lipoprotein cholesterol of 175 mg/dL, and triglycerides of 146 mg/dL. Chest radiography did not show cardiomegaly or pulmonary congestion. Having made a provisional diagnosis of acute myocardial infarction, we performed coronary angiography and found normal coronary arteries. Left ventriculography disclosed a pressure gradient of 71 mmHg between apical and basal sites within the left ventricle. Echocardiography (Fig. 2A) disclosed asymmetric septal hypertrophy (the end-diastolic thickness of the septum was 25 mm, compared with 10 mm for the posterior wall), mid-ventricular obstruction during systole, and an apical aneurysm. Continuous-wave Doppler echocardiography (Fig. 2B) revealed a peak flow velocity of 4.0 m/sec in early systole, which corresponded to a pressure gradient of 64 mmHg between the apical and basal sites of the left ventricle. There was paradoxical jet flow from the apical aneurysm to the left ventricular outflow tract during early diastole (Fig. 2B, arrows).8 201-Thallium single-photon emission computed tomography (Fig. 3) showed a fixed defect in the left ventricular apex, which indicated infarction without viable myocardium. It also showed mid-ventricular obstruction in both vertical and horizontal projections. Electrocardiography-gated, cine magnetic resonance imaging was performed by means of an Intera Achieva 1.5 Tesla (Philips Medical Systems Nederland BV; Best, The Netherlands) using a steady-state coherent sequence, which showed mid-ventricular obstruction and an apical aneurysm on long-axis and 4-chamber images and asymmetric septal hypertrophy on short-axis images. There was a thin-layered, low-signal mass in the apex, suggesting a mural thrombus (Fig. 4). Percutaneous transluminal septal myocardial ablation and implantation of a cardioverter-defibrillator were recommended, but these procedures were not performed because of the patient's refusal. After treatment with an oral β-blocker, the patient experienced no episodes of ventricular tachycardia or exertional dyspnea, but his electrocardiographic and wall-motion abnormalities persisted during the 6-month follow-up period (Figs. 5 and and6,6, respectively).
Mid-ventricular HOCM is a rare form of hypertrophic cardiomyopathy that is often accompanied by an apical aneurysm.1–7 The pathogenesis of myocardial necrosis remains unknown, but it has been suggested that apical aneurysm may be secondary to the increased afterload and high apical pressure arising from the mid-ventricular obstruction seen in the degenerative process of hypertrophic cardiomyopathy.9,10 Other proposed causes of aneurysm formation are small-vessel disease with decreased coronary flow reserve, squeezing of the coronary artery due to the increased wall stress in the hypertrophic myocardial segment, decreased coronary perfusion pressure due to mid-ventricular obstruction, coronary artery spasm, and decreased capillary myocardial fiber ratio.11–13 However, because our patient displayed elevations of cardiac enzymes in the acute phase of his illness, we infer that the apical aneurysm had its origin in an acute coronary artery event, such as mechanical compression of the coronary artery or coronary microcirculation by increased pressure overload and systolic myocardial wall stress associated with an acutely developed mid-ventricular obstruction. In fact, Mohiddin and Fananapazir14 found systolic compression of the epicardial and intramural coronary arteries on angiography in 23 (40%) of 57 consecutive patients who had hypertrophic cardiomyopathy. Although conventional coronary angiography yielded normal results in our patient, it is still possible that acute coronary artery obstruction arose from microthrombosis of a ruptured atherosclerotic plaque or via some other mechanism, which in turn resulted in apical-aneurysm formation and subsequently in accelerated mid-ventricular obstruction caused by increased wall stress on the hypertrophic segments.
Management of mid-ventricular HOCM is unclear, but failure to intervene can result in fatal ventricular arrhythmias4 and sudden death.6 β-Blockers are the 1st choice of treatment in patients with HOCM,15 but the treatment for mid-ventricular HOCM has not yet been established. Dual-chamber pacing16 and percutaneous myocardial ablation7,17 have been proposed as nonsurgical treatments for mid-ventricular HOCM, but long-term benefits and the procedural safety of these options await further observations in large patient populations.
Address for reprints: Yuichi Sato, MD, Department of Cardiology, Nihon University School of Medicine, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8309, Japan. E-mail: pj.ca.u-nohin.dem@sihciuy