Midventricular hypertrophic cardiomyopathy is a phenotype or morphological variant of asymmetric hypertrophic cardiomyopathy (HCM) characterized by hypertrophy in the midventricular segment that might result in midventricular obstruction.

Epidemiology

Midventricular hypertrophic cardiomyopathy is rare ¹ accounting for up to 4-10% ^2-4.

Association

Midventricular hypertrophic cardiomyopathy in particular with midventricular obstruction is associated with left ventricular apical aneurysms.

Clinical presentation

Symptoms of midventricular hypertrophic cardiomyopathy and midventricular obstruction do not differ significantly from other types of hypertrophic cardiomyopathy or left ventricular outflow obstruction and include performance deficits, dyspnea, angina, presyncope, syncope on exertion ².

On auscultation, there might be an apical systolic murmur like or variably a long mitral diastolic murmur ².

Complications

Complications of midventricular hypertrophic cardiomyopathy include ^1-4:

• myocardial ischemia or myocardial necrosis

• cardiac thrombus formation

• systemic embolism

• ventricular arrhythmias

• sudden cardiac death

Pathology

Midventricular hypertrophic cardiomyopathy is characterized by hypertrophy of the midventricular segments not only of the septum but also the free wall, which can result in midventricular obstruction.

Midventricular obstruction is defined by a peak gradient of ≥30 mmHg of the left ventricular mid cavity ¹. There are apparently significant variations in the size of the obstructed apical cavity ².

This phenotype is typically not associated with obstruction of the left ventricular outflow tract or systolic anterior motion (SAM) of the anterior leaflet of the mitral valve ¹.

Radiographic features

The typical imaging feature of midventricular hypertrophic cardiomyopathy is a dumbell shape or hourglass appearance of the left ventricle, which can be conveniently appreciated on left ventricular long-axis views ¹.

Ultrasound

Echocardiography

Echocardiography can demonstrate the hypertrophied left ventricular segments and can aid in the evaluation of midventricular obstruction defined by a peak mid cavity gradient ≥30 mmHg ^1,4-6.

MRI

Cardiac MRI can show hypertrophy of the midventricular segments and can aid in the evaluation of cardiac volumes and cardiac function and associated myocardial fibrosis and scarring ¹. The following features might be present in midventricular hypertrophic cardiomyopathy ^1,3-7:

• cine imaging

  • confined midventricular wall thickening

  • dumbell or hourglass shape of the left ventricle

  • left ventricular apical aneurysm

  • preserved or increased ejection fraction

• cardiac tissue characterization

  • T1 mapping: increased native T1 values

  • ECV: increased

• IRGE/PSIR:

  • late gadolinium enhancement in midventricular and apical segments

  • indicating replacement fibrosis or myocardial scarring

  • might show complications as apical aneurysms or intracardiac thrombi

Radiology report

The radiological report should include a description of the following ^1-6:

• location and extent of hypertrophic wall segments

• cardiac volumes and measurements including left ventricular mass

• cardiac wall motion abnormalities

• signs of myocardial fibrosis, myocardial scarring or replacement fibrosis

• mitral annular plane systolic excursion (MAPSE)

• complications as apical aneurysms or left ventricular thrombus formation

• mid cavity gradient

Differential diagnosis

Conditions that might mimic the clinical presentation or imaging appearance of asymmetric hypertrophic cardiomyopathy include ^1,4-6:

• left ventricular aneurysm

• apical hypertrophic cardiomyopathy

• asymmetric hypertrophic cardiomyopathy

• mass-like hypertrophic cardiomyopathy

• myocardial infarction