Burned-out phase of hypertrophic cardiomyopathy

The burned-out phase of hypertrophic cardiomyopathy refers to the end-stage of hypertrophic cardiomyopathy and is characterized by myocardial fibrosis, systolic dysfunction and left ventricular wall thinning.

Epidemiology

The burned-out phase can be seen in 3-5% of patients with hypertrophic cardiomyopathy ^1-3.

Diagnosis

In patients with a known diagnosis of hypertrophic cardiomyopathy the burned-out phase can be made by the development of systolic dysfunction (left ventricular ejection fraction <50%) ^1-4.

In patients in which the clinical history of hypertrophic cardiomyopathy is not known, this is a diagnosis of exclusion ¹.

Clinical presentation

Patients with burned-out or end-stage hypertrophic cardiomyopathy may present with variable symptoms including palpitations,  dyspnea on exertion, syncope or cardiac arrest ¹.

Complications

Complications of burned-out phase hypertrophic cardiomyopathy include ^1-5:

• atrial fibrillation
• thromboembolic events
• progressive heart failure
• ventricular tachyarrhythmias
• sudden cardiac death

Pathology

The late stages of hypertrophic cardiomyopathy are characterized by progressive adverse cardiac remodeling and myocardial fibrosis leading to the following features ^1-4:

• decreased contractility and impaired systolic function
• decreased wall-thickness and wall-thinning
• increased end-systolic dimensions
• the disappearance of left ventricular gradients

Subtypes

Hypertrophic cardiomyopathy can progress to the following burned-out phase subtypes ^1,3:

• dilated form with left ventricular dilation
• restrictive form with atrial dilation

Radiographic features

Imaging findings at this stage are heterogeneous and can be non-specific, the cardiac wall might not be thickened and hypertrophic anymore but dilated and thin or might show a mixture of thickened and thinned wall elements ^1-4.

Echocardiography

Echocardiography serves as a first-line method. It will reveal both diastolic and systolic dysfunction ^1,5 and might show a decrease in left ventricular gradients. It might be the only available method in unstable patients or those in critical clinical condition ¹.

MRI

Cardiac MRI will reveal cardiac dysfunction and extensive late gadolinium enhancement indicating replacement fibrosis or myocardial scarring ^1,3-7.

• cine imaging
  • wall motion abnormalities
  • decreased ejection fraction
• cardiac tissue characterization
  • T1 mapping: increased native T1 values
  • ECV: increased
• IRGE/PSIR:
  • diffuse and extensive late gadolinium enhancement
  • might show complications as intracardiac thrombi

Radiology report

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

• cardiac volumes and measurements including left ventricular mass
• cardiac wall motion abnormalities
• the extent of myocardial fibrosis and myocardial scarring 
• complications as intracardiac thrombus formation

Treatment and prognosis

Not unexpected the burned-out phase features an unfavorable outcome with increased mortality of approximately 10-12% per year due to thromboembolic complications, progressive heart failure and an increased incidence of sudden cardiac death ¹. Diffuse and extensive myocardial fibrosis visualized by late gadolinium enhancement (>15% wall mass) is associated with an increased risk of sudden cardiac death ⁸.

Management comprises pharmacotherapy including ACE inhibitors, β-blockers and diuretics. Patients might also benefit from an implantable cardioverter-defibrillator especially in the setting of concomitant arrhythmia. Cardiac transplantation might be considered as definite therapy at this stage ^1,3.

Differential diagnosis

Conditions that might mimic the clinical presentation or imaging appearance of burned-out phase hypertrophic cardiomyopathy include ^1,5-7:

• dilated cardiomyopathy
• cardiac amyloidosis
• cardiac sarcoidosis
• hypertensive cardiomyopathy
• MINOCA