What causes an apical cap aneurysm?

Causes of Apical Cap Aneurysm in Hypertrophic Cardiomyopathy

Apical cap aneurysm in hypertrophic cardiomyopathy is primarily caused by myocardial ischemia and infarction resulting from microvascular dysfunction, even in the absence of epicardial coronary artery disease. 1

Primary Pathophysiologic Mechanisms

1. Myocardial Ischemia

• Oxygen Supply-Demand Mismatch

  • Myocardial hypertrophy increases oxygen demand
  • Microvascular dysfunction with impaired coronary flow reserve reduces oxygen supply 1
  • Medial hypertrophy and reduced density of intramural arterioles limit perfusion 1

• Exacerbating Factors

  • Hyperdynamic systolic function increases oxygen demand
  • High intracavitary pressures from LVOT obstruction further compromise perfusion 1
  • Midventricular obstruction can specifically contribute to apical ischemia 1

2. Structural and Hemodynamic Contributors

• Regional Wall Stress

  • Cavity obliteration up to the midventricular level creates abnormal stress patterns 2
  • Areas of myocardial fibrosis become susceptible to aneurysm formation 3

• Progressive Remodeling

  • Initial ischemic injury leads to fibrosis
  • Fibrotic tissue replaces normal myocardium in the apex 2
  • Dyskinetic or akinetic segments develop in the most distal portion of the LV 1

Diagnostic Features and Identification

Imaging Characteristics

• Defined as a discrete thin-walled dyskinetic or akinetic segment of the most distal portion of the LV chamber 1
• Often associated with transmural scar or late gadolinium enhancement (LGE) on CMR imaging 1
• Independent of size, but represents a distinct morphological abnormality 1

Detection Methods

• CMR imaging is particularly valuable for detection of apical aneurysms that may be missed by echocardiography 1
• Late gadolinium enhancement on CMR helps identify associated myocardial fibrosis and scarring 1

Clinical Significance

Risk Implications

• Apical aneurysms are associated with increased risk of:

  • Sudden cardiac death
  • Heart failure progression
  • Ventricular arrhythmias
  • Thromboembolic events including stroke 1

• Considered an independent risk factor for adverse outcomes in HCM 1

Prevalence

• Occurs in approximately 2% of patients with HCM 1
• May be underrecognized without appropriate imaging techniques 1

Distinguishing Features from Other Aneurysm Types

Unlike post-myocardial infarction aneurysms that result from epicardial coronary artery occlusion, apical aneurysms in HCM develop despite normal coronary arteries due to microvascular dysfunction and regional ischemia 2.

Clinical Management Implications

The presence of an apical aneurysm should prompt consideration of:

• Anticoagulation to prevent thromboembolic events 4
• ICD implantation for primary prevention of sudden cardiac death 1
• Potential catheter ablation for associated ventricular arrhythmias 4, 3

Understanding the pathophysiology of apical aneurysm formation is crucial for risk stratification and management decisions in patients with HCM.