What ECG changes are associated with dilated cardiomyopathy?

ECG Changes in Dilated Cardiomyopathy

The most common ECG changes in dilated cardiomyopathy include left bundle branch block (LBBB), left atrial enlargement, sinus tachycardia, and nonspecific ST-T wave abnormalities, with an abnormal ECG present in nearly 100% of patients. 1

Common ECG Findings in Dilated Cardiomyopathy

Conduction Abnormalities

• Left bundle branch block (LBBB): Present in approximately 41% of patients 1
• Intraventricular conduction delays that worsen as the disease progresses 2
• Prolonged PR interval (first-degree AV block): Found in about 28% of patients 1
• QRS widening (>120 ms) in advanced disease 3

Chamber Enlargement Signs

• Left atrial enlargement: Present in approximately 48% of patients 1
• Voltage criteria for ventricular enlargement that persist despite disease progression 2
• Left ventricular hypertrophy patterns 4

Repolarization Abnormalities

• Anterolateral T-wave inversions (prognostically significant) 4
• Primary ST-T wave changes in about 11% of patients 1
• Prolonged QT interval 3

Other Findings

• Abnormal Q waves (seen in approximately 19% of patients) 1
• Sinus tachycardia, particularly in advanced disease 3
• Leftward shifting of the mean QRS axis with disease progression 1

Prognostic Significance of ECG Findings

ECG abnormalities in dilated cardiomyopathy have important prognostic implications:

• Death from heart failure is independently associated with:

  • Left bundle branch block 5
  • Left atrial enlargement 5
  • Left ventricular hypertrophy 4
  • Increased heart rate 4

• Sudden death or malignant ventricular arrhythmias are predicted by:

  • High-grade ventricular arrhythmias (Lown grade 4A or 4B) 5
  • Prolonged repolarization time (QTc-QRS interval) 5
  • S wave amplitude in V2 and R wave amplitude in lead III 4
  • Anterolateral T-wave inversion 4

ECG Changes vs. Disease Progression

The ECG evolves with disease progression:

• Early disease may show only subtle changes
• As cardiomyopathy advances, there is increasing frequency and severity of intraventricular conduction disturbances 2
• Progressive leftward shifting of the mean QRS axis 1
• Increasing QRS duration 3

Differential Diagnosis Considerations

Several conditions may present with similar ECG findings:

1. Athletic heart syndrome:

   • Unlike DCM, athletes typically show balanced biventricular enlargement
   • Normal or enhanced systolic function
   • Normal diastolic function 6

2. Left-dominant arrhythmogenic cardiomyopathy:

   • May mimic DCM
   • Subepicardial fibrosis on CMR favors arrhythmogenic cardiomyopathy 3

3. Tachycardia-induced cardiomyopathy:

   • Persistent tachyarrhythmia precedes LV dysfunction
   • Improvement in LV function with rate or rhythm control 3

Clinical Implications

• An abnormal ECG may be the first sign of dilated cardiomyopathy in up to 25% of patients 1
• ECG findings correlate with different degrees of myocardial impairment 1
• The addition of comprehensive ECG evaluation to clinical assessment significantly improves prognostic accuracy for both death/transplant and sudden death/arrhythmias 4

Monitoring Recommendations

• 12-lead ECG should be performed in the initial evaluation of suspected dilated cardiomyopathy 3
• 24-48 hour ambulatory ECG monitoring is recommended for risk stratification and to guide management of arrhythmias 3
• Extended monitoring (>24 hours) is indicated for patients with palpitations or lightheadedness 3
• Periodic follow-up ECGs help track disease progression and identify worsening conduction abnormalities 1

Pitfalls and Caveats

• ECG changes alone are not diagnostic of dilated cardiomyopathy and must be correlated with imaging findings
• Some ECG abnormalities (like Q waves) may mimic ischemic heart disease but represent myocardial fibrosis in DCM
• Ectopic arrhythmias and AV blocks may be induced or exacerbated by medications like cardiac glycosides rather than the underlying disease process 2
• ECG voltage criteria for chamber enlargement persist despite progressive cardiosclerosis, potentially masking the severity of the disease 2

By understanding these characteristic ECG patterns, clinicians can better identify, risk-stratify, and monitor patients with dilated cardiomyopathy.