What are the ECG findings in patients with Dilated Cardiomyopathy (DCM)?

ECG Findings in Dilated Cardiomyopathy (DCM)

The electrocardiogram (ECG) in dilated cardiomyopathy is abnormal in nearly 100% of cases and may show characteristic findings including left bundle branch block, T-wave inversions, left atrial enlargement, and low voltage QRS complexes. 1

Common ECG Abnormalities in DCM

• Left Bundle Branch Block (LBBB): Present in approximately 30-40% of DCM patients and is the second most common ECG finding. LBBB represents dyssynchronous left ventricular activation and is often associated with more advanced disease 1, 2

• T-wave inversions: Commonly seen in the lateral and inferior leads, representing repolarization abnormalities 1

• Intraventricular conduction defects: Widened QRS complexes (>110 ms) are frequently observed, even without complete bundle branch block 1

• Left atrial enlargement: Present in approximately 47.5% of patients, reflecting the hemodynamic consequences of LV dysfunction 3

• Prolonged PR interval: First-degree AV block is seen in about 27.5% of cases 3

• Abnormal Q waves: Present in approximately 15-19% of patients, particularly in the inferior and/or lateral leads, which may be confused with prior myocardial infarction 1, 3

• Low voltage QRS complexes: Particularly common in advanced disease 1, 4

• Fragmented QRS complexes: A marker of depolarization abnormality associated with arrhythmic events and intraventricular dyssynchrony 2

Specific ECG Patterns in DCM

• Predominant S waves in V2-V4: This is the most frequent characteristic pattern (34.4% of cases), often coexisting with lack of R wave progression from V1 to V4 4

• QS pattern with elevated ST segments: Present in approximately 15.5% of cases, betraying extensive areas of fibrosis or necrosis, typically located at the apex and associated with ventricular tachycardia 4

• Normal QRS shape with ST-T abnormalities: Seen in about 12.2% of cases, showing that repolarization is highly sensitive to alterations in the subendocardial layers 4

Genotype-Specific ECG Findings

• Lamin A/C mutations: Often present with first-degree AV block and pathological Q waves in the inferior and/or lateral leads 1

• Dystrophin mutations: May show similar ECG patterns to Lamin A/C mutations with conduction abnormalities 1

Arrhythmias in DCM

• Ventricular arrhythmias: Present in approximately 30% of DCM patients, even with only mildly dilated LV cavity 1

• Atrial arrhythmias: Supraventricular tachycardias are common, especially in advanced disease 1

• Sinus tachycardia: A common finding, particularly in later stages of the disease 1

Prognostic Implications

• QRS duration: Prolonged QRS duration is associated with worse outcomes and higher mortality 2

• Left ventricular conduction delays: Associated with worse prognosis 3

• QT dispersion: Can identify patients at greatest risk for cardiac death 1

Examples of DCM ECG Patterns

1. Classic DCM pattern: LBBB with poor R wave progression, left axis deviation, and nonspecific ST-T wave changes 1

2. Early DCM: May show only subtle changes such as nonspecific ST-T wave abnormalities with normal QRS duration 5

3. Advanced DCM: Low voltage QRS complexes, LBBB, left atrial enlargement, and frequent ventricular ectopy 3, 4

Clinical Implications

• ECG abnormalities may precede overt structural changes and can be the first sign of disease in approximately 25% of cases 3

• Serial ECG changes, particularly increasing left ventricular conduction delay and leftward shifting of the QRS axis, may indicate disease progression 3

• The presence of specific ECG patterns may help identify genetic subtypes of DCM, particularly in familial cases 1, 5

• ECG findings should be interpreted in conjunction with imaging studies (echocardiography, cardiac MRI) for comprehensive evaluation 1

Monitoring Recommendations

• All DCM patients should have an initial cardiac evaluation with ECG at diagnosis 1

• Asymptomatic DCM patients <10 years of age should have ECG evaluation every 2 years, increasing to annual evaluation after age 10 1

• Patients with LV dysfunction, dilation, or arrhythmias should be reevaluated at least annually 1

• Ambulatory ECG monitoring is recommended for risk stratification, particularly in patients with LVEF <30-35% or age ≥17 years 1