What are the typical ECG findings in patients with dilated cardiomyopathy (DCM)?

ECG Findings in Dilated Cardiomyopathy

The most common ECG findings in dilated cardiomyopathy (DCM) include left ventricular hypertrophy, nonspecific ST-T wave changes, sinus tachycardia, QRS widening (>120 ms), and left bundle branch block. 1, 2

Common ECG Abnormalities

Conduction Abnormalities

• Left bundle branch block (LBBB) - Present in approximately 41% of DCM patients 3
• QRS widening >120 ms - Indicates intraventricular conduction disturbances and is associated with disease progression 2
• Prolonged PR interval - Observed in about 27.5% of patients 3
• Prolonged QT interval - Common finding associated with increased arrhythmia risk 2

Rhythm Abnormalities

• Sinus tachycardia - Particularly prevalent in advanced disease, reflecting increased sympathetic tone 2
• Atrial tachyarrhythmias - May require further evaluation with 24-hour ECG monitoring 1
• Ventricular arrhythmias - May be present even without significant LV dysfunction 1

Morphological Changes

• Left atrial enlargement - Present in approximately 47.5% of DCM patients 3
• Abnormal Q waves - Found in about 18.7% of patients 3
• T-wave inversions - Particularly in anterolateral leads, associated with worse prognosis 4
• Low voltage QRS complexes - May be present in some DCM patients 1

Prognostic Significance

ECG abnormalities in DCM have important prognostic implications:

• Increasing QRS duration is a hallmark of disease progression 2
• Left ventricular conduction delays are associated with worse prognosis 3
• Anterolateral T-wave inversion is an independent predictor of death/heart transplant and sudden cardiac death 4
• QT dispersion can identify patients at greatest risk for cardiac death 1

Evaluation Approach

When evaluating ECGs in suspected or confirmed DCM:

1. Initial assessment should include a standard 12-lead ECG as part of the diagnostic workup 2
2. Ambulatory ECG monitoring (24-48 hours) is recommended for:
   • Risk stratification
   • Detection of arrhythmias
   • Patients with symptoms like palpitations or lightheadedness 2
3. Serial ECG monitoring to detect progression of conduction abnormalities, particularly leftward shifting of QRS axis and increasing left ventricular conduction delay 3

Clinical Pearls and Pitfalls

• ECG abnormalities may be present in 100% of DCM patients, making it a sensitive (though not specific) tool for detection 3
• In some cases (25%), ECG abnormalities may be the first sign of disease 3
• The presence of ECG abnormalities does not correlate well with the severity of skeletal muscle involvement in neuromuscular diseases associated with DCM 1
• ECG findings should be interpreted in conjunction with imaging studies (echocardiography, cardiac MRI) for comprehensive evaluation 1

Differential Considerations

When interpreting ECG changes in suspected DCM, consider:

• Athletic heart syndrome - Shows balanced biventricular enlargement with normal/enhanced systolic function 2
• Left-dominant arrhythmogenic cardiomyopathy - May mimic DCM but typically has subepicardial fibrosis on CMR 2
• Tachycardia-induced cardiomyopathy - Characterized by persistent tachyarrhythmia preceding LV dysfunction 2

ECG remains an accessible, reproducible, and cost-effective tool that provides valuable diagnostic and prognostic information in DCM patients, with systematic evaluation having incremental impact on risk stratification 4.