What are the common ECG (electrocardiogram) findings in patients with Congestive Heart Failure (CHF)?

ECG Findings in Congestive Heart Failure

A completely normal ECG makes heart failure, especially with left ventricular systolic dysfunction, highly unlikely and should prompt reconsideration of the diagnosis. 1

Key Diagnostic Principle

• A normal ECG combined with normal natriuretic peptide levels (BNP <35 pg/mL or NT-proBNP <125 pg/mL) essentially excludes heart failure as the cause of symptoms. 1, 2
• Conversely, 75-95% of patients with phenotypic heart failure demonstrate ECG abnormalities, though these do not reliably correlate with severity. 1

Common ECG Abnormalities in Heart Failure

Rhythm Disturbances

• Atrial fibrillation/flutter is one of the most frequent arrhythmias, occurring in approximately 13-14% of heart failure patients and primarily predicting cardiovascular death rather than heart failure hospitalization. 1, 3, 4
• Sinus tachycardia appears in approximately 15-29% of patients and may indicate decompensated heart failure, anemia, fever, or hyperthyroidism requiring clinical assessment. 1, 3
• Ventricular arrhythmias including premature ventricular contractions (18%) and nonsustained ventricular tachycardia are common but do not specifically predict sudden death over other modes of mortality. 1, 3, 5

Conduction Abnormalities

• QRS prolongation ≥120 ms occurs in approximately 16% of patients and indicates electrical dyssynchrony, potentially identifying candidates for cardiac resynchronization therapy. 1, 3
• Left bundle branch block appears in 6% of patients and is associated with increased risk of heart failure hospitalization. 1, 3, 4
• PR interval prolongation >200 ms is present in approximately 22% of patients and may result from medications (beta-blockers, digoxin, antiarrhythmics) or intrinsic conduction disease. 1, 3
• Atrioventricular block may indicate myocardial infarction, drug toxicity, myocarditis, sarcoidosis, or genetic cardiomyopathies requiring pacemaker consideration. 1

Structural and Ischemic Changes

• Left ventricular hypertrophy is detected in 22-24% of patients and suggests hypertension, aortic valve disease, or hypertrophic cardiomyopathy as underlying etiologies. 1, 3
• Pathological Q waves indicate prior myocardial infarction or may appear with hypertrophic cardiomyopathy, left bundle branch block, or pre-excitation patterns. 1
• Myocardial ischemia/infarction patterns warrant immediate troponin measurement, echocardiography, and consideration of coronary angiography. 1

Repolarization Abnormalities

• QTc prolongation occurs in approximately 71% of patients with systolic heart failure and is significantly more pronounced in severe systolic dysfunction (EF ≤35%). 3
• Low QRS voltage combined with ventricular wall thickening creates a diagnostic paradox suggesting infiltrative cardiomyopathy (amyloidosis, sarcoidosis) and warrants cardiac MRI evaluation. 1, 6

Other Findings

• Left axis deviation appears in 42% of patients with systolic heart failure. 3
• Atrial premature contractions occur in approximately 10% of patients. 3

Clinical Implications and Management Algorithms

For patients with abnormal ECG findings:

• Atrial fibrillation/flutter requires rate control, anticoagulation assessment using CHA₂DS₂-VASc score (most heart failure patients score ≥2), and consideration of rhythm control with amiodarone (the only antiarrhythmic safe in systolic heart failure). 1
• QRS ≥120 ms with LBBB morphology identifies candidates for cardiac resynchronization therapy (CRT-P or CRT-D) after echocardiographic confirmation of dyssynchrony. 1
• Ventricular arrhythmias warrant laboratory evaluation for electrolyte abnormalities (hypokalemia, hypomagnesemia), assessment for ischemia, and ICD consideration based on ejection fraction and other risk factors—not based solely on arrhythmia presence. 1, 5

Prognostic Significance

• Any abnormal ECG at baseline significantly predicts worse outcomes in heart failure with preserved ejection fraction (HFpEF), including increased risk of the composite endpoint of cardiovascular death, heart failure hospitalization, and cardiac arrest (HR 1.48). 4
• Bundle branch block specifically predicts heart failure hospitalization (HR 1.33), while atrial fibrillation primarily predicts cardiovascular death (HR 1.57). 4
• The prognostic value of ECG abnormalities emphasizes the importance of not dismissing subtle or nonspecific changes as clinically insignificant. 4

Critical Pitfalls to Avoid

• Do not assume a diagnosis of heart failure is correct if the ECG is completely normal—this combination has <10% probability of systolic heart failure and warrants diagnostic reconsideration. 1, 2
• Do not use ventricular ectopy or nonsustained ventricular tachycardia alone to guide antiarrhythmic therapy or ICD placement, as these findings do not specifically predict sudden death over other mortality modes. 5
• Do not overlook low voltage ECG with ventricular thickening on imaging—this paradoxical finding strongly suggests infiltrative cardiomyopathy requiring cardiac MRI for definitive diagnosis. 1, 6
• Do not attribute all ECG changes to heart failure itself—systematically evaluate for reversible causes including electrolyte abnormalities, drug toxicity, ischemia, thyroid dysfunction, and systemic diseases. 1