What does a slurred upstroke after the QRS (electrocardiogram complex) on an ECG (electrocardiogram) indicate?

Slurred Upstroke After QRS: Early Repolarization Pattern

A slurred upstroke after the QRS complex represents a terminal QRS slur, which is a component of early repolarization pattern (ERP) and is defined as an abrupt change in the slope of the last deflection at the end of the QRS complex. 1

Definition and ECG Characteristics

Terminal QRS slur is formally defined by the American Heart Association as an abrupt change in the slope of the last deflection at the end of the QRS, distinguishing it from a terminal QRS notch (which is a discrete low-frequency deflection). 1

• The J point (junction between QRS and ST segment) should be measured at the onset of the slur when present 1
• This finding falls under the umbrella term "early repolarization pattern" (ERP), which can include ST-segment elevation without chest pain, terminal QRS slurring, or terminal QRS notching 1
• The slur is considered part of the QRS complex itself, though debate exists about this classification 1

Clinical Significance and Risk Stratification

While historically considered a benign normal variant with prevalence up to 10% in the general population, terminal QRS slurring has been associated with increased risk of idiopathic ventricular fibrillation and sudden cardiac arrest since the landmark 2008 Haïssaguerre study. 1, 2

Risk Assessment Factors:

• High-risk features include: syncope, palpitations, family history of sudden cardiac death, or documented arrhythmias 2
• The pattern resembles Brugada syndrome in arrhythmogenicity under certain conditions 1
• Survivors of idiopathic sudden cardiac arrest demonstrate terminal QRS slurring at significantly higher frequency than controls 1

Important Distinctions:

• Differentiate from Brugada pattern: Brugada shows downward coved or saddleback ST-segment elevations in leads V1-V3, associated with sudden cardiac death 1, 2
• Differentiate from epsilon waves: These are low-frequency terminal QRS deflections in anteroseptal precordial leads seen in arrhythmogenic right ventricular cardiomyopathy 1, 2
• Differentiate from fragmented QRS: Multiple notches (>2) on R or S waves in contiguous leads suggest myocardial scar with high specificity (92.5%) and are associated with increased mortality 3

Recommended Evaluation Algorithm

For asymptomatic patients with isolated terminal QRS slur and no high-risk features, no immediate intervention is required, but documentation and awareness are essential. 2

Step 1: Clinical Assessment

• Assess for symptoms: syncope, palpitations, chest pain, or lightheadedness 2
• Obtain family history of sudden cardiac death or cardiomyopathy 2
• Review for other ECG abnormalities suggesting specific cardiac pathology 2

Step 2: Risk-Based Testing

If high-risk features present:

• Echocardiogram to assess structural heart disease and ventricular function 4
• Ambulatory ECG monitoring (24-48 hours) if arrhythmias suspected 4, 2
• Consider electrophysiology consultation for risk stratification 2

If low-risk (asymptomatic, no family history):

• Compare with prior ECGs if available 2
• Document finding for future reference 2
• Routine follow-up without additional testing 2

Common Pitfalls to Avoid

• Misinterpreting technical artifacts as true QRS slurring—ensure proper lead placement and ECG quality 2
• Failing to distinguish between benign early repolarization and pathological patterns like Brugada syndrome or epsilon waves 2
• Overlooking associated findings: Check for J-point elevation ≥1 mm, which when present with inferior or lateral lead distribution may increase risk 1
• Confusing with ischemic changes: In older patients or those with cardiac risk factors, QRS notching/slurring can indicate myocardial scar with 93.8% specificity for ischemic heart disease 5

Context-Specific Considerations

In patients with known or suspected coronary artery disease, terminal QRS slurring has different implications—it may represent myocardial scar rather than benign early repolarization, with sensitivity of 62.2% and specificity of 93.8% for ischemic heart disease. 5 In this population, echocardiography and stress testing are warranted. 4