What is the significance and management of a notched QRS (electrocardiogram abnormality) at downslope in an electrocardiogram, particularly in older adults or individuals with pre-existing heart conditions?

Notched QRS at Downslope: Clinical Significance and Management

A notched QRS complex on the downslope represents a terminal QRS abnormality that requires immediate evaluation with echocardiography to exclude underlying structural heart disease, particularly cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy (ARVC), or prior myocardial infarction. 1

Understanding Terminal QRS Notching

Terminal QRS notching refers to a low-frequency deflection at the end of the QRS complex, appearing as an abrupt change in the slope of the terminal QRS deflection. 1 This finding differs from:

• Epsilon waves: Terminal notches specifically in anteroseptal precordial leads (V1-V3) associated with ARVC 1
• Fragmented QRS (fQRS): Various RSR' patterns with notching of S or R waves in ≥2 contiguous leads corresponding to coronary territories, associated with myocardial scar 2
• Early repolarization patterns: J-point elevation with terminal QRS slurring or notching, which has different clinical implications 1

Clinical Significance by Context

In Athletes

• Terminal QRS notching with QRS duration >120 ms is uncommon (<2% of athletes) and represents a potential marker of serious cardiovascular disease 1
• Localized QRS prolongation (>110 ms) in right precordial leads (V1-V3) with terminal notching or "epsilon wave" is an ECG marker for ARVC 1
• Complete bundle branch block patterns with notching warrant comprehensive cardiac evaluation including exercise testing, 24-hour ECG monitoring, and cardiac imaging 1

In Coronary Artery Disease

• Fragmented QRS with terminal notching is an independent predictor of cardiac events (myocardial infarction, need for revascularization, or cardiac death) in patients with known or suspected CAD 2
• The presence of fQRS shows significantly lower event-free survival for cardiac events (P <0.001) on long-term follow-up 2
• Terminal notching may indicate myocardial scar from prior infarction, even in the absence of pathological Q waves 2, 3

In Heart Failure

• QRS notching in patients with heart failure and prolonged QRS duration (>120 ms) is associated with interventricular mechanical delay 4
• However, QRS notch itself is not an independent predictor of mechanical dyssynchrony beyond the effect of QRS duration 4

Mandatory Evaluation Algorithm

Step 1: Initial Assessment

• Verify lead placement and repeat ECG if notching is isolated to V1-V2 1
• Measure QRS duration accurately using age-appropriate normal values 1, 5:
  • Adults: Normal <120 ms 1, 5
  • Children 4-16 years: Normal <100 ms 5
  • Children <4 years: Normal <90 ms 5

Step 2: Determine Pattern Recognition

• ARVC pattern: Terminal notching in V1-V3 with QRS >110 ms 1
• Fragmented QRS: RSR' patterns with notching in ≥2 contiguous leads corresponding to coronary territories 2
• Bundle branch block: Complete LBBB or RBBB patterns with notching 1, 6

Step 3: Risk Stratification

High-risk features requiring urgent evaluation:

• QRS duration ≥140 ms (profound non-specific intraventricular conduction delay) 1
• Complete left bundle branch block (QRS ≥120 ms with broad notched R waves in I, aVL, V5-V6) 1, 6
• Terminal notching in V1-V3 suggesting ARVC 1
• Symptoms: syncope, palpitations, family history of sudden cardiac death 1

Step 4: Mandatory Testing

All patients with terminal QRS notching require:

• Echocardiography to evaluate for cardiomyopathy, ventricular dysfunction, or structural abnormalities 1
• 12-lead ECG analysis for pathological Q waves (Q/R ratio ≥0.25 or ≥40 ms duration) 1

Additional testing based on findings:

• Cardiac MRI with contrast if echocardiogram is normal but high clinical suspicion remains, or if ARVC is suspected 1
• Exercise stress testing in patients ≥30 years with risk factors for CAD or suspected prior myocardial infarction 1
• 24-hour ambulatory ECG monitoring if bundle branch block or conduction abnormalities are present 1

Age-Specific Considerations

In Neuromuscular Disease Patients

• Terminal QRS notching with widening (QRS ≥120 ms) occurs in 21% of Duchenne muscular dystrophy patients 1
• Characteristic findings include prominent Q waves in inferolateral leads (I, aVL, V5-V6 or II, III, aVF, V5-V6) with QRS widening 1
• Annual cardiac evaluation with ECG and imaging is mandatory starting at age 10 years 1

In Older Adults

• Terminal notching with complete LBBB is very rare in healthy individuals and strongly suggests underlying structural cardiovascular disorder 1
• May represent early manifestation of ischemic heart disease or cardiomyopathy, appearing years before structural changes are detectable 1

Critical Pitfalls to Avoid

• Do not dismiss terminal QRS notching as benign without structural evaluation, even in asymptomatic patients 1
• Do not confuse incomplete bundle branch block (QRS 110-119 ms) with normal variants 1, 5
• Do not overlook age-dependent QRS duration criteria when evaluating children 5
• Do not attribute terminal notching to athletic heart without excluding ARVC and cardiomyopathy first 1

When No Further Testing is Needed

If echocardiography is completely normal, there are no other concerning clinical findings or ECG abnormalities, and the patient is asymptomatic with no family history of sudden cardiac death, no additional testing is generally necessary. 1 However, maintain clinical surveillance as structural disease may develop over time. 1