How should I manage a 62-year-old man whose stress test electrocardiogram shows left‑axis deviation (QRS axis < ‑30°), incomplete right bundle‑branch block (QRS duration > 90 ms with terminal R wave in V1/V2), and Q‑waves > 40 ms in leads V1‑V4 consistent with an old anteroseptal myocardial infarction of indeterminate age?

Management of 62-Year-Old Man with ECG Showing Left Axis Deviation, Incomplete RBBB, and Old Anteroseptal MI

This patient requires immediate comprehensive cardiac evaluation with echocardiography to assess left ventricular function and wall motion abnormalities, followed by coronary angiography if not previously performed, because the combination of pathologic Q waves in V1-V4 indicates prior anteroseptal myocardial infarction that mandates aggressive secondary prevention and risk stratification. 1, 2

Immediate Diagnostic Priorities

Confirm the Old Myocardial Infarction

• Pathologic Q waves ≥40 ms in V1-V4 meet ACC/AHA criteria for prior anteroseptal myocardial infarction and require urgent evaluation even if the timing is indeterminate. 1, 2

• Verify proper precordial lead placement before attributing findings to pathology, as superior misplacement of V1-V2 electrodes (in 2nd or 3rd intercostal space instead of 4th) can create artifactual poor R-wave progression mimicking anterior infarction. 3

• The presence of Q waves >40 ms duration in two or more contiguous anterior leads (V1-V4) is highly specific for myocardial scar tissue and wall motion abnormalities. 2, 4

Assess Left Ventricular Function Urgently

• Order transthoracic echocardiography immediately to evaluate for segmental wall motion abnormalities (akinesis or dyskinesis) in the anteroseptal territory, measure ejection fraction, and assess for structural complications. 2, 3

• The combination of left axis deviation (<-30°) with conduction abnormalities in the setting of prior MI suggests possible left anterior fascicular block, which does not independently worsen prognosis but indicates more extensive conduction system disease. 1, 5

• If echocardiography shows "grey zone" findings or is non-diagnostic, cardiac MRI with gadolinium should be performed to assess myocardial viability, scar burden, and late gadolinium enhancement. 3

Evaluate the Conduction Abnormalities

Incomplete Right Bundle Branch Block

• The incomplete RBBB (QRS >90 ms with terminal R in V1/V2) meets ACC/AHA criteria and is defined as QRS duration 110-119 ms in adults with rsr' or rsR' pattern in V1-V2. 1

• Incomplete RBBB can represent a benign finding but requires exclusion of structural heart disease including right ventricular enlargement, atrial septal defect (listen for fixed split S2), arrhythmogenic right ventricular cardiomyopathy, and Brugada pattern. 6

• The RSR' complex with wide QRS in the setting of old MI may represent a terminal conduction delay within impaired tissue surrounding the infarct scar—a specific marker of myocardial scar. 4

Left Axis Deviation

• Left axis deviation (QRS axis <-30°) combined with qR pattern in aVL and rS pattern in inferior leads (II, III, aVF) suggests left anterior fascicular block. 1, 5

• In patients with heart failure and LBBB morphology undergoing evaluation, left axis deviation is an independent predictor of worse clinical outcomes (HR 1.40), though this patient has incomplete RBBB, not LBBB. 7

• The combination of left axis deviation with incomplete RBBB creates a bifascicular pattern that warrants monitoring for progression to complete heart block, though immediate pacing is not indicated if asymptomatic. 1

Mandatory Secondary Prevention for Prior MI

Optimize Medical Therapy

• Initiate or verify adherence to guideline-directed medical therapy: high-intensity statin, aspirin (or P2Y12 inhibitor if within 1 year of event), beta-blocker, and ACE inhibitor or ARB. 8

• Beta-blockers are particularly important as they reduce mortality post-MI and help control heart rate if there is underlying left ventricular dysfunction. 8

• If ejection fraction is ≤40% on echocardiography, add aldosterone antagonist (spironolactone or eplerenone) for additional mortality benefit. 8

Risk Stratification for Sudden Cardiac Death

• If echocardiography reveals ejection fraction ≤35% despite optimal medical therapy for ≥3 months (or ≥40 days post-MI), the patient meets criteria for primary prevention ICD evaluation. 9

• The presence of prolonged QRS duration (if ≥170 ms) in the setting of left ventricular dysfunction is associated with significantly reduced ejection fraction (mean 24% vs 36%). 9

• Consider ambulatory ECG monitoring (Holter or event monitor) to screen for ventricular arrhythmias, which would strengthen the indication for ICD. 3

Coronary Revascularization Assessment

• If the patient has not had coronary angiography since the MI, perform it now to define coronary anatomy, assess for multivessel disease, and determine if revascularization (PCI or CABG) is indicated. 1

• Even with an old infarction of indeterminate age, there may be viable myocardium in the infarct territory or significant stenoses in other territories requiring intervention. 1

• Stress testing is contraindicated until you have established baseline ventricular function and ruled out high-risk anatomy requiring urgent revascularization. 1

Common Pitfalls to Avoid

• Do not dismiss the Q waves as artifact without verifying lead placement and obtaining echocardiography—pathologic Q waves in V1-V4 are highly specific for anterior MI scar. 2, 3

• Do not assume incomplete RBBB is benign without excluding structural heart disease, especially atrial septal defect (examine for fixed split S2) and right ventricular pathology. 6

• Do not delay echocardiography waiting for stress test results—the presence of pathologic Q waves mandates immediate structural assessment. 1, 2

• Do not overlook the possibility of peri-infarction block, which occurs when the terminal QRS is widened in the presence of Q waves from old MI, representing conduction delay through scar tissue. 1

Ongoing Management Algorithm

1. Obtain echocardiography within 24-48 hours to measure ejection fraction and assess wall motion. 2, 3

2. If EF ≤40%: Optimize medical therapy, consider cardiac MRI for viability assessment, and plan ICD evaluation if EF ≤35% after 3 months of optimal therapy. 9

3. If EF >40%: Continue guideline-directed medical therapy, perform coronary angiography if not previously done, and consider stress testing for ischemia evaluation once anatomy is defined. 1

4. Monitor for progression of conduction disease with serial ECGs, as the combination of left axis deviation and incomplete RBBB may progress to complete heart block. 1

5. Ensure aggressive risk factor modification: smoking cessation, blood pressure control, diabetes management, and cardiac rehabilitation enrollment. 8