Management of Patients with QRS Duration >120 ms
The management of patients with QRS duration exceeding 120 ms should focus on identifying the underlying cause, assessing for cardiac conduction disorders, and implementing appropriate interventions based on the specific conduction abnormality and associated symptoms.
Identification and Classification
A QRS duration >120 ms indicates one of several possible conduction abnormalities 1:
Complete Right Bundle Branch Block (RBBB):
- QRS ≥120 ms
- rSR' pattern in V1/V2 (R' wider than initial R wave)
- S wave duration > R wave or >40 ms in leads I and V6
- Normal R peak time in V5/V6 but >50 ms in V1
Complete Left Bundle Branch Block (LBBB):
- QRS ≥120 ms
- Broad notched/slurred R wave in leads I, aVL, V5, V6
- Absent Q waves in leads I, V5, V6
- R peak time >60 ms in V5/V6
- ST and T waves typically opposite to QRS direction
Nonspecific Intraventricular Conduction Delay:
- QRS >110 ms without meeting RBBB or LBBB criteria
Diagnostic Evaluation
12-lead ECG: Determine specific pattern (RBBB, LBBB, or nonspecific delay)
Echocardiography: Essential to assess:
- Left ventricular function (LVEF)
- Regional wall motion abnormalities
- Structural heart disease
- Evidence of mechanical dyssynchrony
Laboratory testing:
- Electrolytes (particularly potassium)
- Cardiac biomarkers
- Thyroid function tests
Additional testing based on clinical suspicion:
- Cardiac MRI (to evaluate for myocardial scarring)
- Coronary angiography (if ischemia suspected)
- Electrophysiology study (if conduction system disease suspected)
Management Strategy
1. Asymptomatic Patients with Isolated Conduction Abnormality
- Regular follow-up with serial ECGs to monitor for progression
- No specific therapy required if no underlying structural heart disease
- Evaluate for potential causes (ischemia, cardiomyopathy)
2. Patients with Heart Failure and Wide QRS
For patients with heart failure (NYHA class II-IV), LVEF ≤35%, and QRS ≥120 ms:
Cardiac Resynchronization Therapy (CRT) is indicated 1:
- Particularly beneficial in LBBB pattern
- CRT with defibrillator capability (CRT-D) for appropriate candidates
- Improves symptoms, reduces hospitalizations, and decreases mortality
Medication optimization:
- Guideline-directed medical therapy for heart failure
- ACE inhibitors/ARBs
- Beta-blockers
- Mineralocorticoid receptor antagonists
- SGLT2 inhibitors
3. Patients with High-Degree AV Block and Wide QRS
- Permanent pacemaker implantation for:
- Third-degree (complete) AV block
- Advanced/high-grade AV block
- Symptomatic Mobitz type II second-degree AV block
4. Patients with Wide QRS and Ventricular Arrhythmias
- ICD implantation for:
- Primary prevention in patients with LVEF ≤35% despite optimal medical therapy
- Secondary prevention after cardiac arrest or sustained ventricular tachycardia
- Consider if fragmented QRS present with structural heart disease 2
Special Considerations
QRS duration ≥200 ms: Associated with higher defibrillation thresholds in ICD patients 3
Mechanical dyssynchrony: Present in approximately 70% of heart failure patients with wide QRS 3
Fragmented QRS: Associated with myocardial scarring and increased arrhythmic risk, requiring closer monitoring 4, 2
Follow-up Recommendations
- Regular ECG monitoring to assess for progression of conduction disease
- Echocardiographic follow-up in patients with structural heart disease
- Device checks for those with implanted devices (pacemakers, ICDs, CRT)
- Optimization of medical therapy for underlying conditions
Pitfalls to Avoid
- Don't assume all wide QRS complexes are bundle branch blocks - nonspecific intraventricular conduction delays are common
- Don't rely solely on QRS duration for CRT selection - mechanical dyssynchrony assessment improves patient selection
- Don't overlook potentially reversible causes of QRS prolongation (electrolyte abnormalities, medication effects)
- Don't miss the opportunity for sudden cardiac death risk assessment in patients with wide QRS and structural heart disease