What are the implications and management of a widened QRS (Quadrature Amplitude Modulation complex indicating abnormal heart rhythm) complex with two peaks?

Widened QRS Complex with Two Peaks: Differential Diagnosis and Management

Primary Interpretation

A widened QRS complex with two peaks (notching) most commonly represents either right bundle branch block (RBBB) with its characteristic rsr' or rsR' pattern, or ventricular tachycardia (VT), and the immediate priority is determining hemodynamic stability followed by distinguishing between these entities. 1

Initial Assessment Algorithm

Step 1: Hemodynamic Status

• If the patient is hemodynamically unstable, proceed immediately to synchronized DC cardioversion regardless of the underlying mechanism. 2, 1, 3
• Stable vital signs do not help distinguish between supraventricular tachycardia (SVT) and VT. 1

Step 2: Rhythm vs. Conduction Abnormality

Determine if this represents:

• A tachyarrhythmia (heart rate typically >100 bpm requiring urgent diagnosis)
• A baseline conduction abnormality (sinus rhythm with bundle branch block)

Differential Diagnosis of Two-Peaked QRS

Complete Right Bundle Branch Block (RBBB)

The two-peaked pattern is characteristic of RBBB when: 2

• QRS duration ≥120 ms
• rsr', rsR', rSR', or rarely qR pattern in leads V1 or V2, where the R' or r' deflection (second peak) is usually wider than the initial R wave
• S wave of greater duration than R wave or >40 ms in leads I and V6
• Normal R peak time in leads V5 and V6 but >50 ms in lead V1

Ventricular Tachycardia Masquerading as RBBB

If this two-peaked pattern occurs during tachycardia, consider VT when: 2, 1

• History of previous myocardial infarction (strongly suggests VT)
• First occurrence of wide QRS tachycardia after infarction
• RS interval >100 ms from initial R to nadir of S in any precordial lead (highly specific for VT) 2, 4
• Absence of RS complex in all precordial leads (negative concordance—diagnostic for VT) 2, 4

Critical Diagnostic Features During Tachycardia

Signs Diagnostic of VT

• AV dissociation with ventricular rate faster than atrial rate (present in only 30% of VTs but pathognomonic when identified) 2, 1, 3
• Fusion beats (merger of conducted supraventricular impulses with ventricular depolarization—pathognomonic for VT) 3, 5
• QRS width >140 ms with RBBB pattern or >160 ms with LBBB pattern 2, 1
• QR complexes indicating myocardial scar (present in ~40% of post-MI VTs) 2

Absence of RS Complex Rule

• If no RS complex exists in any precordial lead (all positive or all negative deflections), this is diagnostic for VT with 98.7% sensitivity and 96.5% specificity. 4

RS Interval >100 ms Rule

• When RS complexes are present, measure from the beginning of R to the nadir of S wave in precordial leads. 2, 4
• An RS interval >100 ms in any precordial lead is highly specific for VT. 2, 1, 4

Management Algorithm for Wide QRS Tachycardia

For Hemodynamically Stable Patients

When diagnosis is uncertain, treat as VT—this is the safest approach. 1, 3, 5

Pharmacologic Options:

• IV procainamide and/or sotalol for stable wide QRS-complex tachycardia of ventricular origin 1
• Amiodarone for patients with impaired LV function or heart failure 1
• Lidocaine as second-line therapy 1

Critical Pitfall to Avoid:

• Never administer verapamil or diltiazem for wide-complex tachycardia of uncertain etiology—this can cause severe hypotension or accelerated ventricular rate in VT or pre-excited atrial fibrillation. 3

Special Consideration: Pre-excited Tachycardia

If the two-peaked pattern represents antidromic AVRT or atrial fibrillation with Wolff-Parkinson-White (WPW): 2, 6

• The QRS is generally wider (more pre-excited) compared to sinus rhythm
• Adenosine should be used with extreme caution as it may produce ventricular fibrillation in patients with coronary artery disease and rapid ventricular rates in pre-excited tachycardias 2, 3
• Pre-excited tachycardias require alternative approaches and specialist referral 1

Diagnostic Aids

Compare to Baseline ECG

• Obtain previous ECGs during sinus rhythm when available—if the two-peaked pattern matches baseline RBBB morphology, this suggests SVT with pre-existing bundle branch block rather than VT. 3, 5

Lead aVR Analysis

A newer diagnostic approach using lead aVR alone identifies VT when: 5

• Dominant R wave (R or Rs complexes)
• Initial q or r wave duration >40 ms (qR or rS complexes)
• Notch in the descending Q wave limb in a negative complex

Post-Acute Management

After successful termination of wide QRS-complex tachycardia of unknown etiology, refer patients to an arrhythmia specialist. 1

For confirmed WPW syndrome, long-term management options include catheter ablation or drug therapy. 1