Differential diagnosis of tachycardia with a typical left bundle branch block morphology

Table 1 Electrocardiographic QRS morphology criteria favoring ventricular tachycardia over supraventricular tachycardia

Authors	Date	Morphology	Criteria favoring ventricular tachycardia
Wellens et al[2]	1978	RBBB-like	Monophasic R in V1
			qR, QS, RS in V1
			rS, QS, qR in V6
			R/S < 1 in V6 (S > R or QS in V6)
			Left axis deviation
			QRS width > 140 ms
Kindwall et al[3]	1988	LBBB-like	R in V1 or V2 > 30 ms
			Any Q wave in V6
			Onset of QRS to nadir of S ≥ 60 ms in V1 or V2
			Notching of downstroke of S in V1 or V2
Akhtar et al[4]	1988		Positive QRS concordance across the precordium
			Extreme left axis deviation (-90° to ± 180°)
		LBBB-like	Right axis deviation
			QRS > 160 ms
		RBBB-like	QRS > 140 ms
Brugada et al[5]	1991		Absence of RS complex in all precordial leads
			R to S interval > 100 ms in ≥ one precordial lead
			Wellens’ morphologic criteria in leads V1 or V6
Vereckei et al[6]	2008		Initial R wave in lead aVR
			Initial r or q wave > 40 ms in lead aVR
			Notch on descending limb of negative onset, predominantly negative QRS in lead aVR
			vi/vt ≤ 1

vi/vt: Ratio of voltage amplitude during initial 40 ms of QRS complex relative to terminal 40 ms in any lead with a bi- or multiphasic QRS complex; LBBB: Left bundle branch block; RBBB: Right bundle branch block.

Table 2 Differential diagnosis of tachycardia with a typical left bundle branch block QRS morphology

Arrhythmia	ECG and clinical features
SVT with fixed left bundle branch block	LBBB present on baseline ECG
	QRS during tachycardia usually an identical match
SVT with functional LBBB aberrancy	Most often due to orthodromic AVRT
	At rapid rates, QRS alternans may be present
Atriofascicular antidromic tachycardia	Preexcitation may be minimal or absent during sinus rhythm
	Late QRS transition, leftward axis common
	Frequently coexists with other accessory pathways or AV nodal reentry
SVT with bystander atriofascicular accessory pathway	Accessory pathway does not participate in reentrant circuit of orthodromic AVRT, AVNRT, or atrial tachycardias (including atrial fibrillation and flutter)
Bundle branch reentrant ventricular tachycardia	Associated with acquired structural heart disease (cardiomyopathy, valvular disease)
	Prolonged PR interval and nonspecific IVCD often present during sinus rhythm

SVT: Supraventricular tachycardia; AVRT: Atrioventricular reentrant tachycardia; IVCD: Intraventricular conduction defect; AVNRT: Atrioventricular nodal reentrant tachycardia.