» Articles » Differential Diagnosis Of Wide QRS Tachycardias Differential Diagnosis Of Wide QRS Tachycardias Demosthenes G Katritsis Josep Brugada Login or register to view PDF. Order reprints Abstract In this article, the authors discuss the differential diagnostic methods used in clinical practice to identify types of wide QRS tachycardias (QRS duration >120 ms). A correct diagnosis is critical to management, as misdiagnosis and the administration of drugs usually utilised for supraventricular tachycardia can be harmful for patients with ventricular tachycardia. Keywords Tachycardias, supraventricular tachycardia, ventricular tachycardia Disclosure The authors have no conflicts of interest to declare. Correspondence Demosthenes Katritsis, Hygeia Hospital, 4 Erythrou Stavrou St, Athens 15123, Greece; E: [email protected] Received date 28 April 2020 Accepted date 27 May 2020 Citation Arrhythmia & Electrophysiology Review 2020; epub ahead of press. DOI http://sci-hub.tw/10.15420/aer.2020.20 Open access This work is open access under the CC-BY-NC 4.0 License which allows users to copy, redistribute and make derivative works for non-commercial purposes, provided the original work is cited correctly. The term narrow QRS tachycardia indicates individuals with a QRS duration ≤120 ms, while wide QRS tachycardia refers to tachycardia with a QRS duration >120 ms.1 Narrow QRS complexes are due to rapid activation of the ventricles via the His–Purkinje system, suggesting that the origin of the arrhythmia is above or within the His bundle. However, early activation of the His bundle can also occur in high septal ventricular tachycardia (VT), resulting in relatively narrow QRS complexes of 110–140 ms.2 Wide QRS tachycardias can be VT, supraventricular tachycardia (SVT) conducting with bundle branch block (BBB) aberration, or over an accessory pathway, and account for 80%, 15% and 5% of cases, respectively.3 The correct diagnosis of VT is critical to management, as misdiagnosis and the administration of drugs usually utilised for SVT can be harmful for patients in VT.4 In this article, we discuss the differential diagnostic methods encountered in clinical practice. The text is mainly based on the recently published ESC guidelines on SVT.1 Regular Tachycardias As a rule, the default diagnosis of a wide QRS tachycardia should be VT until proven otherwise. VT is defined as a tachycardia (rate >100 BPM) with three or more consecutive beats that originate in the ventricles.5,6 Differential diagnoses include (Table 1):7 SVT with BBB. This may arise due to pre-existing BBB or the development of aberrancy during tachycardia, known as phase 3 block, which more commonly has a right bundle branch block (RBBB) pattern due to the longer refractory period of the right bundle branch. SVT with antegrade conduction over an AP that participates in the circuit (antidromic atrioventricular re-entrant tachycardia) or is a bystander during AF, focal atrial tachycardia/flutter or atrioventricular nodal re-entrant tachycardia. SVT with widening of the QRS interval induced by drugs or electrolyte disturbances. Class IC and IA drugs cause use-dependent slowing of conduction and class III drugs prolong refractoriness to a greater extent at the His–Purkinje tissue than in the ventricular myocardium. Both can result in atypical BBB morphologies during SVT that mimic VT. Apical ventricular pacing, pacemaker-related endless loop tachycardia and artefacts can also mimic VT. Electrocardiographic Differential Diagnosis If the QRS morphology is identical during sinus rhythm and tachycardia, then VT is unlikely. However, bundle branch re-entrant VTs and high septal VTs exiting close to the conduction system can have similar morphologies to sinus rhythm. The presence of a contralateral BBB pattern in sinus rhythm is more indicative of VT. Atrioventricular Dissociation The presence of either atrioventricular dissociation or capture/fusion beats in the 12-lead ECG during tachycardia are key diagnostic features of VT (Table 2). Atrioventricular dissociation may be difficult to recognise because P waves are often hidden by wide QRS and T waves during a wide QRS tachycardia. P waves are usually more prominent in inferior leads and modified chest lead placement (Lewis lead).3 The relation between atrial and ventricular events is 1:1 or greater, i.e. more atrial than ventricular beats, in most SVTs. Atrioventricular nodal re-entrant tachycardia can be associated with 2:1 conduction, but this is rare.8 Although VA conduction can be found in up to 50% of patients with VT and a 1:1 relation is possible, most VTs have a relation of <1:1, i.e. more QRS complexes than P waves. QRS Duration A QRS duration >140 ms with RBBB or >160 ms with left bundle branch block (LBBB) pattern suggests VT. These criteria are not helpful for differentiating VT from SVT in specific settings, such as pre-excited SVT or when class IC or class IA antiarrhythmic drugs are administered.9
