Differential diagnosis of wide QRS tachycardia under scrutiny

6 October 2008

MedWire News: The standard approach to the differential diagnosis of wide QRS tachycardia in patients with fixed bundle branch block (BBB) is flawed and may cause some patients to be wrongly diagnosed with ventricular tachycardia, say researchers.

The claim is made by Spanish cardiologists based on a prospective study of patients with fixed BBB and reported in the European Heart Journal.

It is widely held that the differentiation of wide QRS tachycardia in patients with preexisting wide QRS complex is simple: If the QRS complexes during tachycardia are identical to those in sinus rhythm, the tachycardia is supraventricular tachycardia (SVT); if they are different, the arrhythmia is ventricular in origin.

“This concept may be too simplistic and has not been tested in a systematic way,” write Tomás Datino (Hospital General Universitario, Madrid) and co-authors.

For this study, Datino et al analyzed QRS morphology during incremental rapid atrial pacing in 59 patients in sinus rhythm and QRS =120 ms but no pre-excitation.

On pacing, minor QRS changes were seen in 37% of subjects and major changes in 39%, the researchers report. One patient showed major axis shifts and none showed a change to the contralateral BBB pattern.

QRS changes were significantly and independently related to pacing rate and BBB type, being more frequent in those with right BBB. Furthermore, of 14 subjects with SVT, 13 displayed the same QRS changes during pacing.

Based on their observations Datino et al conclude: “If the 12-lead ECG morphology of a wide QRS tachycardia is different to that during sinus rhythm, but with the same BBB pattern, it does not necessarily imply that the tachycardia is ventricular.”

In an accompanying editorial, Hein Wellens (Cardiovascular Research Institute Maastricht, The Netherlands) remarked: “To make the correct diagnosis in a wide QRS tachycardia remains a challenge.

“In patients with the same type of BBB during sinus rhythm and tachycardia, there may be differences in QRS configuration without implying that the tachycardia is ventricular.”

Eur Heart J 2008; 29: 2351–2358