In cases of tachycardia with a broad QRS complex, it is important to differentiate between supraventricular tachycardia (SVT) and ventricular tachycardia (VT). Electrocardiogram (ECG)-based differential diagnoses include VT vs. SVT with aberrant conduction, pre-existing bundle branch block (BBB), intraventricular conduction disturbances, and pre-excitation. Several criteria have been described for differentiation between VT and SVT in the presence of a wide QRS complex.
We report a case of wide QRS complex tachycardia with right BBB (RBBB) morphology and a retrograde P wave on the surface EC: SVT with antegrade conduction over an Accessory pathway, ‘pre-excited SVT’, which participates in the circuit (antidromic AVRT). Antidromic AVRT occurs in 3 - 8% of patients with WPW syndrome. Antidromic AVRT has the following ECG features illustrated in Figure 1 : A wide QRS complex (fully pre-excited) and an RP interval that is difficult to assess as the retrograde P wave is usually inscribed within the ST-T segment.
Most algorithms seeking to discriminate the two entities focus on identifying characteristics unique to VTs – that is to say, those with high specificity for VT – and presume all else to be SVT until proven otherwise.
Brugada’s stepwise approach for the diagnosis of VT was only modestly effective (sensitivity 80.6%; specificity 30.8%; The Vereckei algorithm showed better differential diagnostic accuracy (sensitivity 91.7%; specificity 61.5%; PPV 81.5%; NPV 80.0%). Diagnosis of wide QRS complex tachycardia with a RBBB pattern and a reversed R/S ratio in lead V6 usually favors VT; In Lead V1: Monophasic R, Rsr’, biphasic qR complex, broad R (>40 ms), and a double-peaked R wave with the left peak taller than the right (the so-called ‘rabbit ear’ sign are also favors VT.
In our case, the patient had a successful ablation of a left posterior accessory pathway.
In conclusion, wide complex tachycardia often exhibits an indistinct morphology, especially at higher frequencies, making diagnosis difficult. Despite all available morphological criteria, wide complex tachycardias are still misdiagnosed or can remain undiagnosed. To achieve a high positive predictive value of >95% in the identification of SVT, a systemic approach that employs a combination of various ECG and clinical criteria is needed.
Illustrations: picture (joint attached)