Augmentation of QRS wave amplitudes in the precordial leads during narrow QRS tachycardia

Introduction: QRS morphology during narrow QRS supraventricular tachycardia in patients without ventricular preexcitation generally is considered the same as that seen during sinus rhythm. This study presents a new ECG observ ation that the QRS amplitude increased significantly in leads V-2 through V -5 during tachycardia. Methods and Results: Using the same ECG machine and the same electrode patc hes applied to the same electrode positions, 12-lead ECGs during sinus rhyt hm and narrow QRS tachycardia were analyzed comparatively in 23 patients wi thout ventricular preexcitation, Precordial QRS amplitudes were measured as the vertical distance from the peak of the R to the nadir of the S wave. T he amplitudes also were measured during atrial rapid pacing and extrastimul ation, Furthermore, ventricular excitation during sinus rhythm and tachycar dia was studied using body surface mapping. Body surface distributions of Q RS potentials and ventricular activation time (VAT) were displayed as maps. Gross area of QRS (AQRS, equivalent to the QRS amplitude) was compared dur ing sinus rhythm versus tachycardia, During tachycardia, QRS amplitude sign ificantly increased in leads V-2 through V-5, without any noticeable change in the transitional zone or QRS wave duration. Increase of QRS amplitude a lso was noted during atrial rapid pacing and extrastimulation, Gross AQRS v alues during tachycardia significantly increased in the left parasternal ar ea, whereas QRS isopotential and VAT isochronal maps were similar during si nus rhythm and tachycardia, suggesting a minimal role of conduction delay i n the increase of QRS amplitude. Conclusion: QRS wave amplitude significantly increased in leads V-2 through V-5 during narrow QRS tachycardia compared with QRS waves in sinus rhythm. Increase of QRS amplitude seemed unlikely due to a conduction delay within the ventricular myocardium.