The retrograde His bundle deflection: its recognition and value in the analysis of tachyarrhythmias induced by stimulation on the T wave.

Interpretation of deflections presumably retrograde His bundle in origin has to be performed in context considering the coexisting changes in simultaneously recorded intracardiac and surface leads. His bundle electrocardiography thus conceived is helpful in the analysis of the runs of ectopic beats elicited by premature ventricular stimulation during the antecedent T wave in patients without coronary artery or primary myocardial disease. Identification of AV nodal echoes within the paroxysms as well as the subsequent runs of reciprocating tachycardias, was possible in patients with and without preexcitation, although a thorough study of these cases also requires recording of coronary sinus and low lateral right atrial electrograms. The behavior of the retrograde H deflection in respect to the first extra beat following the premature QRS complex helped in excluding bundle branch reentry. The latter is improbable in patients with 'complete' bundle branch block pattern, if extra beats show a contralateral bundle branch morphology. However, in absence of bundle branch block, retrograde H deflections were not helpful in elucidating the mechanisms of pacemaker-induced intraventricular (bundle branch, fasicular or vulnerability-related) reentry.