COMPARISON OF THE RESULTS OF PROGRAMMED VENTRICULAR STIMULATION FROM THE RIGHT-VENTRICULAR APEX AND OUTFLOW TRACT - A RANDOMIZED, PROSPECTIVE-STUDY

Objective: The aim of this prospective study was to analyse the yield of programmed ventricular stimulation at the right ventricular apex co mpared with the outflow tract. Methods: A stepwise randomized cross-ov er protocol of programmed ventricular stimulation with alternating sti mulation at both sites was used in 66 patients who were studied becaus e of sustained ventricular tachycardia (n=30), ventricular fibrillatio n (n=7), or non-sustained ventricular tachycardia and/or syncope (n=29 ). Results: There were no significant differences between the results of stimulation from either right ventricular site with regard to the p resence ol absence of structural heart disease, spontaneous arrhythmia , ejection fraction or effective refractory periods. Overall, monomorp hic ventricular tachycardia was inducible in 33 patients (50%), in 25 patients (75.8%), this arrhythmia was induced from both sites. However , in only 17 of these 25 patients (68%) did the induced monomorphic ve ntricular tachycardias have the same morphologies and similar (+/-50 m s) cycle lengths. Ventricular fibrillation was inducible in II patient s (17%), mostly by three extrastimuli (n=8; 73%). Conclusions: (1) sti mulation from at least two right ventricular sites is desirable becaus e of their independent contribution to the indiction of ventricular ta chyarrythmias, (2) the non-inducibility or inducibility at one ventric ular site does not predict the effect at another stimulation site, (3) the effective refractory period at the right ventricular apex and out flow tract do not differ; (4) the inducibility of multiple ventricular tachycardia morphologies emphasizes the importance of documenting the cause of spontaneous arrhythmias with multiple electrocardiographic l eads to ensure the correct interpretation of arrhythmias induced by pr ogrammed stimulation, (5) clinical or haemodynamic features es cannot predict whether one or more stimulation sites will be required for ind uction of ventricular tachycardia. These results are important for the diagnostic evaluation and assessment of pharmacological or non-pharma cological interventions.