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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 compared with the outflow tract.


METHODS
A stepwise randomized cross-over protocol of programmed ventricular stimulation with alternating stimulation at both sites was used in 66 patients who were studied because of sustained ventricular tachycardia (n = 30), ventricular fibrillation (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 presence or absence of structural heart disease, spontaneous arrhythmia, ejection fraction or effective refractory periods. Overall, monomorphic 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 ventricular tachycardias have the same morphologies and similar (+/- 50 ms) cycle lengths. Ventricular fibrillation was inducible in 11 patients (17%), mostly by three extrastimuli (n = 8; 73%).


CONCLUSIONS
(1) stimulation from at least two right ventricular sites is desirable because of their independent contribution to the induction of ventricular tachyarrhythmias, (2) the non-inducibility or inducibility at one ventricular site does not predict the effect at another stimulation site, (3) the effective refractory period at the right ventricular apex and outflow 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 leads to ensure the correct interpretation of arrhythmias induced by programmed stimulation, (5) clinical or haemodynamic features cannot predict whether one or more stimulation sites will be required for induction of ventricular tachycardia. These results are important for the diagnostic evaluation and assessment of pharmacological or non-pharmacological interventions.