MAPPING OF SEPTAL VENTRICULAR-TACHYCARDIA - CLINICAL AND EXPERIMENTALCORRELATIONS

In patients with chronic myocardial infarction, ventricular tachycardi a originating in the interventricular septum may account for a signifi cant number of arrhythmia recurrences after direct ablative operations . We used total computer-assisted cardiac mapping (epicardial sock, le ft and right ventricular endocardial balloon electrode arrays) to asse ss whether tachycardia originating in deep or right-sided layers of th e interventricular septum is associated with a specific pattern of epi cardial activation sequence. We performed these studies during operati ons in 18 patients and during experiments in 12 dogs in which a septal myocardial infarction was produced by ligating the anterior septal, c oronary artery, Intraseptal needle electrodes were plunged into the se ptum of all animal preparations to generate pace-mapping data and to o btain intraseptal recordings (six preparations) during reentrant ventr icular tachycardia induced by programmed stimulation. In addition, pac e-mapping data of infarcted canine heart preparations were compared wi th those of nine healthy heart preparations, In the clinical study, 31 ventricular tachycardias with a septet site of origin were analyzed., Twenty tachycardias displayed an epicardial breakthrough in the area of the interventricular groove, whereas II had an epicardial breakthro ugh in the right ventricular free waif, Biventricular endocardial mapp ing revealed that left septal endocardial activation preceded right se ptal activation in the Former and that right septal activation occurre d earlier in the latter, In the experimental study, 14 ventricular tac hycardias (cycle length 146 +/- 31 msec) were induced by programmed st imulation in II infarcted heart preparations, Eight tachycardias displ aying an epicardial breakthrough on the right ventricle were found to originate in the right ventricular septal subendocardial layers, where as six tachycardias in which the epicardial breakthrough occurred on t he anterior interventricular groove originated in the left ventricular septal subendocardial layers. The epicardial breakthrough preceded th e left ventricular endocardial breakthrough in sir: tachycardias (85.7 %) originating in intermediate or right ventricular septal layers, but in only one of five tachycardias originating in the left ventricular septal layers, In the pace-mapping study, the epicardial: breakthrough shifted progressively from the right ventricular free wall toward the interventricular groove area in response to pacing from the right, in termediate, and left ventricular thirds of the basal septum, This rela tionship was similar for infarcted and noninfarcted hearts, although t ransseptal conduction time was prolonged in infarcted hearts (45 +/- 1 0 msec vs 33 +/- 7 msec, p < 0.01). Therefore the information integrat ed from the localization of the epicardial breakthrough and the relati ve timing between the epicardial and the left ventricular endocardial breakthroughs can be used to estimate the depth of the site of origin of septal ventricular tachycardias. This study confirms that a three-d imensional view of the substratum of ventricular tachycardia can be de rived from simultaneous epicardial and left ventricular endocardial ma pping and earn provide a superior basis for therapeutic interventions.