ENDOCARDIAL MAPPING OF VENTRICULAR-TACHYCARDIA IN THE INTACT HUMAN VENTRICLE .3. EVIDENCE OF MULTIUSE REENTRY WITH SPONTANEOUS AND INDUCED BLOCK IN PORTIONS OF REENTRANT PATH COMPLEX

Objectives. This study was conducted to characterize the functional na ture of the reentrant tract responsible for ventricular tachycardia du e to ischemic heart disease, Background. A zone of slow conduction for ming the return path is thought to form a critical component of the re entrant mechanism in ventricular tachycardia. Despite its importance, detailed knowledge of the return path is rare in clinical studies. Met hods. Multielectrode arrays were used intraoperatively to obtain unipo lar and high gain bipolar recordings of left ventricular endocardium i n patients undergoing map-directed surgical ablation of ventricular ta chycardia. A total of 224 local electrograms were analyzed for each ta chycardia. Results. Of 10 consecutive patients undergoing intraoperati ve cardiac mapping, detailed recordings of the return tracts of eight ventricular tachycardias were obtained in three patients. The recordin gs demonstrated that return tracts can be complex and extensive, with multiple paths of entry and exit. Potential and actual alternate paths were observed. Spontaneous and induced block occurred within portions of the complex. Intermittent block in one of two paths of entry resul ted in intermittent cycle length changes of the tachycardia without a change in configuration. Block in one exit path resulted in a shift to alternative exit paths, with dramatic changes in ventricular activati on and tachycardia configuration. Termination of the tachycardia could result from block close to the entrant or exit portion of the return tract. Different tachycardias were seen to share common portions of a return tract. Conclusions. These observations enlarge and extend our k nowledge of the functional repertoire of complex reentrant tracts that occur in infarct-related ventricular tachycardia. The use of common p ortions of a reentrant tract by several tachycardias is confirmed. Uti lization of alternate pathways can account for changes in configuratio n and cycle length. Spontaneous and induced block can occur at points of entry and exit in a reentrant tract and may identify optimal target s for ablation attempts. Further advances will require greater emphasi s on diastolic activation mapping.