Characteristics of ischemic and peri-ischemic regions during ventricular fibrillation in the canine heart

Ischemic Ventricular Fibrillation. Introduction: Although premature beats o riginating in areas of ischemia have been shown to be important in initiati ng ventricular fibrillation (VF), the participation of the ischemic zone in maintenance of VF has not been investigated. Methods and Results: Ten normal dogs underwent induction of two separate ep isodes of VF, before and 10 minutes after left anterior descending coronary artery ligation, Ischemic VF was allowed to occur spontaneously or was ind uced by burst pacing after 10 minutes of ischemia. Unipolar epicardial elec trograms were recorded using an 8 x 14 plaque electrode array (interelectro de distance 2.5 mm) placed over the anterior wall. Activation during VF was characterized by VF cycle length (CL) and wavefront organization based on linking analysis of epicardial activation directions at adjacent sites. Ind ividual plaque sites were separated into regions based on electrogram morph ology during ischemia: R1 = no ischemia; R2 = mild-to-moderate ischemia (mi nor ST elevation and QRS widening); and R3 = severe ischemia (marked ST ele vation and QRS widening), Percent conduction block was calculated based on the percent of cycles during which sites were not activated during VF, Ther e were no significant differences noted in mean CL or mean percent conducti on block in the peri-ischemic region R1 compared to the same region under n onischemic (control) conditions. During ischemia, the mean CL was noted to increase in R2 from 111 +/- 14 msec (control) to 128 +/- 29 msec (ischemia) and in R3 from 113 +/- 14 msec (control) to 150 +/- 42 msec (ischemia) (P < 0.05). The percentage conduction block in R2 increased from 6% +/- 11% (c ontrol) to 14% +/- 16% (ischemia) and in R3 from 4% +/- 6% (control) to 44% +/- 21% (ischemia) (P < 0.05). Linking analysis revealed no significant ch anges in VF organization at distances of 2.5 mm in regions R1 and R2 under both control and ischemic conditions. Premature beats initiating fibrillati on originated at the border between the normal and mildly ischemic zones. Conclusions: (1) Some VF characteristics are altered in ischemic regions in cluding a longer VFCL and greater percentage of functional block, (2) VF ch aracteristics are unchanged in immediately adjacent nonischemic myocardium. (3) Although the ischemic zone may be involved in the initiation of VF and has unique activation characteristics during VF, it does not affect VF cha racteristics in the adjacent nonischemic zone, suggesting that it may not p lay a major role in VF maintenance.