Induction of electrical heterogeneity impairs ventricular defibrillation -An effect specific to regional conduction velocity slowing

Background-This study determined whether dispersion of conduction velocity, refractoriness, or excitability increases biphasic shock defibrillation en ergy requirements (DERs). Methods and Results-Twenty-four swine were instrumented with a mid-LAD perf usion catheter for regional infusion of lidocaine 0.75 mg.kg(-1).h(-1) (n= 7), low-dose d-sotalol (0.16 mg.kg-1.h-1) (n=4), high-dose d-sotalol (0.5 m g.kg(-1).h(-1)) (n=6). or saline (n=7). Effective refractory periods (ERPs) were determined at 5 myocardial sites, and regional conduction velocity wa s determined in LAD-perfused and -nonperfused regions. Regional lidocaine i nfusion increased DER values by 84% (P=0.008) and slowed conduction velocit y by 23% to 35% (P<0.01) but did not affect ERP. Conversely, regional low- and high-dose d-sotalol infusion did not alter DER values or conduction vel ocity but increased regional ERP by 14% to 17% (P<0.001), Regional lidocain e increased conduction velocity dispersion by 100% to 200% (P=0.01) but did not change ERP dispersion, whereas ci-sotalol increased ERP dispersion by 140% (P<0.001) without affecting conduction velocity dispersion. Lidocaine infusion induced ventricular fibrillation (VF) in 6 of 7 animals, whereas r egional d-sotalol was not proarrhythmic. Regional infusion of lidocaine and d-sotalol prolonged VF cycle length by 23% to 41% (P<0.05) in the perfused region and increased VF cycle length dispersion by 85% to 240% (P<0.05). B oth agents increased pacing threshold (excitability) in the perfused region by 93% to 116% (P<0.05). Conclusions-Regional conduction velocity slowing increased DER values, whic h was probably a result of spatial dispersion of conduction velocity. Incre asing refractory period dispersion without changing conduction velocity did not alter DFT values. Thus, dispersion of conduction velocity may be a mor e likely regulator of defibrillation efficacy than dispersion of refractori ness.