Management of postinfarct ventricular tachycardias

Comparison of conventional and biventricular antitachycardia pacing in a geometrically realistic model of the rabbit ventricle

INTRODUCTION

ICDs often are programmed with antitachycardia pacing (ATP) as the first response to ventricular tachycardia (VT). Many ICDs have an additional lead available for ventricular pacing. We hypothesized that using the additional lead for ATP would improve therapy by advancing the orthodromic wavefront, thereby reducing the size of the excitable gap and inducing block of all reentrant activity.

METHODS AND RESULTS

Monomorphic VT was initiated in a thin-walled model of rabbit ventricular myocardium that included an apical infarct and anatomically realistic dimensions. ATP with up to eight pulses was delivered at 90% of VT cycle length to one (conventional) or two (biventricular) stimulation areas. Stimulation areas were adjusted from 0.017 cm2 to 0.169 cm2 to modulate interactions between the antidromic and VT wavefronts, and between the orthodromic wavefront and the VT's refractory region. During conventional ATP, we found that larger stimulation areas terminated the VT in three pulses. Continued pacing after termination caused VT reinitiation in the reversed direction in some instances. With smaller stimulation areas, conventional ATP simply reset the circuit. During biventricular ATP, larger stimulation areas terminated VT in one pulse. There were no instances of reinitiation with reversal. However, with smaller stimulation areas, prolongation of refractoriness near the additional stimulation area facilitated induction of functional reentry with pathways modified by continued pacing.

CONCLUSION

Our modeling suggests that biventricular ATP is superior to conventional ATP under conditions where the additional ventricular lead effectively advances the orthodromic wavefront. Failure to achieve this advancement poses a risk of VT acceleration.

Utility of stress myocardial perfusion imaging performed before electrophysiologic testing

BACKGROUND

Patients considered for electrophysiologic study (EPS) are often first referred for stress myocardial perfusion scintigraphy (MPS) to assess for inducible ischemia before testing. The purpose of this investigation was to determine the utility of this approach by examining the relationship between MPS and any interim cardiac catheterization and revascularization, as well as the results and safety of EPS.

METHODS AND RESULTS

All patients undergoing EPS within 30 days after MPS at our institution between January 1997 and June 2000 were studied. Two hundred fifty-one patients met the inclusion criteria. The incidence of inducible sustained monomorphic ventricular tachycardia at EPS (IND) was 16%. One hundred twenty-nine patients had MPS ischemia (83 with high-risk features), but only twelve patients in all underwent revascularization between MPS and EPS. There were no ischemic complications during EPS. The presence of isolated ischemia on MPS was associated with a low rate of IND, not different from normal MPS findings (2%-3%). The combination of infarct and ischemia on MPS was associated with a high rate of IND that was similar to infarct alone (34% and 50%, respectively; P =.28).

CONCLUSIONS

Patients with high-risk MPS results are more likely to undergo revascularization before EPS than patients with low-risk or normal MPS results. However, most patients with high-risk MPS results undergo EPS without interim revascularization, and no patient had an ischemia-related complication at EPS. Larger studies will be required to confirm this observation. MPS infarct, not ischemia, is associated with IND at EPS.