Lidocaine's effect on defibrillation threshold are dependent on the defibrillation electrode system: epicardial versus endocardial

Sedation in cardiac arrhythmias management

INTRODUCTION

Procedural sedation is of paramount importance for a plethora of electrophysiological procedures. From electrical cardioversion to electrophysiology studies, device implantations, and catheter ablations, intraprocedural sedation and anesthesia have a pivotal role in allowing procedural success while ensuring patient safety and avoiding discomfort. Areas covered: The present review will discuss the current state-of-the-art in sedation and anesthesia during electrical cardioversion, cardiac implantable electronic device implantation, catheter ablation and electrophysiology studies. Specific information will be provided for each procedure in order to reach the core of this important clinical issue, and specific protocols will be compared. The main pro-arrhythmic and anti-arrhythmic effects of the most commonly used sedatives will also be discussed. Expert commentary: According to much recent evidence, the cardiologist can be the only person responsible for sedation administration in many settings, highlighting few safety issues associated with the absence of a dedicated anesthesiologist thus a concomitant reduction in costs. However, many concerns have been raised in allowing non-anesthesiologists to manage sedatives, as adverse events, while rare, could have catastrophic consequences. The present paper will highlight when a cardiologist-directed sedation is considered safe, how it should be performed, and the pros and cons related to this strategy.

Regional gap junction inhibition increases defibrillation thresholds

It is clear that ischemia inhibits successful defibrillation by altering regional electro-physiology. However, the exact mechanisms are unclear. This study investigated whether regional gap junction inhibition increases biphasic shock defibrillation thresholds (DFT). Sixteen swine were instrumented with a mid-left anterior descending (LAD) perfusion catheter for regional infusion of 0.5 mM/h heptanol (n = 8) or saline (n = 8). DFT values and effective refractory periods (ERP) at five myocardial sites were determined. Regional conduction velocity (CV) was determined in an LAD drug-perfused and nondrug-perfused region in an additional seven swine. Regional heptanol infusion increased 50% DFT values by 33% (P = 0.01) and slowed CV by 42-59% (P < 0.01) but did not affect ERP. Regional heptanol also increased CV dispersion by approximately 270% (P < 0.05) but did not change ERP dispersion. Regional placebo did not alter any of these parameters. Furthermore, regional heptanol infusion induced spontaneous ventricular fibrillation in eight of eight animals. Increasing spatial conduction velocity dispersion by impairing regional gap junction conductance increased DFT values. Dispersion in conduction velocity slowing during regional ischemia may be an important determinant of defibrillation efficacy.

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 energy requirements (DERs).

METHODS AND RESULTS

Twenty-four swine were instrumented with a mid-LAD perfusion 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 mg. kg(-1). h(-1)) (n=6), or saline (n=7). Effective refractory periods (ERPs) were determined at 5 myocardial sites, and regional conduction velocity was determined in LAD-perfused and -nonperfused regions. Regional lidocaine infusion increased DER values by 84% (P=0.008) and slowed conduction velocity 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 velocity but increased regional ERP by 14% to 17% (P<0.001). Regional lidocaine increased conduction velocity dispersion by 100% to 200% (P=0.01) but did not change ERP dispersion, whereas d-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 regional 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). Both agents increased pacing threshold (excitability) in the perfused region by 93% to 116% (P<0.05).

CONCLUSIONS

Regional conduction velocity slowing increased DER values, which was probably a result of spatial dispersion of conduction velocity. Increasing refractory period dispersion without changing conduction velocity did not alter DFT values. Thus, dispersion of conduction velocity may be a more likely regulator of defibrillation efficacy than dispersion of refractoriness.