Effect of amiodarone on retrograde conduction and refractoriness of the His-Purkinje system in man

Editor's Choice-The treatment of electrical storm: an educational review

Electrical storm is characterised by a state of severe electrical instability that occurs in a rare combination of circumstances, and may lead to multiple implantable cardioverter defibrillator shocks and haemodynamic instability, and possible death. The main goal of treating electrical storm is to eliminate the trigger and modify the substrate of the arrhythmia. The aim of this educational review is to provide information for a better understanding of the underlying mechanisms and therefore help to improve the treatment of electrical storm patients.

Effects of cardioactive medications on retrograde conduction: Continuing relevance for current devices

INTRODUCTION

Retroconduction (ventriculo-atrial conduction) remains a problem for patients with implanted cardiac rhythm devices. Pacemaker algorithms can detect and terminate endless loop tachycardia (ELT), but actual prevention of ELT may require anti-arrhythmic drugs (AADs). Similarly, AADs can affect ICD rhythm discrimination algorithms that depend on atrio-ventricular ratios. There is concern whether these drugs remain effective during stress situations.

METHODS

Electrophysiologic studies that included retroconduction testing using slow ramp pacing were done in 1332 patients. The presence or absence of retroconduction at baseline and with drug was recorded, as was the rate at block. As a stress surrogate, isoproterenol was used to test retroconduction and reversal of drug-induced block.

RESULTS

Procainamide, mexiletine, phenytoin, disopyramide, quinidine, beta-blockers, encainide, and amiodarone caused complete retrograde block or decreased the rate at which block occurred (mean 76% of patients, p < 0.008), whereas digoxin, lidocaine, diltiazem, and verapamil did not. Isoproterenol (in the absence of AADs) increased the rate at block in 82% of 404 patients with retroconduction at baseline (p < 0.005). Of 319 patients without retroconduction at baseline, 134 (42%) developed retroconduction after isoproterenol. Isoproterenol reversed retrograde block in 39% of patients with block on an AAD. Amiodarone, digoxin, and the combination of digoxin plus a beta-blocker were most effective at resisting this reversal of ventriculo-atrial block (80%, 68%, and 75% respectively).

CONCLUSION

Most of the AADs reviewed increase the cycle length at block or abolish retroconduction, while isoproterenol has the opposite effect. Anti-arrhythmic medications, particularly amiodarone, digoxin, and the combination of digoxin plus a beta-blocker may be considered for a patient with multiple ELT episodes or certain ICD detection problems.

Amiodarone in the management of cardiac arrhythmias: current concepts

This article reviews current information on the clinical pharmacology, therapeutic utility, and adverse reactions of amiodarone, with emphasis on guidelines for its rational use.

Atenolol and amiodarone: a comparative study of their anti-ischaemic effect

A total of 10 patients with mixed angina were entered into a study to compare the anti-ischaemic efficacy of atenolol and amiodarone. The study was divided into three parts: (a) placebo for 2 weeks; (b) 100 mg atenolol given for 8 weeks; and (c) amiodarone given for 8 weeks, divided into week 1, 200 mg three times daily; week 2, 200 mg twice daily; weeks 3 and 4, 200 mg once daily; weeks 5-8, 200 mg once daily for 5 days a week. Clinical examination, basal and multi-stage effort electrocardiograms were performed at the end of each treatment. The number of anginal attacks and the amount of trinitrin taken by the patients were significantly reduced by both drugs with no significant difference between them. Compared with placebo, both drugs induced a significant increase in work capacity and in the time to decrease the ST-segment by 1 mm. At rest, atenolol reduced systolic blood pressure, heart rate and the systolic blood pressure--heart rate product compared with placebo. Systolic blood pressure was also reduced significantly compared with patients given amiodarone. Amiodarone did not influence these parameters. At maximum effort, amiodarone reduced heart rate and the systolic blood pressure--heart rate product compared with placebo. This reduction was greater for atenolol. The ST-segment depression was comparable between patients given either test drug. Amiodarone, therefore, exerts an anti-ischaemic effect similar to that shown by atenolol with different haemodynamics: atenolol reducing myocardial oxygen demand, amiodarone having an additive increase of coronary flow. Such an effect was obtained with a lower dose of amiodarone than is commonly used.

Kinetics of electrophysiologic changes during oral loading of amiodarone and after withdrawal of amiodarone in the unsedated dog

We examined the temporal kinetics of onset and offset of the cardiac electrophysiologic effects of orally administered amiodarone in chronically instrumented, unsedated adult dogs (n = 8). Right atrial (RA), atrioventricular nodal (AVN), and right ventricular (RV) effective refractory period (ERP), and AVN functional refractory period (FRP), were determined daily for 21 days during amiodarone loading (24 mg/kg/day) and for 21 days after cessation of amiodarone. Left ventricular (LV) ERP was assessed in four of eight animals. Group mean RA-ERP peaked and plateaued early during amiodarone loading (time to reach one-half observed peak change [t1/2 onset] = 1.2 +/- 0.5 days) and rapidly returned toward baseline after cessation of drug (decay time to one-half peak value [t1/2 offset] = 2.0 +/- 1.7 days). Group mean RV-ERP rose in a linear manner throughout the loading period (t1/2 onset = 9.3 +/- 2.1 days) and remained elevated after cessation of drug (t1/2 offset greater than 21.0 days). Group mean AVN-ERP and FRP exhibited temporal kinetics intermediate between those of the RA-ERP and RV-ERP, both during amiodarone loading and after cessation of the drug. Group mean LV-ERP onset kinetics (assessed in a limited number of animals, n = 4) appeared to differ from RV-ERP onset kinetics (t1/2 onset = 2.5 +/- 2.5 days), whereas LV-ERP and RV-ERP offset kinetics appeared similar (t1/2 offset greater than 21 days). In summary, our findings demonstrate that during oral loading, the temporal sequence of onset of amiodarone-induced electrophysiologic effects is site dependent. Similarly, after cessation of amiodarone, the persistence of drug-induced electrophysiologic effects is both variable and site dependent.