Time course of fibrillation and defibrillation thresholds after an intravenous bolus of amiodarone--an experimental study.
Experimental studies have described an increase in ventricular fibrillation threshold (VFT) by intravenous amiodarone. The aim of this study was to examine the early time course of changes in VFT and defibrillation thresholds (DFT) after an intravenous bolus of amiodarone in an experimental pig model of transient myocardial ischemia.


RESULTS
VFT and relative effective ventricular refractory period (ERP) were measured in 15 anaesthetized open-chest pigs after 3 min of regional coronary ischaemia before (time 0) and 2, 15, 30, 60, and 90 min after the intravenous injection of normal saline (group A, n = 5) or amiodarone, 5 mg/kg over 15 s (group B, n = 10). DFT was measured by increasing the strength of DC shocks until defibrillation was accomplished. Amiodarone caused an increase in VFT, starting at 2 min after the infusion (11.4 +/- 8.4 mA versus 9.2 +/- 4.6 mA, P = 0.03), became significant at 15 min (13.7 +/- 6.5 mA, P = 0.009), continued to rise at 30 min (34.2 +/- 28.7 mA, P = 0.03) and reached a plateau at 60 min (50.3 +/- 37.8 mA, P = 0.008). An increase was also observed in the ERP (204 +/- 25 ms at 2 min versus 197 +/- 26 ms at baseline, P = 0.074, 211 +/- 38 ms at 15 min, P = 0.084, 212 +/- 40 ms at 30 min, P = 0.037, 220 +/- 34 ms at 60 min, P = 0.002, and 227 +/- 32 ms at 90 min, P = 0.008). No change was observed in DFT after amiodarone administration. No significant change in VFT, ERP, or DFT occurred in the control group.


CONCLUSIONS
In this porcine model, the intravenous administration of amiodarone increased VFT and ERP over 60 min after the injection, without effect on DFT.
Tsagalou
Eleftheria P
EP
Department of Clinical Therapeutics, University of Athens School of Medicine, Alexandra Hospital, Makedonias 24, 104 33 Athens, Greece.
Anastasiou-Nana
Maria I
MI
Charitos
Christos E
CE
Siafakas
Costantinos X
CX
Drakos
Stavros G
SG
Ntalianis
Argirios
A
Terrovitis
John V
JV
Mavrikakis
Emmanuel M
EM
Doufas
Antonios
A
Nanas
John N
JN
D000638:Amiodarone / Q000008:administration & dosage*; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000008:administration & dosage*; D001794:Blood Pressure; D004056:Differential Threshold; D004554:Electric Countershock; D007275:Injections, Intravenous; D017202:Myocardial Ischemia / Q000150:complications*; D013552:Swine; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000209:etiology* / Q000503:physiopathology / Q000628:therapy*; D016277:Ventricular Function, Left / Q000187:drug effects
D000889:Anti-Arrhythmia Agents; D000638:Amiodarone