Despite years of intense research into the mechanisms of defibrillation, th
ere remain many unanswered questions. In many fields, hypotheses are first
tested in rodent models before confirming the results in larger animals. Th
is work suggests the guinea pig as a rodent model for defibrillation. Twent
y-eight guinea pigs were studied, all male retired breeders weighing over 9
00 g. T-wave stimuli (upper limit of vulnerability [ULV]) were given after
15 rapid pacing beats, since the rapid pacing has been suggested to extend
the tachyarrhythmia. Defibrillation (DF) was attempted after 5 seconds. The
correlation between the ULV50 and DF50 in guinea pigs (0.82, n = 8) is ver
y close to that seen in dogs (0.85). Also, the sensitivity of the DF50 to w
aveform is similar (476 +/- 176 for monophasic vs 364 +/- 94 V for biphasic
P < 0.005, n = 10). The dose-response curve widths (2.3 +/- 1.7 for ULV vs
1.9 +/- 1.8 for defibrillation, n = 10) show the same trend of increasing
curve widths for ULV, and similar magnitude to dogs (mean 1.8). We rarely (
<1.5%) observed spontaneous conversion in less than 10 seconds. The guinea
pig can be used as a model for defibrillation as it shows many of the same
characteristics as dogs.