Calcium-dependent fluorescence transients during ventricular fibrillation.
Using surface fluorometry, calcium-dependent fluorescence transients were recorded during ventricular fibrillation in perfused rat and hamster hearts loaded with INDO 1-AM (fluorimetric reagent for calcium ion). Among a series of 203 consecutive isolated heart studies, 13 instances of ventricular fibrillation occurred. These arrhythmias developed during pretreatment with isoproterenol, dobutamine, norepinephrine, phenylephrine, digoxin, and 4 mmol/L calcium in the perfusate. Alternans behavior of calcium transients occurred in three cases; premature beats preceded ventricular fibrillation in six cases. Premature beats led to a further increase in the free intracellular calcium ([Ca2+]i) concentration, resulting in a stronger contraction with the subsequent beat and/or the initiation of ventricular fibrillation. Two distinct patterns of calcium transients were seen: ventricular fibrillation type 1 showed fast disorganized transients with small amplitude and an irregular, nonuniform tracing; type 2 revealed fast activity and multiform, polymorphous transients with marked changes in amplitude. Independent of the morphologic type of fibrillation, [Ca2+]i remained constant or even increased during an observation time up to 9 minutes. No intracellular hypocalcemia was observed. Isoproterenol pretreatment resulted in [Ca2+]i levels in the range of the end-diastolic calcium level of the last regular contraction. Fibrillating calcium transients after norepinephrine, dobutamine, phenylephrine, digoxin, high calcium, and fast pacing were in the previous end-systolic range. It is suggested that inotropic agents acting without a major elevation of cyclic adenosine monophosphate result in higher [Ca2+]i.
Stefenelli
T
T
Department of Medicine (Cardiology), University of California, San Francisco.
Wikman-Coffelt
J
J
Wu
S T
ST
Parmley
W W
WW
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D005453:Fluorescence; D005470:Fluorometry; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000378:metabolism / Q000503:physiopathology*
D002118:Calcium