In 38 isolated bull-frog hearts, ventricular fibrillation was initiated by changing perfusion fluid from Ringer's solution to the low sodium and potassium solution; i.e. iso-osmotic solutions of glucose, fructose, sucrose, tris-hydroxymethylaminomethane, and so on. The ventricular fibrillation thus induced was easily reversible to sinus rhythm and highly reproducible as well, and it could be prevented by the presence of either sodium or potassium ion. During the event, the atrium continued to beat with regular sinus rhythm, except for one deteriorated case which developed atrial fibrillation. One of the precipitating factors was the hydrostatic pressure exerted onto the cardiac cavity.
ECG findings seen in these experiments were characterized by the following:
(1) Immediately after the perfusion medium was replaced, QRS complexes became wider and more bizarre from beat to beat, and QT interval shortened progressively, together with directional T wave change in Y lead, until ventricular fibrillation developed in 20 to 40 sec.
(2) The QRS complex of the first beat of ventricular fibrillation had a short coupling interval with a deflection in the same direction as those of the preceding sinus beats.
(3) The subsequent rapid ventricular rhythm was comparatively regular in its initial stage at the rate of 250 to 400 per min., getting more and more irregular in amplitude and frequency in the course of time.
The mechanisms involved in the production of the ventricular fibrillation have been discussed.
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