Idiopathic ventricular fibrillation

ECG11 A: Sinus rhythm, borderline PR-interval; ventricular extrasystole triggering a very rapid, irregular, polymorphous ventricular tachycardia, with spontaneous termination after about fifteen complexes; resumption of sinus rhythm; this short episode was responsible for a lightheadedness;

ECG 11B:

ECG 11B: Tracing recorded a few seconds after the first tracing; identical ventricular extrasystole (originating from the base of the left ventricle), sllghtly early, causing the rhythm to degenerate into a very rapid, irregular polymorphic tachycardia corresponding to a coarse ventricular fibrillation;

ECG 11C:

ECG 11C: End of the episode; the fibrillation resolves spontaneously after fifteen seconds;

Comments: Ventricular fibrillation constitutes of ventricular electrical activity that is completely disorganized, chaotic and unsynchronized, with disappearance of the alternation between systoles and electrical diastoles replaced by weak and rapid movements of the ventricular wall totally devoid of hemodynamic efficiency and leading to circulatory arrest. On the 12-lead electrocardiogram (rarely recorded in this setting given the life-threatening emergency), there is a completely irregular high rate succession of signals of varying duration and amplitude among which we can no longer recognize P waves, QRS complexes or T waves. This pattern of electrical tremor generally evolves over time (over a period of a few seconds to several minutes) with, in the absence of treatment, progression from a tracing with high amplitude oscillations to a tracing with low amplitude signals which precedes the flat agonic tracing. The onset of the ventricular fibrillation can be abrupt (ventricular fibrillation at the outset) triggered by a generally early ventricular extrasystole or occur after a more or less prolonged duration of monomorphic or polymorphic ventricular tachycardia. Ventricular fibrillation corresponds to multiple micro-reentry circuits that develop, propagate and interfere with one another at the centre of a sufficient critical myocardial mass. The triggering of this disorganized ventricular arrhythmia requires a pacing of the ventricular myocardium at the time of its vulnerable phase (most often one or more extrasystoles) and an inhomogeneity in terms of refractory periods and conduction velocities of the myocardial fibers. This rhythm is self-sustaining which explains its generally irreversible character and the occurrence of sudden death in the absence of electrical shock, the only therapy allowing the return of effective hemodynamics. It rarely causes syncope since the spontaneous termination are exceptional (except after several minutes allowing an asystole).

The particularity of the clinical picture of this patient resides in the fact that the episodes of ventricular fibrillation occur in the total absence of any identifiable context and that they terminate spontaneously causing a typical symptomatology of repeated syncopes. The term idiopathic fibrillation is used when it occurs in an anatomically healthy heart, in the absence of underlying cardiac disease diagnosed after comprehensive assessment, in the absence of any functional or structural abnormality, in the absence of arguments for various channelopathies (Brugada syndrome, long QT, etc.) or major temporary electrophysiological abnormalities (ischemia, metabolic or electrolyte disorders, drug side effect). It is therefore a diagnosis of exclusion. Idiopathic ventricular fibrillations account for less than 5% of all fibrillations and occur predominantly in certain young patients under 50 years of age. It is likely that in the future, with the development of advanced imaging and gene mapping techniques, an explanation can be found for all or some of the cases defined today as idiopathic. This patient underwent implantation of a defibrillator, given the potentially major risk of sudden death.

Take-home message: Ventricular fibrillation corresponds to a completely disorganized, chaotic and unsynchronized ventricular electric activity reflected on the ECG by a totally irregular high-rate succession of signals of variable duration and amplitude among which one can no longer recognize P waves, QRS complexes or T waves.