Wave Length Restitution Changes In Ventricle Affecting The Initiation Of Ventricular Fibrillation During Acute Myocardial Ischemia

Objective Ventricular Fibrillation (VF), especially after acute myocardial ischemia, is the major cause of sudden cardiac death. The purpose of this study based on the hypothesis of Multiple-wavelet, using the theory of restitution properties, is that 1) during acute myocardial ischemia period, once the ventricular tachycardia(VT) occurs, it can induce the VF more easily; 2) the restitution of wave length (WL) affecting the initiation of ventricular fibrillation is more important than APD or CV restitution separately.MethodsFifteen adult canines weight during 13kg to 16kg anesthetized with 1mg/kg sodium pentobarbital, intubated, and ventilated with room air by a respirator. By surgical method, we open the canine chest to expose the heart. Then we position the 64-lead epicardial mapping plaque on the free wall of left ventricle, avoiding the coronary artery as far as possible. Then we deploy the bipolar stimulus catheter on the right side of the plaque. S₁S₂ stimuli outputted in 25mV is delivered to the normal and the acute ischemia ventricular myocardium. The baseline stimuli (S₁), which begins at 250ms, is gradually shortened by 10ms until ventricular fibrillation is induced. The premature stimuli begins at 150ms. We decrease its time until it cannot capture the ventricle. The longest S₁-S₂ interval associated with S₂ noncapture was the effective refractory period (ERP) for that S₁ cycle length (CL) of S₁. If ventricular fibrillation was induced, a 10J shock was delivered to the left and right ventricles for defibrillation. Construct the restitution curve of APD, CV and WL. Then we measure the slope steepness of APD, CV and WL restitution curve in the normal and acute ischemia ventricular myocardium. The changes and differences between the normal and the ischemia can be found.ResultsComparing the differences of slope steepness of APD, CV and WL between the normal and the acute ischemia, we found the slope steepness of WL restitution curve are both significant. We also gain the significance in the threshold of VF in the same comparison.DiscussWhen acute ischemia occurs within 1 to 2 hours, the value of PI inducing ventricular fibrillation is increased; the threshold of ventricular fibrillation is decreased. So once the ventricular tachycardia (VT) onsets, it can transform to ventricular fibrillation easily.The slope of APD or CV restitution curve cannot evaluate the threshold of VF independently. The product of APD and CV is wave length (WL) of excited wave. Instead, the restitution of WL can evaluate the threshold of VF. So during acute myocardium ischemia, VF can easily be induced when the slope of the curve of WL restitution becomes steep. Above all, WL restitution is a effective index to predict the possibility of VF onset.Conclusions1. During acute myocardial ischemia period, once the ventricular tachycardia (VT) onsets, it can induce the VF more easily;2. When acute ischemia occurs, the slope of wave length (WL) restitution curve is significantly steeper than APD or CV restitution curve, so WL restitution is better to predict the possibility of the transformation from VT to VF than APD restitution or CV restitution separately.