Pacing-Site Dependent Differences Of Myocardial Repolarization Time Of The Left Ventricular Wedge In Canine

PartⅠEvaluation of pacing site dependent difference of transmural myocardial repolarization time in a left ventricular wedge preparation model of normal canineObjective In addition to the cardiac resynchronization therapy, several pacing modalities have been used for the treatment of drug-refractory heart failure, such as multiple sites pacing from either right ventricular endocardium or left ventricular epicardium. They might have different impact on the electrophysiological properties of myocardium and lead to fatal ventricular arrhythmias. This study is to investigate the effects of different pacing site on the transmural dispersion of myocardialrepolarization time in a left ventricular wedge preparation model of normal canine.Methods We followed the protocols of our lab and those reported in previous publications. In brief, after the heart was excised from an anesthetized and anticoagulated dog,transmural wedges with dimensions of (2.0-4.0)cm*(1.0-2.0)cm*(1.0-1.5)cm were dissected from the free wall of the left ventricle. The tissue was cannulated via a native branch of left descending coronary artery and perfused with Tyrode's solution.Transmembrane action potentials from sub-epicardial, Mid-myocardial, and sub-endocardial sites were simultaneously recorded using floating glassmicroelectrodes. A transmural ECG calculated by subtracting the transmural activities from sub-epicardium through the sub-endocardium is recorded concurrently. Stimulations w delivered from single or dual sites of endocardium or epicardium, and simultaneously from both endocardium and epicardium. Parameters representing myocardial repolarization time and its transmural dispersion, such as QT interval, T wave peak-to-end interval (Tp-Te), and Tp-Te/QT, were measured and compared between different pacing strategies. Arrhythmias induced during the stimulation were also recorded.Results Our results showed that the Tp-Te interval was 83.63±19.30ms,75.63±16.47ms,54.75±13.18ms (P<0.01) and Tp-Te/QT was 0.280±0.049,0.266±0.042,0.201±0.0371 (P<0.01) when the stimulation was delivered from epicardium alone, endocardium and epicardium, or endocardium alone respectively,indicating that simultaneous pacing from endocardium and epicardium increased the transmural dispersion of myocardial repolarization and was associated more induced arrhythmias (75%,60% vs.13%, P=0.03). However, if the stimulations were delivered from dual sites of ipsilateral endocardium or epicardium, both Tp-Te andTp-Te/QT decreased comparing to those of single site pacing (P<0.01). Conclusion It is concluded that simultaneous pacing from endocardium and epicardium increased the transmural dispersion of repolarization and the risk of developing ventricular arrhythmias; which might be avoided by multiple sites pacing from ipsilateral of either endocardium or epicardium. These findings call for further studies focus on improving the pacing system and its implant techniques utilized in the heart failure patients. Part II Evaluation of pacing site dependent difference of transmural myocardial repolarization time in a left ventricular wedge preparation model of DCM-CHF canineAbstract:Objective According to the state of cardiac resynchronization therapy of heart failure in clinic, this study is to investigate the effects of different pacing site on the transmural dispersion of myocardialrepolarization time in a left ventricular wedge preparation model of DCM-CHF canine.Methods:A special pacemaker was implanted to either of 8 complete AVB canine.This device worked in a VOO model and the pacing rate was set to 240bpm. The dogs showed CHF symptoms,signs several days after the operation,and then LV enlargement appeared three weeks later. The left ventricular wedge preparation model was made.The same pacings were gived as PartⅠ, T wave peak-to-end interval (Tp-Te), and Tp-Te/QT, were measured and compared between different pacing strategies. Arrhythmias induced during the stimulation were also recorded.Results:The DCM-CHF models were successfully prepaired. Our results showed that the QRS interval, QT interval, Tp-Te/QT were longer (bigger) of DCM-CHF models than that of normal ones. The same time,pacing with LV-Epi resulted in TDR elongation was also exsist in DCM-CHF models,and was associated more induced arrhythmias(P<0.01). However, if the stimulations were delivered from dual sites of ipsilateral endocardium or epicardium, both Tp-Te and Tp-Te/QT decreased comparing to those of single site pacing (P<0.01).Conclusion:It means that both DCM-CHF itself and different pacing site contributed to the arrhythmias of this condition.It is concluded that CHF patients who were treated by心脏再同步化治疗had more risk factors developing ventricular arrhythmias; These findings call for further studies focus on improving the pacing system and its implant techniques utilized in the heart failure patients.