Experimental Study Of Tachycardiomyopathy Produced By Rapid Right Atrial Pacing In The Pig

Objective: To establish a experimental model of tachycardiomyopathy by rapid rightatrial pacing at 240 beats per minute in pigs. Following, to evaluate the effects of bothshort-term (1 week) and prolonged (4 weeks) rapid atrial pacing on cardiac function,hemodynamics and myocardial remodling.Methods: Fifteen Diannan pigs were equally divided into five blocks by randomizedblock design according to sex, weight and age. Each block were randomly receivedthree managements: (1) rapid atrial pacing (240 beats/min) for 1 week(RAP_1w, n=5) ; (2) rapid atrial pacing (240 beats/min) for 4 weeks(RAP4_4w, n=5) ; (3) sham-operatedcontrols(CTL, n=5) . The control group received atrial pacemaker lead placement,followed by deactivation of the pacemaker. Clinical symptoms and hemodynamicparameters were used to evaluate the severity of tachycardiomyopathy.Echocardiographic study and left heart catheterization were performed to evaluate theeffects of both short-term(1 week) and prolong(4 weeks) rapid atrial pacing on cardiachemodynamics and cardiac function. Furthermore, we observed the differences ofmyocardial remodling between atrial and ventricular by light microscopic examinationand naked eye.Results: As pacing prolonged, the pigs developed congestive heart failure as evidencedby dyspnea, ascites and peripheral edema within 4 weeks of activating the pacemaker.Short-term tachypacing resulted in a significantly depressed ejection fraction (EF).Maximum rate of pressure development ( + dP/dt _Max) and maximum negative rate ofpressure development (-dP/dt _Max) were decreased lightly compared with CTL ( P<0．01) . Prolonged tachypacing caused biventricular cardiac dilation assessed byechocardiography, but no change in LV mass (P<0．05) . Compared with CTL, all indexsof systolic function became deteriorative after 4 weeks tachypacing ( all P<0．01) , andall indexs of diastolic function abnormal (all P<0．01) . Postmortom examinationrevealed a reduction in biventricular wall thickness compared with CTL after 4 weeks tachypacing ( all P<0．01) . Furthermore, light microscopy revealed the myocardialremodling with tissue fíbrosis being much more intense in left atrial tissue and fibrosisoccurred along the subendocardial layer after 4 weeks pacing.Conclusions: We can establish a experimental model of tachycardiomyopathysuccessfully by rapid right atrial pacing in the pigs which characterize with biventricularpump dysfunction, biventricular cardiac dilation, biventricular wall thickness and themyocardial remodling.