The Study Of Effects Of Single-chamber And Dual-chamber Pacing On Cardiac Function

Objective: For losing atrioventricular synchrony, single-chamber pacing in RVA may lead to cardiac systolic and diastolic function decline. Studies have proved that the patients who had single-chamber pacing in RVA may have a higher incidence of atrial fibrillation or stroke. By restoring atrioventricular synchrony, dual-chamber pacing may bring better hemodynamic effects than single-chamber pacing in RVA. But there was no evidence-based information confirmed such benefits can enhance survival rate of patients in a long term.Brain natriuretic peptide is an inside natriuretic peptide in human body, ventricular myocardium could secrete this substance in response to blood volume and pressure increased. B-type natriuretic peptide (BNP) has the function of natriuretic, reducing pulmonary capillary pressure, inhibiting renin secretion and synthesis of aldosterone. N-terminal pro-B-type natriuretic peptide (Nt-proBNP) and BNP were released from ventricular myocytes together, but Nt-proBNP has no bioactivity. For Nt-proBNP has a long half-life in vivo, so the plasma concentration of Nt-proBNP is 1～10 times higher than BNP in patients who have chronic congestive heart failure. Compared with BNP, Nt-proBNP is more conducive for the diagnosis of heart failure.The aim of this study is to explore the effects of VVI/DDD modes on the cardiac function and its possible mechanism by comparing the differences of plasma Nt-proBNP levels and cardiac ultrasonography indexes of patients who accepted pacemaker implantations before and after implantation and also distinguished between two pacing modes.Methods: 51 patients (mean age 66.61±9.79 years, 25 male and 26 female) with sick sinus syndrome or atrioventricular block who accepted permanent pacemaker implantations in No.2 hospital of Hebei Medical University from May, 2006 to December, 2007 were enrolled, exclusion criteria include acute coronary syndrome,pulmonary heart disease,severe disfunction in liver and kidney,stroke,hyperthyroidism and electrolyte disturbance. All patients'cardiac function was over New York Heart Association (NYHA) classⅡ. Based on pacing modes, all patients were divided into two groups: VVI (n=38) and DDD (n=13) (Table1). On the basis of the cumulative percentage of ventricular pacing(Cum%), the patients selected VVI /DDD were divided into four subgroups: VVI(Cum %<50%),VVI(Cum %≥50%),DDD(Cum %<50%),DDD(Cum %≥50%).The patients were taken blood samples before and 7 days after the implantation, cardiac ultrasonography was performed before implantation and 3 months after implantation, and pacemaker programmed were taken to record cumulative percentage of ventricular pacing at 7 days after the implantation. The plasma Nt-proBNP levels,cardiac ultrasonography indexes of patients in different pacing modes were self-contrasted in each group before and after the implantation, also distinguished between two pacing modes.Measurement data were expressed as mean±standard deviation (SD), statistical analysis was performed by using SPSS 13.0. Independent-Samples T Test was performed to determine the differences between groups. P value<0.05 was required for statistical significant.Results:1 LVEF,SV showed a decreasing trend after implantation comparing with theirs before implantation in VVI group, and the difference approaching a significant statistical difference (P=0.07); CO decreased after implantation comparing with theirs before implantation in VVI (Cum%≥50%) group and there was significant statistical difference (5.86±1.56 L/min vs 4.05±0.94 L/min, P<0.05); LVEF,SV showed a decreasing trend after implantation in VVI (Cum%≥50%) group. LAD showed a decreasing trend and SV showed an increasing trend after implantation comparing with theirs before implantation in DDD group, and the differences approaching a statistical difference.2 SV was higher in VVI group than in DDD group before implantation, the difference has statistical significance (85.86±23.01ml vs 63.86±17.63ml,P<0.05). LVEF was lower in VVI group than in DDD group after implantation, the difference has statistical significance (63.37%±11.32% vs 73.29%±5.47%, P<0.05). LVEF was lower in VVI (Cum%≥50%) group than in VVI (Cum% < 50%) group after implantation, and the difference approaching a significant statistical difference (P=0.06).3 There were not significant differences on the plasma Nt-proBNP levels after implantation comparing with theirs before implantation in each group, there were not significant differences on the plasma Nt-proBNP levels after implantation comparing with theirs before implantation in each subgroup.4 There were not significant differences on the plasma Nt-proBNP levels before or after implantation between VVI group and DDD group, and there were not significant differences on the plasma Nt-proBNP levels before or after implantation between subgroups in each group.ConclusionRight ventricular apex pacing could damage left ventricular systolic function partly. The higher of cumulative percentage of ventricular pacing was, the more severe adverse hemodynamic effects may RVA pacing bring. Long term effects of right ventricular apex pacing on cardiac function are still required further clinical observation.