| Physiologic pacing can maintain normal hemodynamics and improves health-related quality of life. Results of recent trials suggest that in patients, interventricular synchronization is more important than atrioventricular synchronization. Interventricular synchronization acquired pacing in unconventional position and multiple position is more similar to physiological pacing. This animal experiment, under the conditions of dogs'exposed epicardial thoracotomy, is to study the different positions of ventricular pacing. Through researching the effects of different pacing modes on QRS duration (QRSd) and hemodynamics, the purpose is to reveal the relation of different ventricular pacing sites and cardiac electrophysiology and hemodynamics, hence to find out the physiological pacing or at least its resemblance.Objective To study the effects of five ventricular pacing modes in dogs on QRS duration (QRSd) and hemodynamicsMethods The experimental animals are twenty chosen healthy adult dogs, anesthetized with 3% napental (30mg/kg) in vein. After thoracotomy, the heart is exposed and ventilated by breathing machine. Seam electrode wire respectively on right ventricular apex (RVA) and the ventricular posterior lateral (LVPL) epicardial. Use tailor-made fine positioning pacing electrode to pass through right ventricular anterior wall to the endocardium of outflow tract (RVOT), and then determine pacing site.Separate femoral vein, insert artery sheathing canal, and then insert 7FSwan-Ganz floating catheter in this sheathing canal. Choose VDD mode of dual chamber pacemaker and test pacing threshold of different pacing site, with the pacing frequency of every pacing mode being 150 times per minute, which can capture sinus rhythm. The pacing modes employed in the test include right ventricular apical (RVA), right ventricular outflow tract (RVOT), right ventricular bifocal (right ventricular apex + right ventricular outflow tract ,RV-Bi), biventricular (right ventricular apex + left ventricular posterior lateral wall, Bi-V), and left ventricular (LVPL) pacing. The results are to be measured after 15 minutes when the pacing becomes stable, including QRSd, mean pulmonary artery pressure (mPAP), pulmonary capillary wedge pressure (PCWP), cardiac outflow (CO) and cardiac index (CI ). The parameter will be measured 3 times continuously with an average being chosen later. At the same time, QRSd is to be measured on electrocardiogram with a paper speed being 100mm/S or 200mm/S. Interval among different pacing modes is above 30 minutes, at this time, the rhythm being sinus rhythm.Results (1) RVOT pacing: compared with RVA pacing, displays a decrease in QRSd and an increase in the CO and CI(P<0.05), but the difference of mPAP and PCWP is not evident; compared with RV-Bi and Bi-V pacing, there is an increase in QRSd, mPAP and PCWP and a decrease in CO and CI(P<0.05). (2) RV-Bi and Bi-V pacing: compared with the right ventricular single pacing mode (RVA and RVOT pacing), shows a decline in QRSd, mPAP and PCWP while there is an increase in the CO and CI( P<0.05).There is no statistical significant difference between RV-Bi and Bi-V pacing. (3) Left ventricular pacing: compared with RVA pacing, shows a decrease in QRSd though with little difference; compared with RVOT, RV-Bi and Bi-V pacing, shows a increase in QRSd(P<0.05); compared with RVA and RVOT pacing, has a decrease in mPAP and PCWP but an increase in CO and CI(P<0.05); compared with RV-Bi and Bi-V pacing, however, displays no statistical difference in the hemodynamic parameters.Conclusion (1)The synchronism of ventricular contraction, an important factor that affects pacing hemodynamics, is influenced by QRSd. QRSd is the ventricle eliminates time, did not reflect that the ventricle concrete eliminates extremely the process, therefore the ventricle contracts the synchronism and QRSd the two also have not the relevant factor,, and the improvement for cardiac mechanical activity does not require cardiac electrophysiology synchronization. (2) There are synchronal improvements of cardiac electrophysiology and mechanical activities in ventricular both sites pacing modes (RV-Bi and Bi-V pacing), which displays excellent effects of cardiac electrophysiology and hemodynamics. (3) The ventricular single pacing mode (RVA, RVOT and LVPLpacing): the effects of cardiac electrophysiology and haemodynamics in right ventricular single pacing (RVA and RVOT pacing) are not as good as those of ventricular both sites pacing; the improved effects of cardiac electrophysiology in LVPLpacing is not obvious although, but it has effects similar to hemodynamics in ventricular both sites pacing and is is superior to the right ventricular single site pacing. |
