The evaluation of the acute effect of ventricular activation sequence change induced by right ventricular apical pacing on the systolic and diastolic functions of the right and the left ventricle by echocardiography and radionuclide ventriculography.

Aim: The aim of this study was to evaluate the acute effect of ventricular activation sequence change induced by right ventricular apical pacing on the systolic and diastolic functions of the right and the left ventricle (LV) by echocardiography and radionuclide ventriculography (RNV) in patients without structural heart disease.Methods: Seventeen patients with dual chamber pacemakers implanted for sick sinus syndrome(SSS) were studied. All had intact atrioventricular (AV) nodal conduction and narrow intrinsic QRS complexes and an apically placed ventricular lead in the right ventricle. They were evaluated by echocardiography and RNV in two pacing modes; first in Mode 1: AAI with intrinsic AV conduction and 5 minutes later in Mode 2 (DDD with the longest possible AV interval that resulted in 100 % ventricular pacing). Left and right ventricular end-diastolic and end-systolic volumes, ejection fractions (EF), myocardial performance index, inter- and intraventricular dyssynchrony indexes were calculated in the two pacing modes.Findings: The left atrial diameter was larger in mode 2 as compared to mode 1 (37,1 ± 3,9 vs 35,5 ± 2,4; p=0,014). The LV end-diastolic volume was lower in mode 2 as compared to mode 1 both by echocardiography and RNV (96,3 ± 10,9 vs 110,8 ± 18,6; p=0,017, 94 ± 11 vs 104,3 ± 11,6; p=0,02, respectively). The LV stroke volume and ejection fraction was likewise lower with mode 2 as compared to mode 1 by echocardiography and RNV (53,2 ± 9,4 vs 64,2 ± 11,3; p=0,008, 43,8 ± 6,3 vs 54,9 ± 7,2; p=0,004 and % 55,1 ± 5,1 vs % 59,1 ± 4,5; p=0,003 and % 46,8 ± 7,4 vs % 52,9 ± 7,3; p=0,008, respectively).Myocardial perfromance index (MPI) was similar when measured at the lateral tricuspid annulus (0,46 ± 0,14 vs 0,47 ± 0,12; p=0,71) but was higher when measured at the lateral mitral annulus in mode 2 as compared to mode 1 (0,51 ± 0,06 vs 0,42 ± 0,05; p=0,001). Tricuspid annular plane systolic excursion values were similar in the 2 pacing modes (21,8 ± 2,3 vs 20,9 ± 1,1; p=0,13).The LV electromechanical delay, interventricular electromechanical delay and interventricular dyssynchrony values were higher in mode 2 as compared to mode 1 (73,4 ± 28,5 vs 23,4 ± 12; p<0,001, 49,4 ± 20,3 vs 7,1 ± 12,7; p<0,001, 38,8 ± 12,1 vs 1,8 ± 3,7; p<0,001, respectively).All the studied systolic and diastolic function parameters regarding the right ventricle were similar in the 2 pacing modes by both echocardiography and RNV.Conclusion: In patients with structurally normal hearts and dual chamber pacemakers implanted for SSS, a switch from intrinsic AV conduction to right ventricular apical pacing acutely resulted in a decrease in LV enddiastolic and stroke volumes and EF, an increase in the left atrial diameter and the MPI and led to a higher level of intra- and interventricular dyssynchrony.