EFFECT OF PACING RATE ON REGIONAL LEFT-VENTRICULAR WALL-MOTION - ASSESSMENT BY QUANTITATIVE-ANALYSIS OF EQUILIBRIUM RADIONUCLIDE ANGIOGRAPHY

We evaluated the hemodynamic impact of right ventricular pacing at dif ferent stimulation frequencies. Fourteen patients with a right ventric ular pacemaker (VVI pacing with retrograde P wave) but without clinica l and electrocardiographic evidence of coronary artery disease underwe nt two equilibrium radionuclide angiographies: one under low heart rat e (50/60 beats per minute) and the other under fast heart rate (90/100 beats per minute). Left ventricular global and sectorial ejection fra ctions, amplitude and phase images of first harmonic, and sectorial ph ases of left ventricle were analyzed. In twelve patients (84.7%), sect orial ejection fraction abnormalities in the left ventricular apicosep tal and inferoapical regions were observed under low heart rate, and w orsened under fast heart rate, while new onset sectorial ejection frac tion abnormalities under fast heart rate were observed in the other tw o patients with normal sectorial ejection fraction under low heart rat e. Sectorial ejection fractions of left ventricular apicoseptal and in feroapical regions significantly changed between low and high heart ra te (-14.1 +/- 3.8%, p < 0.005; -7.5 +/- 2.4%, p < 0.01 respectively). Left ventricular sectorial phases were abnormal in only two patients ( 14.3%) under low heart rate, and in twelve patients (84.7%) under fast heart rate. Our study confirms that left ventricular regional wall mo tion abnormalities during VVI pacing significantly worsen under fast h eart rate in comparison to those under low heart rate.