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Pacemaker. QT interval (QTI) may change when cardiac junction is improved by optimizing the AV delay. QTI is used as the sensor for rate responsive pacemakers. Evoked (e)QTI is measured as the time duration from the ventricular pace-pulse to the T sense point, which is the steepest point of the intracardiac T wave. The relationship between AV delay and eQTI and cardiac function was studied in 13 patients (74.2 ± 9.3 [SD] years old) with an implanted QT-driven DDDR pacemaker. A special pacemaker software module was downloaded into the pacemaker memory for eQTI data logging. AV delay was set at 100, 120, 150, 180, 210, and 240 ms. Cardiac output (CO) was measured by' continuous Doppler echocardiography eQTI was 343.3 ± 22.5, and 343.4 ± 23.2 ms (P < 0.01. repeated ANOVA) and CO was 4.2 ± 0.8, 4.6 ± 0.8, and 4.2 ± 0.8 L/min (P < 0.0001, repeated ANOVA) when AV delay was set at the AV delay shortened by one step (AV[-]) and prolonged by one step (AV[+]) from the AV delay at which QT interval was maximum (AV[max]) in seven patients, in whom the peak AV delay at which the eQTI was maximal could be identified. eQTI decreased from 345.1 ± 20.9 to 339.4 ± 21.1 ms (P < 0.0001) and CO decreased from 4.4 ± 1.4 to 4.1 ± 1.3 L/min (P <0.005) when AV delay was prolonged from AV(max) to AV(+) in all patients. eQTI decreased from 345.1 ± 22.5 to 343.3 ± 22.4 ms (P < 0.0005) and CO decreased from 4.6 ± 0.8 to 4.2 ± 0.8 L/min (P < 0.05) when AV delay was shortened from AV(max) to AV(-) in seven patients. Thus, CO was maximal when AV delay was set at the AV delay at which eQTI was maximal. In conclusion, the optimal AV delay can be predicted from the eQTI sensed by an implanted pacemaker. and automatic setting of the optimal A V delay can be achieved by the QT sensor of an implanted pacemaker. [ABSTRACT FROM AUTHOR]