Cardiac output is a sensitive indicator of difference in exercise performance between single and dual sensor pacemakers.

Although multisensor pacing may compensate the inadequacy of rate adaptation in a single sensor system, the clinical role of multisensor driven rate adaptive pacing remains unclear. We compared the performance between single sensor and dual sensor driven pacemakers using exercise cardiac output (CO) as a marker of cardiac performance. Eight patients with a mean age of 63 +/- 3 years implanted with a dual sensor pacemaker driven by combined activity (ACT) and QT interval sensors were studied in the ACT-, QT- only and the dual QT + ACT-VVIR modes. Patients performed submaximal and maximal exercise tests with CO assessed by carbon dioxide rebreathing method. Comparing the HR response based on the change in metabolic workload, the ACT-VVIR "overpaced," the QT-VVIR "underpaced," and the QT + ACT-VVIR achieved the best approximation to normal. The percentages of CO increase in ACT-VVIR and QT + ACT-VVIR modes over resting CO were higher at 1 minute of exercise (295 +/- 85% and 165 +/- 49%, respectively) compared to the QT-VVIR mode (81 +/- 40%, P < or = 0.05). During exercise, stroke volume changes from baseline were similar between ACT-VVIR and QT + ACT-VVIR modes, but a compensatory increase in stroke volume occurred in the QT-VVIR mode during submaximal exercise (50 +/- 11 mL vs 24 +/- 17 mL in the QT + ACT-VVIR and 14 +/- 4 in ACT-VVIR, P < or = 0.003). There was no difference in the maximal exercise workload, exercise duration and CO at the submaximal and maximal exercise between the 3 sensor modes. Thus, exercise capacity is a poor indicator of sensor performance while CO measurement is a sensitive indicator of sensor mode differences especially at low workload exercise. The ACT-VVIR gave the fastest increase in CO at start of exercise at the expanse of overpacing, whereas the "under-paced" QT-VVIR compensated for the slower rate increase by utilizing contractility reserve during submaximal exercise. Dual sensor pacing, by achieving the best heart rate to workload relationship, provided a CO response without overpacing or using contractility reserve during exercise.