Does increasing sensitivity settings and lengthening ventricular refractory period cause loss of atrial signal detection in Cosmos II pacemakers?
A software logic error in Cosmos II pacemakers causes loss of atrial signal detection at high sensitivity settings, which can be avoided by keeping the ventricular refractory period at or below 210 msec.
A logic error in the software of Cosmos II results in apparent malsensing of atrial signals at high rather than low sensitivity settings. The paradoxical function was found in 54 out of 87 units tested (= 62%) if the atrial sensitivity was increased and in 54 out of 87 units tested (= 62%) if the atrial sensitivity was increased and the ventricular refractory period was lengthened beyond critical limits that could be defined individually. The problem inherent in both unipolar (66%) and bipolar systems (54%) is attributed to a summation of a physiological signal and internal noise, which has to be detected at the atrial level within a specific timing window to disable atrial sensing for the next pacing cycle. The malfunction virtually disappears if the ventricular refractory period does not exceed 210 msec. It is recommended, therefore, that Cosmos II pacemakers be left at their nominal ventricular refractory value (200 msec).
Fröhlig et al. (Mon,) studied this question.