Cross talk detection in the ventricular channel can cause asystole. Following conditions predispose to cross talk inhibition of the ventricular channel:

Short ventricular blanking period
High atrial output
High ventricular sensitivity

Atrial cross talk is known as far field R wave oversensing. This can cause automatic mode switching because the sensed atrial rate is high. This can be prevented by programming the post ventricular atrial refractory period (PVARP) to a higher value.

Intrinsicoid deflection is recorded in the surface ECG and intrinsic deflection is recorded directly from the heart. Intrinsic deflection can be recorded in experimental settings or by the intracardiac electrodes in pacemakers.

Ventricular blanking period

Ventricular blanking period is the period after the atrial stimulus during which the ventricular sensing circuit does not sense. This is programmed to prevent far field sensing of the atrial stimulus by the ventricular circuit. A spontaneous ventricular impulse occuring during the blanking period is not sensed and hence the pacemaker will deliver a ventricular stimulus, which does not capture the ventricle as the stimulus occurs during ventricular refractory period of the spontaneous beat.

Functional non capture

Capture does not occur as the stimulus is delivered during the refractory period. This can cause pseudofusion or loss of capture depending on the timing of the stimulus. The slew rate will be low in bundle branch block and can cause pseudofusion. A spontaneous impulse occurring during the ventricular blanking period can cause pacing stimulus delivery during the refractory period of the ventricle following the beat causing loss of capture.

Slew rate
Slew rate is the rate of rise of the spontaneous impulse. A slow rising impulse like P wave has a low slew rate which QRS complex which is a rapidly rising wave has a high slew rate. Slew rate of QRS can be low in bundle branch block.