Intrinsic deflection and intrinsicoid deflection
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.