Mechanical factors and the electrocardiogram

Early Failures of Permanently Implanted Transvenous Pacemaker Systems: Spontaneous Recovery of Sensing Function in Three of Twelve Cases

“…Electrophysiologic studies have demonstrated a transient increase in stimulation threshold with a subsequent decrease and plateau early after endocardial electrode placement. This is believed to result from local injury and fibrosis at the catheter tip (15). Certain circumstances may exacerbate this problem, e.g., subendocardial myocardial infarction (13), metabolic and electrolyte disturbances, or drug therapy (16).…”

Atrial Systole and Ineffective Pacemaker Stimuli

“…The efficacy of ventricular capture may be enhanced or diminished by atrial activity. The two hypotheses which have been proposed to explain this phenomenon are (1) the eleclrotonic mechanism (Wedensky facilitation or inhibition) and (2) the mechanical mechanism. We present a case in whicb ventricular capture by a stimulus from a programmable VVI pacemaker was prevented by a preceding P-wave.…”