Detection of ventricular fibrillation with a ventricular monopolar catheter electrode.

This report describes the use of right ventricular impedance (RVZ) sensing with a monopolar electrode to identify the cessation of pumping with the onset of ventricular fibrillation. RVZ, ECG (lead II), and femoral artery pressure were monitored in seven anesthetized dogs. An impedance recorder (10-kHz, 100-microA peak-to-peak current) was used to measure RVZ between a monopolar, catheter-mounted electrode placed in the right ventricle and an indifferent electrode (8.

Stroke volume and the three phase cardiac output rate relationship with ventricular pacing.

Knowledge of how stroke volume (SV), and hence cardiac output (CO), changes with ventricular pacing rate (R) constitutes a key aspect of sensor driven, variable rate pacemakers. It has been established that the relationship between CO and pacing rate exhibits three phases for rest and constant exercise. At low rates (phase 1), CO increases with increasing R; with additional rate increase (phase 2), CO either remains constant or increases slightly; and above some critical rate, CO decreases (phase 3).

Myocardial stimulation with ultrashort duration current pulses.

In order to identify a practical short-duration limit for stimulating myocardium, theoretical and experimental studies were carried out using dog and turtle hearts. The strength-duration curves for current, charge and energy were derived from the standard excitable membrane model which employs a parallel resistance and capacitance. From these derivations, the predicted duration for minimum energy was identified.