Physical principles of artificial stimulation of the heart : Stimulation of the canine heart in situ

1. 1. In artificial heart stimulation, the essential quantity is the density of current, , in the intramyocardial wall. Dosage of the pulse amplitude in volts can have serious consequences for the patient. Curve indications in volts on pacemakers and in publications and records must, therefore, be rejected. 2. 2. Hence, the pacemaker should supply stabilized current pulses even while the load impedance is increasing. 3. 3. The distortion of the voltage curve at stabilized current is an electrode effect. 4. 4. Separate measurement and registration of the physical quantities involved in stimulation is advisable. The values obtained in every individual patient warrant conclusions as to the method of choice. It is recommended that one start with the Furman and Schwedel method, i.e., with one electrode in the right ventricle and the other placed subcutaneously in the thorax (a noncritical location). 5. 5. Measurements on the canine heart in situ with block, carried out with currents pulses of rectangular configuration, revealed that, when the Furman method is used, chronaxy and rheobase of the myocardium are dependent on the position of the electrodes. 6. 6. The phase which the heart is in when the current pulse is supplied is a factor of importance for the heart's following of the imposed frequency rate