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Biomedical subjects

W A Tacker

Publications and source records attributed to W A Tacker.

132 records · Page 8Linked to original sources
PubMedDate not supplied

Effects of myocardial infarction on catheter defibrillation threshold.

Because the automatic implantable defibrillator may be used in patients having ischemic heart disease, it is important to know whether myocardial ischemia changes the threshold for ventricular defibrillation under experimental conditions simulating automatic internal defibrillation. We determined changes in ventricular defibrillation threshold following coronary occlusion, using an electrode catheter designed for use with an automatic implantable defibrillator. Acute myocardial ischemia was produced without thoracotomy in 10 dogs (experimental group) by embolization with a plastic bead injected via a catheter into the left coronary artery. A control group of 4 dogs had only saline injected into the artery. Defibrillation threshold was measured at 15-min intervals from 1 hour before embolization to 2 hours after embolization. In the control group, voltage, current, energy, and impedance were unchanged after injection of saline into the coronary artery, and india ink perfusion revealed no ischemic areas. In the experimental group postembolization threshold current and energy were significantly higher than preembolization values: 0.47 vs 0.40 A/kg and 1.01 vs 0.80 J/kg, respectively (p less than 0.01). The magnitude of the peak change in threshold current after embolization was positively correlated (r = 0.79) with the size of the ischemic zone, determined by weighing unstained areas after india ink perfusion. Defibrillation threshold for a catheter electrode configuration increases for at least 2 hours following onset of acute myocardial ischemia. This finding must be accounted for in the design and use of an automatic implantable defibrillator.

Animals↗
PubMedDate not supplied

An animal model for testing automatic defibrillators.

A promising therapy for ventricular fibrillation--a life-threatening cardiac arrhythmia--is implantation of an automatic defibrillator. A critical component of such a device is the system that detects the presence of ventricular fibrillation. Automatic systems for detecting ventricular fibrillation have been tested with arrhythmias produced by electric shocks in normal canine hearts, but have not been tested with spontaneous arrhythmias in hyperirritable hearts. We have developed an animal model to create arrhythmias without electrical stimulation and have used it to test our automatic defibrillator. This model permits evaluation of both reliability to diagnose VF and reliability to reject other tachyarrhythmias.

Animals↗
PubMedDate not supplied

Optimal spacing of right ventricular bipolar catheter electrodes for detecting cardiac pumping by an automatic implantable defibrillator.

Our defibrillation-detecting system uses both ECG and right ventricular impedance change (delta Z). We studied the effect of catheter electrode spacing on delta Z in 10 dogs with body weights of 10 to ,5 kg and heart weights of 67 to 220 g. Impedance to 20-kHz 100--muA square waves was measured between two 1-cm-long electrodes mounted on a No. 12F catheter and wedged into the right ventricular apex. Catheters with spacings of 5 to 25 mm between the electrodes were tested during sinus rhyhm and ventricular fibrillation. During sinus rhythm the mean beat-to-beat delta Z was 23 +/- 4 omega using the 5-mm spacing. Wider spacing gave smaller, and hence less desirable, delta Z. Some delta Z signals were recorded during ventricular fibrillation, and 5-mm spacing was more sensitive to these than wider spacing. This resulted in some prolongation of the time between onset of fibrillation and application of the defibrillation shock, but should decrease false positive diagnosis of fibrillation. No clear relationship was observed between delta Z and body weight or heart weight. We conclude that the 5-mm spacing is best for detection of pumping by the catheter-impedance method in hearts of this weight range.

Animals↗
PubMedDate not supplied

Hemodynamic responses to two defibrillating trapezoidal waveforms.

The purpose of this study is to compare postdefibrillation hemodynamics following a 2-msec 80% tilt shock to those following a 10-msec 50% tilt shock. The waveforms can be generated by an automatic implantable defibrillator. In 18 mongrel dogs, a defibrillating catheter carrying two pairs of electrodes was lodged at the apex of the right ventricle. Every 15 min a fibrillation-defibrillation episode was initiated, alternating the two defibrillating waveforms in successive episodes. The peak current for the 10-msec defibrillating shock was twice the predicted threshold peak current; the 2-msec shock was of the same delivered energy as the 10-msec shock. In each episode, fibrillation lated for 30 sec, then defibrillation was accomplished with one of the two wave-form countershocks. Hemodynamic measurements were recorded at 2 min prior to fibrillation and 1 min after defibrillation of each episode. Data were obtained on heart rate, mean femoral arterial blood pressure, cardiac output, left ventricular dP/dt, right ventricular dP/dt, cardiac power, and the number of ventricular ectopic beats per minute. The data indicate that with superior restoration of circulation as the criterion, a low-peak-current, long-duration, low-tilt defibrillating waveform is preferable for catheter-electrode ventricular defibrillation.

Animals↗
PubMedDate not supplied

Detection of pulse and respiratory signals from the wrist using dry electrodes.

A dry, tetrapolar electrode array was used to detect the differential impedance signal at the wrists of 11 adult human subjects. Experiments were conducted to determine the importance of potential-sensing electrode spacing to detect each wearer's pulse rate and respiratory rate. The current-injecting electrodes were at the sides of the wrist; the potential-sensing electrodes were on the volar wrist surface. The bandwidth-filtered root-mean-square amplitudes of the pulse and respiratory components were computed and found to increase with increasing electrode spacing. Optimum spacings were slightly different for the pulse and respiration and were slightly different in the male and female subjects. A spacing for the potential electrodes of about 60% of the wrist hemicircumference is a good compromise for detecting respiration and pulse.

Adult↗