Tibor A. Nappholz

Implantable automatic scanning pacemaker for termination of supraventricular tachycardia

Thirteen patients suffering from reentrant supraventricular tachycardia have undergone implantation of a scanning extrastimulus pacemaker. This pacemaker is fully implanted and automatic, and it requires no external control device to activate or control it. The pacemaker is activated when tachycardia occurs. After four cycles an extrastimulus is induced with a preset coupling time from a sensed intracardiac potential, and every four cycles thereafter a further extrastimulus occurs, but on each occasion there is a decrement in coupling cycle by 6 ms until 90 ms of the cardiac cycle has been scanned by extrastimuli. When necessary, two extrastimuli can be introduced with a fixed but preset coupling time between them. Every four beats two extrastimuli are induced but the coupling time between the spontaneous cardiac potential and the first stimulus is decreased by 6 ms until 90 ms of the cardiac cycle has been scanned. The coupling time between the two stimuli is fixed throughout the scan. When termination of tachycardia occurs the successful timing variables are retained in the pacemaker memory so that at the onset of the next episode of tachycardia these settings are used first. Pacemaker pulse width, sensitivity, tachycardia trigger rate, coupling intervals for both stimuli and the use of single or double extrastimuli are all programmable transcutaneously. Three patients required single, and seven patients double ventricular premature stimuli; three patients required double atrial premature stimuli for termination of tachycardia. Despite frequent attacks of tachycardia before implantation, only two patients had a sustained attack of tachycardia after pacemaker implantation.

Clinical Evaluation of an Adaptive Tachycardia Intervention Pacemaker with Automatic Cycle Length Adjustment

An exlernal version of a new pacemaker designed for automatic tachycardia termination is described. In response to a tachycardia, defined as four successive beats occurring at a rate faster than a variable preset value, a number of stimuli (1–15) are generated. The initial coupling interval and subsequent pacing cycle intervals (where applicable) are always the same. Failure to terminate tachycardia results in the reduction of the pacing cycle length by 6 ms before termination of tachycardia is re‐attempted. Pacing cycle length reduction may be repeated up to 16 times. If all coupling intervals of a single extrastimulus fail to achieve tachycardia termination, a second stimulus is scanned with the first through the same range of decrements. Additional stimuli, to a total of 15. could be used. A memory function is incorporated to retain and re‐use a successful sequence. The pacemaker was evaluated in 16 patients with recurrent “supraventricular” (atrioventricular and intra A‐Vnodal) tachycardia, using right ventricular pacing. Termination was successful in all patients. More than two stimuli were necessary in only two patients, one of whom required five, and the other six stimuli. No unwanted arrhythmias were induced. (PACE, Vol. 5, March‐April, 1982)

Detection of Ventricular Tachycardia Using Scanning Correlation Analysis

STEINHAUS, B.M., ET AL.: Detection of Ventricular Tachycardia Using Scanning Correlation Analysis. Cross correlation is an accurate method for distinguishing normal sinus rhythm (NSR) from ventricular arrhythmias. The computational demands of the method, however, have prohibited development of an implantable device using correlation. In this study, temporal data compression prior to correlation analysis was used to reduce the total number of computations. Unipolar and bipolar intracardiac electrograms of NSR and 23 episodes of ventricular tachycardia (VT) from 23 patients were obtained from a right ventricular apex electrode catheter during routine electrophysiology studies. The data were filtered (111 Hz), digitized (250 samples/sec) and temporally compressed to 50 samples/sec. Data compression removed four out of every five samples by only saving the sample with the maximum excursion from the last saved sample. The average squared correlation coefficient (r2) was computed for the NSR and VT episodes using each patients NSR waveform as a template. In all 23 patients, the r2 values showed large separation between NSR versus VT in both unipolar (0.93 ± 0.05 vs 0.20 ± 0.16, p < 0.005) and bipolar (0.91 ± 0.07 vs 0.17 ± 0.11, p < 0.005) electrode configurations using template lengths of 80% the intrinsic interval (avg ± SD). Narrow templates 40% intrinsic interval or less) often resulted in multiple r2 peaks during each heart cycle and degraded the r2 separation (n = 10, p < 0.005). High pass filtering at 3 Hz also degraded the r2 separation (n = 10, p < 0.05). Standard noncompressed correlations indicated that data compression had negligible effects on the results. Thus, a computationally efficient cross correlation method was found to be a reliable detector of VT. The results suggest that the T wave, as well as the QRS complex, is useful in VT recognition.

Detection of atrial activation by intraventricular electrogram morphology analysis: a study to determine the feasibility of P wave synchronous pacing from a standard ventricular lead.

The detection of atrial activation from a standard ventricular pacing lead with standard ventricular electrodes would provide patients with VVI and VVIR pacing systems atrial rate response and atrial synchrony. In addition to potentially increasing cardiac output appropriately in these patients at rest and during moderate exercise, P wave sensing with such a device could help reduce pacemaker syndrome. In this study, unipolar signals from distal and proximal intraventricular electrodes were recorded from the right ventricular apex in 20 patients. Unipolar eJectrograms from 16 patients were recorded using temporary electrophysiology catheters and in four patients using permanent pacemaker leads. Approximately 3 minutes of data per patient were acquired and analyzed. After selection of a P wave template, the difference in baseline normalized area between the template and signal was calculated on a point‐by‐point basis. The percent of atrial depolarizations correctly detected was determined for each patient and lead configuration at the optimal threshold. Far‐field P wave accuracy was better at the proximal electrode (74 ± 25%) than at the distal electrode (57 ± 34%) (P < 0.025). At the proximal electrode, 15/20 (75%) patients had > 70% accuracy and 11/20 (55%) patients had > 80% accuracy. At the distal electrode, 10/21 (48%) patients had > 70% accuracy and 7/21 (33%) patients had > 80% accuracy. In conclusion, far‐field detection of atrial activation at the ventricular proximal electrode appears possible with sufficient accuracy to provide periods of atrial rate response and synchrony in patients with a single standard lead.

Chronic Antithrombogenic Biomaterials Screen

The widespread usage of chronic implantable sensors in cardiac device systems has been hampered by both sensor technology issues and the lack of surface passivations with chronic antithrombogenic capabilities. In this study, dummy pacing leads with six types of passivations were implanted for 17 weeks in 36 dogs to assess thrombogenic character, degree of tissue growth and encapulation, and general performance in providing optically clear windows into the blood or body tissues. Asceptic surgical procedures were used and complete blood work‐up was performed every two weeks postop. Two dogs served as surgical shams to monitor system artifacts. At explant the devices fairly clearly divided themselves into two groups based on the percent of exposed surface area covered by gross macroscopic tissue accumulations. There were three passivated types in each group. Scanning election microscopy (SEM) and energy dispersive analysis of x‐rays (EDAX) techniques were used to investigate further the samples from the three passivation types that performed “better” based an percent surface area analysis. Issues that became prominent were substrate surface finish and topography, and some mineralization phenomena. Some of the evidence raises The possibility that processes that provide chronic antithrombogenic performance might also enhance mineralization or propensity toward natural breakdown processes. These questions are now being more closely addressed in follow‐up studies now in progress.