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Biomedical subjects

S Furman

Publications and source records attributed to S Furman.

At least 163 records · Page 9Linked to original sources
PubMed1986

Selective atrial sensing in dual chamber pacemakers eliminates endless loop tachycardia.

With the introduction of dual chamber pacemakers that have multiple atrial amplitude sensing values, selective P wave sensing is possible. Five consecutive patients were studied who had 1) retrograde atrioventricular conduction, 2) anterograde atrial signals that were at least 1.4 times larger than their corresponding retrograde atrial signals, and 3) dual chamber pulse generators that are capable of discriminating this difference in atrial amplitude. In each patient the pacemaker was programmed in the DDD mode and the postventricular atrial refractory interval was at least 100 ms shorter than the individual's minimal retrograde conduction time. Two atrial sensitivity settings were evaluated in each patient: a high setting to ensure sensing of both anterograde and retrograde P waves, and a lower setting to allow sensing of anterograde P waves only. Ambulatory electrocardiographic monitoring demonstrated that with a high sensitivity setting, each patient sustained endless loop tachycardia (mean number of episodes 41, range 6 to 143) and that a low atrial sensitivity setting eliminated the tachycardia. With the lower atrial sensitivity setting, there was only sporadic atrial undersensing (1.5 episodes for each 1,000 P waves). This study demonstrates that atrial signals having different amplitudes can be selectively sensed. Additionally, dual chamber pulse generators with multiple atrial amplitude sensitivity values can discriminate anterograde from retrograde P waves, ensure anterograde sensing, reject retrograde P waves and eliminate endless loop tachycardia.

Aged↗
PubMed1986

Spontaneous endless loop tachycardia.

Pacemaker-mediated endless loop tachycardia is usually caused by a P wave displaced from the physiologic position preceding a QRS complex to a time of atrial channel sensitivity after the QRS. Five cases are described of endless loop tachycardia starting after a normally-timed P wave, either spontaneous and preceding a ventricular stimulus or a P wave produced by an atrial channel stimulus followed by a ventricular stimulus and QRS complex. In each instance, the atrial refractory interval (ARI) was shorter than the retrograde conduction time. In four of the cases, prolongation of the atrial refractory interval after the ventricular event ended the tachycardias. In the fifth, in which the pulse generator could not be so programmed, the ventricular inhibited mode was required.

Adult↗
PubMed1986

Bipolar pacing.

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Electrophysiology↗
PubMed1986

Pacemaker infection.

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Bacterial Infections↗
PubMed1986

Interatrial conduction during cardiac pacing.

DDD pacemakers sense and pace right-sided cardiac chambers. The relationship of atrial to ventricular systole on the left side of the heart is of importance for systemic hemodynamics. Effective atrioventricular synchrony is partially determined by interatrial conduction time (IACT). At the time of DDD pacemaker implantation, interatrial conduction was measured using an intraesophageal pill electrode in 25 patients who were on no cardiac medications. Mean interatrial conduction time for all patients prolonged from 95 +/- 18 ms during sinus rhythm to 122 +/- 30 ms during right atrial pacing (p less than 0.001). In 16 patients with P wave duration less than 110 ms interatrial conduction prolonged from 85 +/- 10 ms during sinus rhythm to 111 +/- 9 ms during right atrial pacing (p less than 0.01) compared to 114 +/- 20 ms prolonging to 111 +/- 19 ms (p less than 0.01) in 9 patients with P wave duration greater than 110 ms. In each patient, while atrioventricular conduction prolonged with incremental right atrial pacing, interatrial conduction times did not vary. Interatrial conduction prolongs from baseline during atrial pacing and remains constant at all paced rates from 60-160 beats per minute. In addition to longer interatrial conduction times during sinus rhythm, patients with electrocardiographic P wave prolongation have longer interatrial conduction times during right atrial pacing than do normals (p less than 0.001). Based on interatrial conduction times alone, the AV interval during DDD cardiac pacing should be approximately 25 ms longer during AV pacing as compared to atrial tracking.

Aged↗
PubMed1986

The dynamic nature of ventriculoatrial conduction.

An endless loop tachycardia starts when the atrial sensory amplifier of a dual chamber pacemaker identifies an early atrial signal originating from a ventricular or atrial premature depolarization or from myopotential noise. The tachycardia will continue as long as ventriculoatrial conduction is sustained. By selecting the appropriate atrial sensitivity setting, postventricular atrial refractory period, or upper rate limit, it is possible to eliminate sustained endless loop tachycardia. Electrophysiological data obtained at the time of dual chamber pacemaker implantation can assist the physician when selecting these settings. This report summarizes our intraoperative data on ventriculoatrial conduction obtained from 432 consecutive patients. One hundred sixty-two patients had evidence of ventriculoatrial conduction including 14% of patients with antegrade complete heart block and 32% with 2:1 AVB. The majority of patients with preserved antegrade conduction had sustained retrograde conduction. During incremental ventricular pacing, ventriculoatrial conduction prolonged in the majority of patients, and with faster ventricular pacing rates, ventriculoatrial block developed. Ventriculoatrial block developed in half of the patients at a ventricular pacing rate exceeding 120 bpm. Analysis of these data suggests that by selecting an upper rate limit of 140 bpm, a postventricular atrial refractory period of 300 msec, and an atrioventricular interval of 125 msec, approximately 90% of patients will not have sustained endless loop tachycardia.

Aged↗
PubMed1986

Measurement of differences in timing and sequence between two ventricular electrodes as a means of tachycardia differentiation.

The use of two ventricular sensing electrodes to determine electrical activation sequence could provide a method for differentiation of normal from abnormal rhythms by implantable antitachycardia devices. Simultaneous recordings from two ventricular sites were obtained during dual chamber pacemaker implantation (5/8 patients), cardioverter-defibrillator implantation (2/8 patients), or programmed electrical stimulation study (1/8 patients). Recordings were made in normal sinus rhythm (NSR) (5 beats each in 8/8 patients), during ventricular tachycardia (VT) (38 beats with 7 morphologies in 3 patients) and during premature ventricular contractions (PVCs) (20 beats with 8 morphologies in 6 patients). Leads were placed transvenously in the right ventricle in 6 patients, and epicardially on the left ventricle in two. Intervals between the intrinsic deflection of the two ventricular electrograms ranged from 0 to 91 ms (mean of 26 ms) during NSR, from 13 to 141 ms (mean of 66 ms) during VT, and from 10 to 72 ms (mean of 40 ms) during PVCs and were reproducible within each patient for each type of rhythm. In all patients, the difference in sequence and timing between the dual electrograms in NSR beats vs. ectopic beats allowed for the differentiation of normal and abnormal complexes. These differences in each patient ranged from 23 to 210 ms (mean of 81 ms) during VT and from 3 to 89 ms (mean of 44 ms) during PVCs. Fourteen of the 15 ectopic morphologies exhibited greater than 20 ms difference in timing compared to their corresponding NSR beats. Combined with the appropriate software, multiple ventricular leads may be used by antitachycardia devices to discriminate between normal and abnormal ventricular activity.

Aged↗
PubMed1986

Simplifying pacemaker follow-up by the implementation of the NASPE standards on computer interface. North American Society of Pacing and Electrophysiology.

One of the basic limitations for the development and use of more sophisticated pacemakers is the difficulty to provide adequate instrumentation and methodology for the follow-up in the clinical environment. To address this problem, the NASPE (North American Society of Pacing and Electrophysiology) Computer Committee has developed an interface standard to allow communication with the pacemaker programmer through many computer systems. The document recommends the use of the RS 232/c (CCITT V.24) interface with baud rates variable from 300 to 19,200, 7 bit word, no parity and Xon/Xoff protocol. The actual message format consists of an SOH code, a function code describing the action to be taken, a variable code defining the parameter on which the action is to be taken, and the actual numerical data. The CHECKSUM is calculated by summing all the ASCII codes beginning after the SOH code and ending with the last byte preceding the checksum itself. The last seven bits so calculated are attached to the message, and a consecutive ETX code ends the communication. At the receiving end, the checksum is recalculated and compared to the value received. If the two match, the message is accepted. Using this format, compatible computer software and pacemaker programmers can be developed independently and function as a unit. The protocol is capable of real-time ECG transmission.

Humans↗
PubMed1986

Implantable pacers for tachycardia termination: stimulation techniques and long-term efficacy.

The long-term efficacy of pacing for termination of supraventricular tachycardia (SVT) and ventricular tachycardia (VT) was reviewed. Increasingly complex and sophisticated antitachycardia pacing stimulation patterns have evolved, and are outlined. Although excellent results are reported with simple patterns, it may be that the more complex algorithms increase the percentage of tachycardia patients who may be candidates for implantation of a device. In the papers reviewed, there were 460 patients, 268 with SVT, and 192 with VT. Results were judged to be good-excellent in 96.5% of both VT and SVT groups.

Cardiac Pacing, Artificial↗
PubMed1985

Stability of atrial sensing and pacing after dual chamber pulse generator implantation.

The continued efficacy of dual chamber pacing is predicated on the stability of both atrial and ventricular electrodes. The introduction of the tined atrial J lead has decreased the incidence of atrial lead dislodgment, allowing for continued effective sensing and pacing. To study the evolution of atrial pacing and sensing threshold, 54 patients with identical pulse generators and atrial electrodes were evaluated for 58 +/- 29 weeks (mean +/- SD). Immediately after pacemaker implantation in 39 patients, the amplitude of the atrial signal was measured by programming the pulse generator to the lowest sensitivity that assured pacing in the atrial synchronous mode. Three levels of atrial sensing were possible: high (0.5 mV), intermediate (1.3 mV) and low (2.5 mV) sensitivity. Three patients had a high, 16 patients had a medium and 20 patients had a low atrial sensitivity. The P wave amplitude and slew rate measured on a physiologic recorder did not differ significantly between the latter two groups. The atrial charge threshold increased from 1.8 +/- 1.3 microcoulombs (microC) to a maximal value of 2.5 +/- 1.3 microC, 3 days to 1 week after implantation (p = 0.02). This remained elevated for 1 to 3 months (p = 0.05) and then decreased, remaining stable over the ensuing year. The atrial sensitivity for the group with noninvasive measurement did not change significantly, although there was considerable patient variation. For 54% of the patients, atrial sensing remained stable or improved. In 26% of the patients, further programming to higher sensitivity settings ws required. In the remaining 20% of the patients, the atrial sensitivity setting fluctuated.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1985

Endless loop tachycardia started by an atrial premature complex in a patient with a dual chamber pacemaker.

In a patient with a dual chamber pacemaker that senses in both the atrium and ventricle (VDD, DDD), a ventricular depolarization temporally displaced from a P wave can cause retrograde atrial activation and initiate an endless loop pacemaker-mediated tachycardia. A case in which an endless loop tachycardia was initiated by an end-diastolic atrial premature complex is reviewed. Retrograde conduction occurred because of the change in the temporal relation of atrial sensing and atrioventricular (AV) node depolarization. The implanted pacemaker did not have the capability of atrial refractory programmability. Atrial refractory interval extension, which occurs in this model after a ventricular premature complex to protect against a retrograde P wave, was not invoked since the tachycardia was begun by an atrial rather than a ventricular premature complex. The tachycardia was controlled by shortening the programmable AV delay. The mechanism of tachycardia induction and its management are outlined. Atrial refractory programmability is required in all VDD or DDD pacemakers.

Aged↗