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Biomedical subjects

S Furman

Publications and source records attributed to S Furman.

At least 19 recordsLinked to original sources
PubMed1992

Precision of impedance cardiography measurements of cardiac output in pacemaker patients.

Objective hemodynamic assessment of pacemaker patients is necessary for gauging responses to changes in programming or other conditions that affect the circulation. Impedance cardiography permits noninvasive, repetitive determinations of cardiac output at short intervals, but data regarding variability of this method in patients with pacemakers is unavailable. Thirty-eight patients with implanted pacemakers (24 DDD, 14 VVI) and six normal subjects were studied. A computerized impedance cardiograph was used to calculate cardiac output from the product of the first derivative of the thoracic impedance signal (dZ/dt), the ventricular ejection time, and heart rate. Each patient was studied while supine after a period of at least 15 minutes of rest and repeated impedance measurements (about ten) were performed. Fourteen patients were studied in sinus rhythm, 24 were studied during DDD pacing, and 32 patients were studied during VVI pacing. Cardiac and stroke indices were calculated 706 times on the basis of 11,296 accepted beats. Variability was assessed by methods that analyzed serial measurements and variability between two consecutive and nonconsecutive measurements. The mean indices and coefficients of variation of two measurements and of serial measurements in sinus rhythm and during DDD pacing were 4%; in VVI it was 6%. The precision of impedance cardiography in all pacing modes, as demonstrated by analysis of variability, indicates that detected changes of stroke volume and cardiac output > 7% on serial (two and more) measurements, performed by the same operator and during the same session, represent true hemodynamic alterations with 95% confidence.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1992

Orthostatic responses in patients with DDD pacemakers: signs of autonomic dysfunction.

UNLABELLED: Responses to orthostasis may be altered in states associated with autonomic dysfunction. Computerized impedance cardiography, a noninvasive method for continuous assessment of stroke volume and mean blood pressure, was utilized to study the postural hemodynamic changes in eight normal and 27 patients with DDD pacemakers. Twenty patients with complete heart block (five with heart failure) were studied in the VDD mode and seven patients with sick sinus syndrome were assessed in DVI (four) or VDD (three). The results with pacemaker patients are significantly different from those observed in normal. Pacemaker patient responses to standing included: (1) a reduction in systolic, diastolic, and mean blood pressure; (2) an increase in heart rate in patients with intact sinus node function and no change in patients with sick sinus syndrome; and (3) stroke volume was unchanged in patients with sick sinus syndrome or heart failure and only modest reduction occurred in the remaining patients. CONCLUSIONS: (1) No reduction in stroke volume during upright posture occurs in DDD patients with sick sinus syndrome and this appears to be a compensatory reaction to an inadequate heart rate response to standing; (2) The hemodynamic response of DDD patients to the assumption of an upright posture is consistent with autonomic dysfunction; and (3) The primary cause for autonomic dysfunction in DDD patients may be the asynchronous ventricular depolarization caused by right ventricular pacing.

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PubMed1992

The clinical relevance of electromyopotential oversensing in current unipolar devices.

UNLABELLED: Electromyopotential oversensing of unipolar pacemakers was first appreciated 20 years ago, but its prevalence in present day devices is less well defined. Thirty-four pacemaker patients, only two with symptoms suggestive of oversensing, were evaluated in unipolar settings to assess the frequency of provocation of oversensing in one or, if present, both pacing channels. The sensing threshold of each patient, whenever possible, was recorded as well. RESULTS: Atrial oversensing occurred in 11/18 patients (61%), all at sensitivities in the 0.4-1.0 mV range. Ventricular oversensing was noted in 13/33 patients (39%), with all but one programmed to settings of 1.25 mV or more sensitive (i.e. < 1.25 mV). Twenty six of 26 patients amenable to testing had ventricular sensing thresholds of at least 4.0 mV or more. Of the 15 patients amenable to atrial sensing threshold testing, 4 had a threshold of 1.0 mV or < 1.0 mV, 6 had thresholds between 1.0-2.0 mV, and 5 sensed at settings > 2.0 mV. CONCLUSION: Electromyopotential oversensing remains a relevant issue in current day unipolar pacemakers. Most patients do not describe symptoms related to electromyopotential interference, yet such interference is frequently provoked. Oversensing is common at high sensitivities typically utilized for atrial sensing, but quite unusual at settings necessary for adequate ventricular sensing. Programming unipolar devices to unnecessarily high sensitivities should be avoided or serious consequences may result.

Cardiac Pacing, Artificial↗
PubMed1992

Electrophysiological effect of the maze procedure on canine sinoatrial node function.

The maze procedure is an operation that has had great initial success in curing atrial fibrillation. This procedure includes several right atrial incisions that may interrupt the integrity of the sinoatrial node or its arterial supply. To assess the effect of the maze procedure on sinus node function (SNF), the following studies were performed: sinus node recovery times (SNRT), corrected SNRT (CSNRT), CSNRT under autonomic blockade maximal heart rate and intrinsic heart rates. Thirty-four dogs underwent a right thoracotomy with cardiopulmonary bypass (CPB). The dogs were divided into three groups. Group 1 (n = 9), the sham group, underwent CPB without any incisions. Group 2 (n = 8) underwent CPB and one of the right atrial incisions. Group 3 (n = 18) underwent CPB and all three of the right atrial incisions. SNF was determined before and after the procedure. Groups 1 and 2 had no significant difference in measured SNF acutely after the procedure. In Group 3 the mean SNRT increased from 552 msec to 1,984 msec (P = 0.005). Sinus node dysfunction was corroborated by all studies. In the chronic studies, a trend toward recovery of SNF was observed. The maze procedure results in significant acute sinus node dysfunction. This dysfunction may resolve spontaneously over the ensuing months. Modifications of the maze procedure that avoid the sinus node or its blood supply area may reduce procedure related sinus node dysfunction.

Animals↗
PubMed1992

Clinical evaluation of the safety of repetitive intraoperative defibrillation threshold testing.

One goal of the initial implantation procedure for a cardioverter defibrillator is determination of the configuration and patch location with the lowest defibrillation threshold (DFT). To determine the safety of multiple defibrillation tests, an analysis of the intraoperative defibrillation threshold tests (DFTT) in our patients was performed. In 84 patients, the mean number of DFT trials was 5.27; the mean number of joules received was 275.0. The maximum number of shocks in one implant procedure was 50 for a total of 4,895 joules without complications. Four patients received 30 or more DFT shocks without complication. There were two complications related directly to the DFTT: one patient with severe noninflammatory cardiomyopathy developed electromechanical dissociation and was subsequently resuscitated and survived; the second patient with severe triple vessel coronary artery disease suffered an intraoperative myocardial infarction during testing and eventually died 22 days postoperatively. All patients received an ICD unit; six patients had DFTs of greater than 20 joules. Based on our experience, we followed the clinical status (heart rate, blood pressure, ECG changes, fluid status, total anesthesia time) during the DFTT to determine the extent and duration of our testing protocol. Multiple shocks due to repositioning of the leads in a stable patient should not prohibit extensive testing as adverse consequences do not appear to be cumulative.

Electric Countershock↗
PubMed1992

Cardiac pacing and atrial arrhythmias.

Pacemaker patients frequently have concomitant atrial tachyarrhythmias, most importantly atrial fibrillation, because numerous underlying electrical or structural diseases can potentiate both conditions. DDD pacing (or atrial) appears superior to VVI in limiting the occurrence of atrial fibrillation and its associated negative sequela. Sick sinus syndrome, a prior history of atrial fibrillation, and advanced age predispose patients with DDD devices to postimplant atrial fibrillation, yet the majority of these high-risk patients are manageable in DDD throughout their follow-up. DDD patients at significant risk for developing atrial arrhythmias require special attention regarding the selection and programming of their devices. Rate modulation, higher lower rate limits, special approaches toward upper rate limit management, and antitachycardia capabilities may all be important aspects in their management. The combined use of AV node ablation and ventricular or DDD pacing to manage patients with refractory atrial tachyarrhythmias is becoming an increasingly accepted therapeutic approach.

Atrial Fibrillation↗
PubMed1979

The autodiagnostic pacemaker.

Loss of normal pacemaker stimulation and/or sensing functions requires prompt detection, automatic correction, and automatic and continuous "marking" of the intermittent failure. The autodiagnostic pacemaker (ADP) detects "failure to capture" (FC) by distinguishing, at its single stimulating and sensing electrode, between the normal biphasic cardiac response evoked by an adequate stimulus (corresponding to the QRS and T waves on the surface cardiogram) and the monophasic pseudo-response generated by electrotonic spread of a subthreshold stimulating current. Detection of "failure to sense" (FS) spontaneous cardiac activity requires two amplifiers: a "timing control" amplifier of standard fidelity and standard (approximately 250 ms) refractory period, and a second amplifier which has negligible refractoriness and provides high fidelity amplification of all evoked and spontaneous activity. Failure to sense (FS) is defined as a specified number of consecutive failures to recycle correctly the pacemaker's timing circuits. Similarly, a specified number of consecutive failures of the stimulus to evoke an active cardiac response is defined as a failure to capture (FC). When FC is detected, the ADP doubles the applied stimulus voltage and generates marker pulses which follow every subsequent stimulus by 40 ms. The marker pulses appear on the surface electrocardiogram, serving as an externally detectable "memory" of the earlier, possible corrected, failure. When FS is detected, non-stimulating marker pulses, of a different time relation (80 ms delay) to each stimulus, are generated continually and can also be detected externally. The ADP has been tested in 14 anesthetized, open-chest dogs. Unipolar rather than bipolar electrodes were used as they rpovided more reliable stimulation and more satisfactory electrograms for detection.

Animals↗
PubMed1979

Nuclear pacemakers.

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Electric Power Supplies↗
PubMed1979

Comparison of active and passive adhering leads for endocardial pacing.

The frequency of lead failure requiring invasive correction in a total of 276 implants of four different transvenous leads (6907, continuous lead, IE-65-I, and MIP 2000) was observed during a one-and-one-half year period with a minimum of two months follow-up post-implant. Implants were on a successive sequential basis, randomly distributed between the two surgeons normally performing implants, and unselected for presumed ease or difficulty of the procedure. Failure rates with the 6907 and continuous leads were 7 of 76, or 9.2%; with the IE-65-I, 2 of 76, or 2.6%; and with the MIP 2000, 8 of 45, or 17.8%. The difference between the IE-65-I and the two conventional leads was significant at the 5% level, and between the IE-65-I and the group of the other three at the 1.6% level. The MIP 2000 was significantly different from the other three leads at the 2.7% level. Previous clinical experience with 849 implants with continuous and 6807 leads indicated that the overall data was similar to that obtained in the present evaluation. No significant differences in failure rates between surgeons and no measurable "practice effect" could be detected. It was concluded that the design of the lead is a major factor in the differing need for early secondary intervention.

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