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Biomedical subjects

I Singer

Publications and source records attributed to I Singer.

At least 19 recordsLinked to original sources
PubMed1992

Interpretation of hypercalcemia in a patient with end-stage renal disease.

Patients with both end-stage renal disease and multiple myeloma are prone to changes in ionized calcium homeostasis that may have grave consequences. However, only total calcium level is reported in most routine laboratory testing, with various algorithms used to derive the physiologically important ionized or free calcium level to guide treatment. We studied a patient with multiple myeloma undergoing long-term hemodialysis who presented with a markedly elevated total calcium level but with only minimal elevation in the ionized calcium level. All of the commonly used algorithms would have overestimated the ionized calcium level, and some of these might have led to inappropriate treatment. When therapy depends critically on the ionized calcium level, direct measurement is essential.

Calcium↗
PubMed1991

Lateral thoracotomy for the automatic implantable defibrillator.

In 51 patients who required automatic implantable cardioverter defibrillator implantation without additional cardiac procedures, the lead system was implanted using a lateral thoracotomy approach, with complete muscle sparing in the last 24 patients. Exposure was excellent and allowed repositioning of leads for optimal defibrillation thresholds in 18 patients. Five of 19 patients who had previously undergone intrapericardial procedures required intrapericardial dissection for lead placement to provide satisfactory defibrillation thresholds. There were no intraoperative deaths or infarctions. The 30-day mortality rate of 3.9% was comparable with those in other series, and the use of muscle-sparing techniques and supplemental epidural anesthesia prevented pulmonary complications or the need for prolonged ventilatory support. We favor a muscle-sparing lateral thoracotomy incision for automatic implantable cardioverter defibrillator insertion, particularly in patients with a history of previous intrapericardial procedures.

Adult↗
PubMed1991

Contacts between hair cells in the avian cochlea.

In the avian papilla basilaris, contacts between hair cells are a common feature. With few exceptions, they only occur between tall hair cells (THC), and they are more frequent in the apical half of the papilla. In this quantitative study, four types of contacts are defined: Protrusion contacts, touch contacts, fusion contacts and multiple contacts. There are strong indications that these contacts are dynamic structures. The fact that avian hair cells probably communicate with each other means that their function can only be fully understood if cell groups are studied.

Animals↗
PubMed1991

Defibrillation efficacy using two low-profile endocardial electrodes.

The hypothesis that improved energy delivery and defibrillation efficacy can be achieved by using two widely separated endocardial electrodes and a cutaneous patch electrode was explored by positioning two 6.5 F electrodes (NuMed, Hopkinton, New York) with 5 cm platinum-iridium coils in the right ventricular apex (RVA) and the right ventricular outflow (RVO) in eight dogs. In another 12 dogs, an additional electrode was positioned in the RVA. A cutaneous patch (P) was placed at the cardiac apex. Biphasic pulses were delivered, the first pulse (6 ms) positive, the second negative (2 ms). The leading edge of the second was equal to the trailing edge of the first. RVO-/P+ and RVA-RVO-/P+ were compared with RVA-/P+ at a constant voltage setting required to achieve a 60% probability of success (P60) for RVA-/P+. At a constant voltage output, the probability of success for RVA-RVO-/P+ was significantly higher (81%) than RVO-/P+ (60%) or RVA-/P+ (67%) (p less than 0.03). The current delivered was greater for RVA-RVO-/P+ (9.9 +/- 2.3 amps) than for either RVA-RVO-/P+ (8.7 +/- 1.9 amps) or RVO-/P+ (9.0 +/- 2.0 amps) (p less than 0.0001). Similarly, the impedance was significantly lower for RVA-RVO-/P+ (66 +/- 12 omega) than for RVA-/P+ (75 +/- 12 omega) and RVO-/P+ (72 +/- 9.6 omega) (p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Is defibrillation testing safe?

Determination of defibrillation thresholds (DFTs) and implantable cardioverter defibrillator (ICD) testing requires repeated inductions of ventricular fibrillation (VF) and defibrillation attempts using known energy outputs. Little is known about the individual and cumulative effects of repetitive brief episodes of VF and hypoperfusion on cerebral function. The potential clinical utility of quantitative electroencephalographic (QEEG) monitoring during intraoperative ICD testing, by using processed 19-channel EEG (0.5-35 Hz bandwidth), was examined in ten anesthetized patients, five males and five females (mean age 62 +/- 10 years), who underwent ICD implantation and testing. Ischemic QEEG patterns were defined as those with a 3 standard deviation increase (P less than 0.01) in absolute delta (1.5-3.5 Hz) power persisting for greater than or equal to 2.5 minutes. The majority (80%) of the VF episodes (70) were accompanied by QEEG "slowing" (doubling of the pre-VF low frequency delta waves amplitude). All the patients (5/5) experiencing greater than 6 VF episodes showed a statistically significant increase in the low frequency amplitude. In contrast, this EEG abnormality was apparent in only one of five patients experiencing less than 6 VF episodes. These results suggest a cumulative QEEG depression associated with ICD testing. QEEG may provide an objective means for establishing an individualized upper safe limit of DFT testing and the total number of induced VF episodes.

Electric Countershock↗
PubMed1991

The initial clinical experience with an implantable cardioverter defibrillator/antitachycardia pacemaker.

Guardian antitachycardia pacing (ATP) 4210 is a third generation, multi-programmable cardioverter defibrillator undergoing Phase I clinical trials. The tiered response includes ATP, low energy cardioversion or defibrillation, and bradycardia support. Extensive telemetry is available, including an episode log and details of all episode events. Five patients underwent the implantation of Guardian ATP 4210 as part of a Phase I trial at the University of Louisville. Two of the five patients had multiple VT episodes that were reverted successfully using ATP pacing (slow VT) and defibrillation (fast VT) and VF episodes, which resulted in defibrillation therapy over a follow-up period of 6 to 8 months. Four of the five patients required bradycardia support for bradyarrhythmias unassociated with ATP therapy or defibrillation and one patient required bradycardia support postdefibrillation therapy. The device design is microprocessor based and requires continuous interrogation of the microprocessor memory and checks of the validity of programmed parameters to continue its operation. When the safety check fails, the device is designed to shut down its antitachycardia and defibrillator functions. This design feature has a potential for leaving the patient unprotected if the device shuts down. Modification of this feature is required to ensure the device's long-term safety.

Aged↗
PubMed1991

Effects of stress and beta 1 blockade on the ventricular depolarization gradient of the rate modulating pacemaker.

Prism-CLR is a closed loop, rate modulating pacemaker that uses ventricular depolarization gradient (Gd) to continuously adjust heart rate. Heart rate response to a formal mental stress protocol, esmolol (500 mcg/kg bolus, 75-125 mcg/kg/min infusion), and mental stress during esmolol infusion were studied in six patients to investigate if Gd and paced heart rate response are under direct beta-adrenergic control. Paced heart rates increased in response to mental stress in a physiological manner (P less than 0.001). Response to esmolol infusion was paradoxical, with increased paced heart rates during esmolol bolus and infusion (P less than 0.05). There was no significant alteration in either systolic or diastolic blood pressure during mental stress or esmolol infusion (P greater than 0.05). Paradoxical increase in paced heart rates during esmolol administration suggests a primary or secondary effect of esmolol to decrease the ventricular depolarization gradient. This hypothesis was supported in four dog studies in which direct Gd measurements were made during esmolol infusion. Mental stress during esmolol infusion resulted in significantly increased paced heart rates (esmolol effect) with blunted changes in heart rate in response to the mental stress. The results of this study suggest that the physiological rate response during mental stress is attributable to sympathetic autonomic response.

Adrenergic beta-Antagonists↗
PubMed1990

Low energy partial ablation of the atrioventricular node junction in the dog using a suction-ablation catheter.

A suction electrode catheter was used for low energy, partial ablation of the atrioventricular (AV) node junction in 12 dogs. In 10 dogs, partial injury of the AV node was induced. In six dogs, delivered energy was measured precisely with use of a specially designed electronic circuit. The total energy required for partial ablation was 225 +/- 91 J. The increase in PR (p less than 0.0001) and AH (p less than 0.001) intervals was proportional to the energy delivered. After ablation, the PR interval increased from 98 +/- 10 to 154 +/- 33 ms (p less than 0.004) and the AH interval from 59 +/- 8 to 102 +/- 16 ms (p less than 0.004). There was no significant change in QRS, QTc, HV or RR intervals. AH and PR intervals were significantly prolonged at 3, 7 and 14 days after ablation (p less than 0.05). Anterograde conduction was significantly altered in 10 dogs. Anterograde AV node effective refractory period increased from 157 +/- 14 to 214 +/- 45 ms (p less than 0.005). Anterograde AV node Wenckebach cycle length increased from 196 +/- 30 to 244 +/- 44 ms (p less than 0.002). Retrograde conduction was assessed in three dogs. Retrograde AV node effective refractory period increased from 156 +/- 21 to 260 ms in two dogs, with complete retrograde block in the third. These changes persisted for up to 2 weeks. Pathologic changes were limited to the region of the AV node. In four dogs adherent thrombus without pulmonary emboli was noted. Partial focal injury to the AV node is feasible in the canine model.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Nonpharmacological therapy of supraventricular arrhythmias: surgery and catheter ablation techniques.

Treatment of supraventricular tachyarrhythmias has undergone substantial change and development over the past decade. Pharmacological approaches to management of supraventricular arrhythmias have been supplanted by nonpharmacological techniques. These nonpharmacological techniques are the subject of the present review. The first part of this review will concentrate on the nonpharmacological techniques available for the treatment of supraventricular tachycardia, excluding Wolff-Parkinson-White syndrome, whereas Part 2 will concentrate on the surgical and the ablative procedures for management of tachycardias associated with Wolff-Parkinson-White syndrome. Pacing techniques for termination of supraventricular tachycardias are beyond the scope of this article and will not be included in the discussion.

Animals↗
PubMed1989

Treatment of malignant ventricular arrhythmias with the automatic implantable cardioverter defibrillator.

Twenty-eight patients with malignant ventricular arrhythmias were treated with the automatic implantable cardioverter-defibrillator (AICD) in a 14-month period. Thirteen patients were resuscitated from a ventricular fibrillation (VF) episode. Fifteen patients presented with ventricular tachycardia (VT) refractory to medical therapy. The etiology was coronary artery disease in 23 of 28 patients (82%), dilated cardiomyopathy in 2 of 28 patients (7%), sarcoidosis in 2 of 28 patients, and 1 patient in 28 had lupus erythmatosis. The mean left ventricular ejection fraction was 29%. A total of 27 of 28 patients (96%) patients had inducible ventricular tachycardia using programmed stimulation. The patients considered for AICD implant failed a mean of 3.6 antiarrhythmic drugs. Rate counting and defibrillating leads were inserted through a lateral thoracotomy in 17 patients and a mediansternotomy incision in 11 patients in conjunction with another cardiac procedure in 10 patients. The generators were positioned in a subcutaneous pocket beneath the left costal margin. There were no operative deaths. The mean follow-up was 6.7 months (range 1 to 14) with no VT/VF deaths in patients with defibrillators. The study demonstrated that AICD is an effective device for prevention of sudden cardiac death.

Adult↗
PubMed1989

Initial clinical experience with a rate responsive pacemaker.

Prism-CLR is a new single chamber unipolar pace, bipolar or unipolar sense, rate responsive pacemaker that utilizes a closed-loop system based on the analysis of the evoked potential for rate adjustment. It also has an automatic output regulation feature for capture verification and threshold search. Five patients in whom this pacemaker was implanted exhibited an appropriate rate increase with exercise and psychological stress. Automatic output regulation functioned appropriately in three of five patients. Preliminary data suggest that Prism-ClR is an effective pacemaker for patients who may benefit from rate responsive pacing. The automatic output regulation recognition algorithm may need modification in some patients.

Aged↗
PubMed1989

Alternating sequence of retrograde atrial activation in patients with dual AV nodal physiology.

Patients with dual AV nodal physiology have been demonstrated to have earliest retrograde activation sequence of the fast pathway in the lower septal right atrium and slow pathway in the proximal coronary sinus, and the posterior atrial septum. This case report describes a patient with dual AV nodal physiology demonstrating a dual sequence of retrograde activation with 2:1 block occurring in the fast pathway causing the conduction to proceed alternately via fast then slow pathway. This sequence was abolished by atropine allowing conduction to proceed via fast pathway. Surgical cure of patients with reentrant AV nodal tachycardia suggests the presence of two anatomically distinct AV nodal-like pathways. This case report confirms this observation and further suggests preferential autonomic modulation of the fast pathway.

Adult↗
PubMed1988

Implanted automatic defibrillators: effects of drugs and pacemakers.

The automatic implantable cardioverter defibrillator is an effective device for prevention of sudden cardiac death. Patients who require the implantation of the device often require permanent pacing for symptomatic bradyarrhythmias and may require antiarrhythmic drug therapy. Antiarrhythmic drugs may alter the defibrillation thresholds, arrhythmia cycle length and frequency, pacing thresholds and postshock excitability. Interactions between the defibrillator and the pacemaker may result in sensing problems, leading to multiple counting and inappropriate shocks, or ventricular fibrillation nondetection, sensing or capture failure post defibrillation and pacemaker reprogramming induced by defibrillator discharge. The potential for interactions will increase as the new generation of programmable defibrillators become clinically available, combining features of permanent pacemakers, antitachycardia pacemakers and defibrillators.

Anti-Arrhythmia Agents↗