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Biomedical subjects

C Halperin

Publications and source records attributed to C Halperin.

9 recordsLinked to original sources
PubMed1995

[Adequacy of of pacemakers responsive to the volume-minute ventilation rate in heart transplantation patients].

PURPOSE: To evaluate in the late post-operative period (PO) the chronotropic response to exercise of patients submitted to orthotopic cardiac transplantation (CT) and the implant of a cardiac pacemaker (PM). METHODS: A rate response ventricular PM (VVI+R) which uses minute ventilation (MV) as a sensor was implanted in five patients in the early PO of CT due to chronotropic incompetence. The patients were 31 to 64 years old and the indication to implant of PM was low ventricular escape rhythm following atrial taquicardia/bradycardia (one case) or sinus bradycardia (4 cases). The study was performed by means of paired exercise tests using Naughton protocol in order to compare the heart rate in VVI (prefixed heart rate) and VVIR+MV (rate response) mode. The duration of the exercise was compared between the two modes of stimulation. RESULTS: In VVI mode the heart rate was significantly lower than in VVIR+MV mode for comparable periods of exercise (101 +/- 12 ppm vs 132 +/- 4 ppm; p < 0.05); in VVIR+MV mode the patients had a prolonged time of exercise as compared to VVI mode (15 +/- 7 min vs 12 +/- 7 min; NS). CONCLUSION: The MV rate response PM provided patients with satisfactory heart during exercise and may be an adequate option to patients submitted to CT who present chronotropic incompetence.

Adult↗
PubMed1991

[Use of implantable pacemaker in the treatment of paroxysmal supraventricular tachycardia refractory to pharmacologic therapy].

PURPOSE: To evaluate the results with the use of an automatic antitachycardia pacemaker in patients with refractory paroxysmal supraventricular tachycardia. PATIENTS AND METHODS: Nine patients aged 32 to 63 years with symptoms from 2 to more than 40 years and prophylactic treatment with several antiarrhythmic drugs that had failed to control tachycardia. The frequency of attacks in the year before the implant was from 1 per month to 3 daily and 4 of patients required direct counter current cardioversion at least once. The electrophysiologic studies demonstrated atrioventricular (AV) nodal reentry in 6 and AV reentry utilizing an accessory AV connection in 4 patients (in one patient both mechanisms were present). The patients have been followed from 2 to 18 months. RESULTS: All patients experienced new episodes of the arrhythmia that were successfully terminated by the pacemaker. Two patients presented episodes of tachycardia not terminated by the pacemaker. These events were successfully treated by reprogramming the unit. The drug treatment was discontinued in 7 patients. CONCLUSION: The antitachycardia pacemaker proved to be an effective therapeutic tool in reentrant supraventricular tachycardia refractory to pharmacologic therapy.

Adult↗
PubMed1989

An unusual receptor mediates adenosine-induced SA nodal bradycardia in dogs.

To characterize the receptor mediating the negative chronotropic effect of adenosine in dogs, experiments were performed on conscious dogs with chronically implanted cardiovascular instrumentation. Autonomic blockade was used to eliminate any reflex influences on heart rate. Intravenous bolus injections of various adenosine analogues caused dose-dependent, aminophylline-blockable reductions in heart rate with a potency order of 5'-(N-ethylcarboxyamido)-adenosine (NECA)-78:2-chloroadenosine-17:adenosine-1. Dipyridamole enhanced the potency of adenosine to equal that of 2-chloroadenosine. Moderately selective A1-receptor agonists N6-(L-2-phenylisopropyl)-adenosine (R-PIA) and N6-cyclohexyladenosine and an A2-selective agonist 2-phenylaminoadenosine (200 nmol/kg) had no negative chronotropic effect in the conscious dog. Adenosine and its analogues, including R-PIA, caused coronary vasodilatation at smaller doses than were required to slow the heart rate. The selective A1-adenosine receptor blocker xanthine amine congener (XAC) antagonized the negative chronotropic action of adenosine but did so nonselectively, as the coronary vasodilative and negative chronotropic actions of adenosine were antagonized equally well. The spontaneous contraction rate of isolated perfused dog right atrial preparations, which included the sinoatrial node, was reduced by intrasinoatrial node artery infusions of adenosine analogues with a potency ratio of NECA-100:adenosine-15:N6-cyclopentyladenosine-2.3:R-PIA-1. We conclude that the adenosine receptor mediating the negative chronotropic action of adenosine in the dog does not display the pharmacological characteristics of either typical A1- or A2-adenosine receptors. Instead, either a novel adenosine receptor or an A1-receptor with unusual agonist and antagonist binding properties appears to exist in the dog's sinoatrial node.

2-Chloroadenosine↗