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G N Gupta

Publications and source records attributed to G N Gupta.

6 recordsLinked to original sources
PubMed1999

The creation of linear contiguous lesions in the atria with an expandable loop catheter.

OBJECTIVES: This article describes a catheter system designed to create linear atrial lesions and identifies electrophysiologic markers that are associated with the creation of linear lesions. BACKGROUND: Atrial fibrillation (Afib) is the most common arrhythmia in humans and causes a significant morbidity. The success of surgical interventions has provided the impetus for the development of a catheter-based approach for the ablation of Afib. METHODS: We tested a catheter system with 24 4-mm ring electrodes that can create loops in the atria. The electrodes can be used to record electrical activity and deliver radiofrequency power for ablation. In 33 dogs, 82 linear lesions were generated using three power titration protocols: fixed levels, manual titration guided by local electrogram activity and temperature control. Bipolar activity was recorded from the 24 electrodes before, during and after lesion generation. Data were gathered regarding lesion contiguity, transmurality and dimensions; the changes in local electrical activity amplitude; the incidence rate of rapid impedance rises and desiccation or char formation; and rhythm outcomes. RESULTS: Catheter deployment usually requires <60 s. Linear lesions (12 to 16 cm in length and 6 +/- 2 mm wide) can be generated in 24 to 48 min without moving the catheter. Effective lesion formation can be predicted by a decrease of greater than 50% in the amplitude of bipolar recordings. Splitting or fragmentation of the electrogram and increasing pacing threshold (3.1 +/- 3.3 mV to 7.1 +/- 3.8 mV, p < 0.01) are indicative of effective lesion formation. Impedance rises and char formation occurred at 91 +/- 12 degrees C. Linear lesion creation does not result in the initiation of Afib. However, atrial flutter was recorded after the completion of the final lesion in 3/12 hearts. When using temperature control, no char was noted in the left atrium, whereas 8% of the right atrium burns had char. CONCLUSIONS: This adjustable loop catheter forces the atrial tissue to conform around the catheter and is capable of producing linear, contiguous lesions up to 16 cm long with minimal effort and radiation exposure. Pacing thresholds and electrogram amplitude and character are markers of effective lesion formation. Although Afib could not be induced after lesion set completion, sustained atrial flutter could be induced in 25% of the hearts.

Animals↗
PubMed1984

Subcutaneous bioabsorbable pellets of norethindrone for contraception in women: Phase I. Clinical study.

Ten healthy, normally menstruating female volunteers participated in a 1-year phase I clinical study in which subcutaneous pellet implants of norethindrone (NET) were employed as a low-dose and long-acting potential contraceptive. Two NET pellets were implanted subcutaneously by the aid of a trocar in the forearm of each volunteer on the fifth day after the start of menstrual bleeding. Serum levels of NET, follicle-stimulating hormone, luteinizing hormone, 17 beta-estradiol, and progesterone were determined weekly by radioimmunoassay. The daily NET release from the pellets, based on mean values (+/- standard error of the mean) in five subjects was 79.4 +/- 7.6 micrograms. The mean serum NET level was initially 1.0 +/- 0.34 ng/ml; thereafter, it gradually lowered during the 343 days of the study period to the level of 0.43 +/- 0.09 ng/ml. The ovarian response, days of bleeding, and cycle lengths with continuously sustained release of NET from the pellets were similar to those observed in women taking the daily oral "minipill" of 300 micrograms NET. The results of the phase I study suggest that NET pellet implants may provide a simple and acceptable approach to long-term contraception in women.

Absorption↗
PubMed1980

Release of norethisterone from a bioabsorbable implant in female bonnet monkeys (Macaca radiata).

Bioabsorbable implants prepared by fusion of 85% norethisterone (NET) and 15% cholesterol were inserted subdermally in four cycling bonnet monkeys (Macaca radiata). No skin reaction or inflammation was observed at the site of implantation. Plasma concentration of norethisterone (NET) measured by radioimmunoassay were monitored for 14 to 16 months at monthly intervals. In the first month weekly samples were analysed. NET was released into circulation within 24 hours after insertion of the implant. In all the monkeys, except one, a sharp rise in NET (1.9 to 20 ng/ml) occurred immediately after insertion. Levels then remained between 1.7 and 0.6 ng/ml for about 4 months. Thereafter they remained steady up to about 9 months in two monkeys and gradually declined to about 0.4 ng/ml in the remaining two. In all except one, there was a sudden burst of NET release between the 10th and 11th month. The hormone almost cleared out of circulation by the 14th to 16th month. Initial menstrual cycles after pellet insertion were disturbed, leading to spotting and irregular bleeding. Regular cycles appeared from 5 to 8 months after the insertion of the implant. These cycles were ovulatory, as determined by the progesterone levels.

Animals↗
PubMed1979

Subdermal norethindrone pellets -- a method for contraception?

The mode of action of compressed pellets containing 85 per cent norethindrone (NET) and 15 per cent cholesterol was studied. Four pellets were inserted subcutaneously, in each of five healthy volunteers and left in place for 200--229 days. The NET content of the pellets varied between 23.9 mg and 25.6 mg; and the cholesterol content between 4.2 mg and 4.5 mg. Plasma levels of NET, estradiol and progesterone were determined by radioimmunoassays. Plasma levels of NET varied mostly between 1--2 ng/ml the first month after insertion. After two months plasma levels of NET ranged between 0.5 ng/ml and 1 ng/ml in all volunteers and there was a gradual decrease of the plasma NET levels throughout treatment. Pronounced day-to-day variations in plasma NET levels were recorded. The release rates of NET was calculated to be between 187 micrograms/day and 243 micrograms/day among the five volunteers. Ovulations occurred in four out of five subjects during treatment. This study indicates that the release of gestagen from four NET pellets was only initially high enough to completely inhibit ovulation and that to accomplish full contraceptive efficacy, a higher dose, i.e. more pellets, would have to be inserted.

Adult↗