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Biomedical subjects

R Mehra

Publications and source records attributed to R Mehra.

At least 37 records · Page 2Linked to original sources
PubMed1999

Evaluation of right atrial and biatrial temporary pacing for the prevention of atrial fibrillation after coronary artery bypass surgery.

OBJECTIVES: The purpose of this study was to determine if atrial pacing is effective in reducing postoperative atrial fibrillation (AF). BACKGROUND: Atrial fibrillation after coronary artery bypass grafting (CABG) is a common problem for which medical management has been disappointing. Atrial-based pacing has become an attractive nonpharmacologic therapy for the prevention of AF. METHODS: Sixty-one post-CABG patients (mean age = 65 years) were randomized to one of three groups: no atrial pacing (NAP), right atrial pacing (RAP) or biatrial pacing (BAP). Each patient had one set of atrial wires attached to both the right and left atria, respectively, at the conclusion of surgery. Patients in the RAP and BAP groups were continuously paced at a rate of 100 pulses per minute for 96 h or until the onset of sustained AF (>10 min). All patients were monitored with Holter monitors or full disclosure telemetry to identify the onset of AF. The primary end point of the study was the first onset of sustained AF. RESULTS: There was no significant difference in the proportion of patients developing AF in the three groups (NAP = 33%; RAP = 29%; BAP = 37%; p > 0.7). However, for the subset of patients on beta-adrenergic blocking agents after CABG, there was a trend toward less AF in the paced groups. There were no serious complications related to pacing, although in three patients the pacemaker appeared to induce AF by pacing during atrial repolarization. CONCLUSIONS: Continuous right or biatrial pacing in the postoperative setting is safe and well tolerated. We did not find that post-CABG pacing prevented AF in this pilot study; however, the role of combined pacing and beta-blockade merits further study.

Adolescent↗
PubMed1999

Thiotepa, busulfan and cyclophosphamide as a preparative regimen for allogeneic transplantation for advanced chronic myelogenous leukemia.

Thirty-six adults with chronic myelogenous leukemia (CML) in second or greater chronic phase, accelerated phase, or blast crisis underwent marrow or blood stem cell transplantation from an HLA-matched sibling using high-dose thiotepa, busulfan and cyclophosphamide (TBC) as the preparative regimen. All evaluable patients engrafted and had complete donor chimerism. One patient failed to clear meningeal leukemia, and one patient had one of 30 metaphases positive for the Philadelphia chromosome at 2 months post transplant. The remainder of the patients studied had eradication of CML documented by cytogenetics and/or Southern blot for BCR gene rearrangement, and 13 of 15 patients studied became negative for the BCR gene rearrangement by polymerase chain reaction. Three-year relapse rate is 42% (95% CI, 19-64%). The relapse rate was significantly lower for patients transplanted without blast crisis (9% vs 100%, P < 0.001). Eight (22%, 95% CI, 10-39%) patients had severe or fatal veno-occlusive disease (VOD). Elevated liver enzymes within 1 month prior to transplantation and transplantation using marrow were significantly associated with the occurrence of VOD. Three-year survival is 28% (95% CI, 13-43%). Survival was significantly higher for patients transplanted without blast crisis (45% vs 0%, P = 0.01). TBC is an effective preparative regimen for CML in accelerated phase but not refractory blast crisis, and it should be used with caution in patients with prior hepatopathy who have an increased risk of severe VOD.

Adult↗
PubMed1999

Tacrolimus and minidose methotrexate for prevention of acute graft-versus-host disease after HLA-mismatched marrow or blood stem cell transplantation.

Thirty adults with leukemia or lymphoma transplanted with marrow or blood stem cells from 1-antigen mismatched related donors received tacrolimus and minidose methotrexate to prevent acute graft-versus-host disease (GVHD). The group had a median age of 42 years (range 18-56 years). Twenty-seven patients had advanced disease, and 13 were resistant to conventional therapy. Tacrolimus was administered at 0.03 mg/kg/day i.v. by continuous infusion from day -2, converted to oral at four times the i.v. dose following engraftment, and continued to day 180 post-transplant. Methotrexate 5 mg/m2 was given i.v. on days 1, 3, 6 and 11. Mild nephrotoxicity was common before day 100; 69% of patients had a doubling of creatinine, 56% had a peak creatinine greater than 2 mg/dl, and two patients were dialyzed. Other toxicities prior to day 100 thought to be related to tacrolimus included hypertension (45%), hyperkalemia (17%), hyperglycemia (14%), seizures (13%), headache (3%) and hemolytic uremic syndrome (3%). Grades 2-4 GVHD occurred in 59% (95% CI, 38-70%), and grades 3-4 GVHD in 17% (95% CI, 1-32%). Overall survival at 1 year was 29% (95% CI, 12-45%). We conclude that tacrolimus and minidose methotrexate is active post-transplant immunosuppression for patients with 1-antigen mismatched donors.

Acute Disease↗
PubMed1999

Carmustine, etoposide, cytarabine and melphalan as a preparative regimen for allogeneic transplantation for high-risk malignant lymphoma.

BACKGROUND: The combination of carmustine, etoposide, cytarabine and melphalan (BEAM) is an effective autologous transplantation preparative regimen for lymphoma and has little toxicity, but the feasibility and tolerance of BEAM as a preparative regimen for allogeneic transplantation has not been established. PATIENTS AND METHODS: Thirty adults with primary refractory or recurrent intermediate- or low-grade lymphoma were treated on a prospective phase II study with carmustine 300 mg/m2 i.v. day -6, etoposide 200 mg/m2 i.v. followed by cytarabine 200 mg/m2 i.v. twice daily days -5 to -2, melphalan 140 mg/m2 i.v. day -1, and marrow or blood stem cells from an HLA-identical donor on day 0. Tacrolimus and methotrexate were used to prevent graft-vs.-host disease (GVHD). RESULTS: Median time from transplantation was 20 mos (range 6-32 months). Median maximal regimen-related toxicity grade was 2, and four patients (13%) had a grade 3-4 regimen-related toxicity. Two patients had idiopathic interstitial pneumonitis. One patient had primary graft failure, and a second had autologous reconstitution documented at three months posttransplant. Grades 2-4 acute GVHD occurred in 31%, grades 3-4 in 16%, and chronic GVHD in 54%. Day-100 survival was 70%. Twenty-three patients achieved a complete response. The two-year relapse rate was 23%, survival was 48%, and disease-free survival (DFS) was 42%. CONCLUSIONS: BEAM supports engraftment of allogeneic transplants and is a tolerable preparative regimen for allogeneic transplantation for lymphoma.

Adult↗
PubMed1998

Finite element analysis of defibrillation fields in a human torso model for ventricular defibrillation.

In order to optimize defibrillation electrode systems for ventricular defibrillation thresholds (DFTs), a Finite Element Torso model was built from fast CT scans of a patient who had large cardiac dimensions (upper bound of normal) but no heart disease. Clinically used defibrillation electrode configurations, i.e. Superior Vena Cava (SVC) to Right Ventricle (RV) (SVC-RV), left pectoral Can to RV (Can-RV) and Can + SVC-RV, were analyzed. The DFTs were calculated based on 95% ventricular mass having voltage gradient > 5 V/cm and these results were also compared with clinical data. The low voltage gradient regions with voltage gradient < 5 V/cm were identified and the effect of electrode dimension and location on DFTs were also investigated for each system. A good correlation between the model results and the clinical data supports the use of Finite Element Analysis of a human torso model for optimization of defibrillation electrode systems. This correlation also indicates that the critical mass hypothesis is the primary mechanism of defibrillation. Both the FEA results and the clinical data show that Can + SVC-RV system offers the lowest voltage DFTs when compared with SVC-RV and Can-RV systems. Analysis of the effect of RV, SVC and Can electrode dimensions and locations can have an important impact on defibrillation lead designs.

Computational Biology↗
PubMed1998

Effect of altering the daily herbage allowance to cows in mid lactation on the composition, ripening and functionality of low-moisture, part-skim Mozzarella cheese.

Milk was collected from three spring-calving herds, on different daily herbage allowances (DHA) of perennial rye-grass (16, 20 or 24 kg dry matter (DM)/cow for a 17 week period. On five occasions, at weekly intervals in the middle of the period, the three different milks were converted into low-moisture part-skim Mozzarella cheese. Increasing the DHA resulted in significant increases in the concentrations of protein in the cheesemilk (P < 0.05) and cheese whey (P < 0.02). The moisture-adjusted cheese yield increased significantly (P < 0.01) on raising the DHA from 16 to 24 kg grass DM/cow. DHA had no significant effects on any of the gross compositional values of the cheese (although moisture and fat-in-DM levels tended to decrease and increase respectively with increasing DHA). The hardness of the uncooked cheese and functionality of cooked cheese (i.e. melt time, flowability, stretch and viscosity) were not significantly influenced by DHA over the 115 d ripening period at 4 degrees C.

Animals↗
PubMed1998

Design and implementation of the Dual Site Atrial Pacing to Prevent Atrial Fibrillation (DAPPAF) clinical trial. DAPPAF Phase 1 Investigators.

The Dual Site Atrial Pacing to Prevent Atrial Fibrillation (DAPPAF) study compares dual site, single site and support pacing modalities in the prevention of atrial fibrillation (AF) in patients with a history of paroxysmal AF (PAF) and a bradyarrhythmic indication for pacing. The trial is a randomized crossover comparison of dual site atrial pacing, single site atrial pacing, and a support pacing control period (DDI at 50 ppm or VDI) done in six month intervals. Patient inclusion requires at least 2 documented AF episodes in the three months prior to enrollment. The patients can be on concurrent antiarrhythmic drug regimens but this regimen must remain constant throughout the protocol. Patients with AV nodal ablation are excluded from this study. The primary endpoints of the study compare the time to first recurrence of clinically significant symptomatic AF with ECG verification, and quality of life among the three treatment modes. Secondary endpoints include time to first recurrence of all AF episodes as monitored by the pacemaker, the measurement of echocardiographic parameters, and symptoms logged by the patients. This trial was designed after pilot studies showed dual site pacing to be safe, feasible and preliminary results suggested increased maintenance of sinus rhythm with atrial pacing.

Adult↗
PubMed1998

Comparison of standard and irrigated radiofrequency ablation in the canine ventricle.

INTRODUCTION: Radiofrequency ablation is successful for treating some arrhythmias but not for CAD-VT, possibly due to insufficient lesion size. Irrigated electrodes were developed to apply higher power for longer duration to create larger lesions. Our objective was to characterize and compare irrigated and standard ablation in terms of lesion size, crater, and coagulum formation. Additionally, a method is proposed for creating large irrigated lesions without craters. METHODS AND RESULTS: Three ablation protocols were conducted in canine ventricles. Protocol I: standard ablation was performed in power mode at 10, 20, 30, and 50 W, and electrode-temperature mode at 70 degrees and 90 degrees C (120 sec). Protocol II: irrigated ablation was conducted with 30 and 50 W (30 and 120 sec). Protocol III: to create large lesions without craters, irrigated ablation was performed at 20 W (5 and 10 min). With a standard electrode, the largest lesions were created using 20 W (358+/-194 mm3) and using 90 degrees C (301+/-130 mm3). Ablation duration decreased with power for the power mode standard ablations. The largest irrigated lesions were formed using 50 W (986+/-357 mm3). Large lesions without craters were created with irrigation using 20 W for 10 minutes (602+/-175 mm3). Coagulum was seen for most standard ablations but infrequently for irrigated ablations. Craters were observed with 30 and 50 W irrigated ablation but were not observed with 20 W irrigated ablation. CONCLUSION: Irrigated ablation created larger lesions than standard; large lesions may be created without craters using moderate power and long duration.

Animals↗
PubMed1998

Lead fixation in dogs achieved with RF energy.

INTRODUCTION: The purpose of this study was to test whether radiofrequency (RF) energy could be used to fixate leads to the endocardium. METHODS AND RESULTS: In six dogs we measured the dislodgment force and pacing threshold before and after RF fixation in the coronary sinus (CS) and right ventricle (RV). RF fixation was achieved with a CardioRhythm Atakr ablation unit. The dislodgment force of CS leads fixed with RF energy was 1.63+/-0.65 oz, compared with < 0.1 oz for similar leads placed in the CS of six separate dogs. In the RV, leads fixed with RF energy had a dislodgment force of 1.29+/-0.27 oz, compared with 0.48+/-0.28 oz. for urethane (P < 0.01) and 1.01+/-0.21 oz for silicone (P = 0.41) tined leads. In the CS, the pacing threshold for RF fixed leads increased significantly from 2.2+/-1.1 V (0.5 msec) before fixation to 4.2+/-1.3 V after fixation (P < 0.01), while in the RV, the pacing threshold increased from 0.41+/-0.05 V (0.5 msec) before fixation to a mean of 2.03+/-0.44 V after fixation (P < 0.01). In another group of six dogs studied for 12 weeks, 5 of 6 RF fixed CS leads remained attached, as did 8 of 10 RF fixed RV leads. For the RV leads, the mean pacing threshold was 0.90+/-0.35 V, compared with 0.53+/-0.18 V (0.5 msec) for similar tined leads (P = 0.02) and 1.2+/-0.30 V (0.5 msec) for screw leads (P = 0.18) in the RV. CONCLUSION: We conclude that RF energy can be used to attach leads to the RV and CS endocardium. While the RV pacing thresholds increased acutely, the mean chronic thresholds were not significantly different for RF fixed leads and standard tined or screw leads.

Animals↗
PubMed1998

High-dose chemotherapy for relapsed and refractory diffuse large B-cell lymphoma: mediastinal localization predicts for a favorable outcome.

PURPOSE: This study was performed to evaluate the outcome of high-dose chemotherapy and autologous transplantation in patients with diffuse B-cell large-cell lymphoma, and, specifically, to evaluate the impact of primary mediastinal localization on the outcome of high-dose chemotherapy. PATIENTS AND METHODS: A retrospective review was performed of all patients with diffuse large B-cell lymphoma who underwent autologous marrow or peripheral-blood stem-cell transplantation at our institution between January 1 986 and December 1995. RESULTS: Ninety patients were identified, of whom 31 (34%) had a primary mediastinal B-cell large-cell lymphoma (PML). Cumulative probabilities of disease-free survival, overall survival, and disease progression are 40% (95% confidence interval [CI], 29 to 51), 42% (95% CI, 31 to 53), and 52% (95% CI, 40 to 64), respectively. By univariate analysis, low lactate dehydrogenase (LDH) level and low Ann Arbor stage at transplant were associated with improved survival and disease-free survival. There was a trend for improved disease-free survival and survival for patients with PML. Multivariate stepwise Cox regression analysis showed that LDH level, Ann Arbor stage, and primary mediastinal localization were independent favorable prognostic factors for disease-free survival and survival. LDH level and Ann Arbor stage were also predictive for the risk of disease progression. CONCLUSION: Our results indicate that patients with PML may display an increased susceptibility to high-dose chemotherapy compared with other types of B-cell large-cell lymphoma. These findings, if confirmed, may have implications for the initial management of patients with PML.

Adolescent↗
PubMed1998

Chemotherapy immediately following autologous stem-cell transplantation in patients with advanced breast cancer.

Most patients relapse after high-dose chemotherapy (HDCT) with autologous stem-cell transplantation (ASCT) for metastatic breast cancer. Further chemotherapy immediately after hematopoietic recovery from ASCT is not given for fear of irreversibly damaging the newly engrafted stem cells. In a pilot chemoprotection trial, autologous CD34+ cells from patients with metastatic breast cancer were exposed to a replication-incompetent retroviral vector carrying MDR-1 cDNA and then reinfused after HDCT. Immediately on recovery, patients received multiple courses of escalating dose paclitaxel. All of the 10 patients tolerated reinfusion of modified cells without any toxicity and had myeloid engraftment within 12 days (range, 11-14). The bone marrow cells of three patients contained vector MDR-1-positive cells only at the time of the first course of posttransplant paclitaxel, indicating that the MDR-1 vector-modified cells had only short-term engrafting potential. A total of 83 courses of paclitaxel were administered starting at a median of 30 (range, 21-32) days from ASCT. The median dose of paclitaxel was 225 mg/m2 and the median interval between paclitaxel cycles of therapy was 21 (range, 20-41) days. Five of the six CR patients were able to receive all of the 12 courses of paclitaxel. Three patients who had achieved less than a complete response to the HDCT (2 patients) and partial response (1 patient) were converted to complete clinical responses during the 12 cycles of paclitaxel. No delayed toxicity or bone marrow failure was noted in these patients with a median follow-up of 2 years from ASCT. This is the first study of chemotherapy immediately after transplantation with autologous CD34+ cells. These data indicate that paclitaxel can be safely administered immediately after ASCT without any delayed toxicities. Paclitaxel given immediately after ASCT can further improve the response to pretransplant chemotherapy in patients with advanced breast cancer.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Low-energy endocardial defibrillation using dual, triple, and quadruple electrode systems.

The feasibility of achieving both universal application of nonthoracotomy leads and low (< or = 15 J) defibrillation energy requirements by optimizing lead system configuration for use with low-output (<30 J) biphasic shock pulse generators was examined. Sixteen patients (mean age 62 +/- 8 years and mean left ventricular ejection fraction of 38 +/- 15%) were included in the study. All patients had either experienced syncope with induced ventricular tachycardia (n = 4) or had documented sustained ventricular tachycardia (n = 7) or ventricular fibrillation (n = 5). Defibrillation threshold testing was performed in 2 stages on different days in these patients. In the first stage, 2 defibrillation catheter electrodes were positioned in the right ventricle and superior vena cava with an axillary cutaneous patch. Fifteen-joule, 10- and 5-J biphasic shocks were delivered across 3 different electrode configurations-right ventricle to superior vena cava, right ventricle to axillary patch, right ventricle to a combination of superior vena cava and axillary patch. In the second stage, an 80-ml can electrode was added subcutaneously in a pectoral location to the previous leads. Configurations compared were the right ventricle to pectoral can, and right ventricle to an "array"-combining superior vena cava, can, and axillary patch leads. The defibrillation threshold was determined using a step-down method. In stage 1, mean defibrillation threshold for the right ventricle to axillary patch (12.7 +/- 5.9 J) and right ventricle to superior vena cava plus axillary patch (9.8 +/- 5.2 J) configurations was lower than the right ventricle to superior vena cava configuration (14.2 +/- 6.4 J, p <0.05). In stage 2, the defibrillation was higher for the right ventricle to pectoral can (9.2 +/- 5.1 J) configuration compared with the right ventricle to the array (5.6 +/- 3.6 J, p < or =0.05). The right ventricle to array had the lowest defibrillation threshold, whereas the right ventricle to pectoral can was the best dual electrode system. Low-energy endocardial defibrillation (< or =10 J) was feasible in 72% of tested patients with > 1 electrode configuration at 10 J, whereas only 53% of successful patients could be reverted at >1 electrode configuration at 5 J (p <0.05). Reduction in maximum pulse generator output to < or =25 J using these electrode configurations with bidirectional shocks is feasible and maintains an adequate safety margin.

Aged↗
PubMed1997

Engraftment of allogeneic hematopoietic progenitor cells with purine analog-containing chemotherapy: harnessing graft-versus-leukemia without myeloablative therapy.

The immune-mediated graft-versus-leukemia effect is important to prevent relapse after allogeneic progenitor cell transplantation. This process requires engraftment of donor immuno-competent cells. The objective of this study was to assess the feasibility of achieving engraftment of allogeneic peripheral blood or bone marrow progenitor cell after purine analog containing nonmyeloablative chemotherapy. Patients with advanced leukemia or myelodysplastic syndromes (MDS) who were not candidates for a conventional myeloablative therapy because of older age or organ dysfunction were eligible. All patients had an HLA-identical or one-antigen-mismatched related donor. Fifteen patients were treated (13 with acute myeloid leukemia and 2 with MDS). The median age was 59 years (range, 27 to 71 years). Twelve patients were either refractory to therapy or beyond first relapse. Eight patients received fludarabine at 30 mg/m2/d for 4 days with idarubicin at 12 mg/m2/d for 3 days and ara-c at 2 g/m2/d for 4 days (n = 7) or melphalan at 140 mg/m2/d (n = 1). Seven patients received 2-chloro-deoxyadenosine at 12 mg/m2/d for 5 days and ara-C 1 at g/m2/d for 5 days. Thirteen patients received allogeneic peripheral blood stem cells and 1 received bone marrow after chemotherapy. Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine and methyl-prednisolone. Treatment was generally well tolerated, with only 1 death from multiorgan failure before receiving stem cells. Thirteen patients achieved a neutrophil count of greater than 0.5 x 10(9)/L a median of 10 days postinfusion (range, 8 to 17 days). Ten patients achieved platelet counts of 20 x 10(9)/L a median of 13 days after progenitor cell infusion (range, 7 to 78 days). Eight patients achieved complete remissions (bone marrow blasts were < 5% with neutrophil recovery and platelet transfusion independence) that lasted a median of 60 days posttransplantation (range, 34 to 170+ days). Acute GVHD grade > or = 2 occurred in 3 patients. Chimerism analysis of bone marrow cells in 6 of 8 patients achieving remission showed > or = 90% donor cells between 14 and 30 days postinfusion, and 3 of 4 patients remaining in remission between 60 and 90 days continued to have > or = 80% donor cells. We conclude that purine analog-containing nonmyeloablative regimens allow engraftment of HLA-compatible hematopoietic progenitor cells. This approach permits us to explore the graft-versus-leukemia effect without the toxicity of myeloablative therapy and warrants further study in patients with leukemia who are ineligible for conventional transplantation with myeloablative regimens either because of age or concurrent medical conditions.

Acute Disease↗
PubMed1997

Complete remission of refractory gestational trophoblastic disease with brain metastases treated with multicycle ifosfamide, carboplatin, and etoposide (ICE) and stem cell rescue.

Patients with chemotherapy-refractory gestational trophoblastic disease and brain metastasis are considered to have a very poor prognosis. We present the case of a patient who had failed several chemotherapeutic regimens. Despite transient responses to chemotherapy, she had not achieved a complete remission in 3 years, and had developed systemic disease and recurrent brain metastasis. She was treated with four cycles of high-dose ifosfamide, carboplatin, and etoposide with blood progenitor cell support. She tolerated this regimen well and has obtained a complete remission that is ongoing for 12 months.

Adult↗
PubMed1997

Acute effects of dual-site right atrial pacing in patients with spontaneous and inducible atrial flutter and fibrillation.

OBJECTIVES: We tested the ability of dual-site right atrial pacing to prevent atrial fibrillation (AF) or atrial flutter induced by single-site atrial pacing and correlated its efficacy with clinical patient characteristics, atrial activation times and refractory periods. BACKGROUND: Prevention of recurrent AF with long-term dual-site right atrial pacing has been demonstrated in our previous studies. However, the mechanism of antiarrhythmic benefit is unclear. METHODS: Using standard electrophysiologic methods, baseline electrocardiographic and electrophysiologic measurements (mean +/- SD) were obtained. Programmed atrial stimulation was performed for AF or atrial flutter induction. Atrial pacing was performed at two drive cycle lengths (600 and 400 ms) and followed by one to three atrial extrastimuli at one to four pacing sites in the right atrium. In patients with inducible AF or atrial flutter, reinduction was then attempted during a dual-site atrial pacing drive train. This was achieved by simultaneously pacing at the high right atrium and coronary sinus ostium at an identical rate to the baseline stimulation, with the atrial extrastimuli being delivered at the pacing site responsible for the initial AF episode initiation. RESULTS: Twenty patients (10 men, 10 women, mean [+/- SD] age 64 +/- 16 years) with symptomatic AF (n = 10) or atrial flutter (n = 10) were studied. There was a significant abbreviation of the P wave duration to 103 +/- 17 ms with dual-site pacing compared with sinus rhythm (120 +/- 12 ms, p = 0.005) and high right atrial pacing (121 +/- 17 ms, p = 0.005). This was also associated with a characteristic change in P wave configuration with an inferior and leftward axis shift. The effective refractory period at the high right atrium remained unchanged with dual-site atrial pacing compared with single-site high right atrial pacing. Sixteen patients had inducible AF or atrial flutter and could be tested after dual-site atrial pacing. The induced atrial tachyarrhythmia was suppressed in nine patients (56%), who had either induced AF (n = 5) or atrial flutter (n = 4). The difference in the effective refractory period between the high right atrium and the coronary sinus ostium pacing sites was significantly greater (33 +/- 12 ms) in patients with suppression of atrial tachyarrhythmia with dual-site atrial pacing compared with patients without suppression (15 +/- 13 ms, p = 0.001). P wave abbreviation did not correlate with arrhythmia suppression. There was no correlation between suppression of inducible AF or atrial flutter and demographic or clinical patient characteristics. CONCLUSIONS: Dual-site right atrial pacing from the high right atrium and coronary sinus ostium can suppress inducible AF or atrial flutter elicited after single-site high right atrial pacing in selected patients. Acute suppression is more likely in patients with greater dispersion of right atrial refractoriness between these two sites.

Adult↗
PubMed1997

Hormonal therapy increases arterial compliance in postmenopausal women.

OBJECTIVES: This study investigated the effects of hormonal therapy on large arterial properties. BACKGROUND: Arterial stiffness is an emerging risk marker for coronary heart disease and is potentially modifiable. Postmenopausal use of hormonal therapy is associated with a lower risk of coronary heart disease. METHODS: Total systemic arterial compliance (SAC) and pulse wave velocity (PWV) were determined in 26 premenopausal and 52 postmenopausal women, 26 of whom were taking hormonal therapy. RESULTS: Arterial compliance was greater in the premenopausal group (mean +/- SEM 0.57 +/- 0.04 arbitrary compliance units [ACU]) than in the postmenopausal group not taking hormonal therapy (0.26 +/- 0.02 ACU, p = 0.001). Postmenopausal women taking hormonal therapy had a significantly increased total SAC compared with women not taking hormonal therapy (0.43 +/- 0.02 vs. 0.26 +/- 0.02 ACU, p = 0.001). PWV in the aortofemoral region in the premenopausal women was 6.0 +/- 0.2 vs. 8.9 +/- 0.3 m/s (p < 0.001) in untreated postmenopausal women. However, postmenopausal women taking hormonal therapy had a significantly lower PWV than those not taking hormonal therapy (7.9 +/- 0.2 vs. 8.9 +/- 0.3 m/s, p = 0.01). Eleven postmenopausal women had their hormone replacement therapy withdrawn for 4 weeks, resulting in a significant decrease in SAC and a significant increase in aortofemoral PWV. CONCLUSIONS: The increased SAC and decreased PWV in women receiving hormonal therapy suggest that such therapy may decrease stiffness of the aorta and large arteries in postmenopausal women, with potential benefit for age-related cardiovascular disorders. The reduction of arterial compliance with age appears to be altered with hormonal therapy.

Adolescent↗
PubMed1997

Effects of high-frequency atrial pacing in atypical atrial flutter and atrial fibrillation.

Atypical atrial flutter has, hitherto, been relatively refractory to termination by rapid atrial pacing. High-frequency pacing (HFP) in the atrium, for termination of atrial flutter or atrial fibrillation (AF), and the electrophysiologic effects related to it have not been examined. We examined the clinical efficacy, safety, and electrophysiologic mechanisms of HFP using 50-Hz bursts at 10 mA applied at the high right atrium in patients with atypical atrial flutter (group 1) or AF (group 2), using a prospective randomized study protocol. Four burst durations (500, 1000, 2000, and 4000 ms) were applied at the high right atrium repetitively in random sequence in 22 patients with spontaneous atrial flutter or AF. Local and distant right and left atrial electrogram recordings were analyzed during and after HFP. HFP resulted in local and distant right and left atrial electrogram acceleration in 8 of 10 patients (80%) in group 1 but caused less frequent local atrial electrogram acceleration (6 of 12 patients) and no distant atrial electrogram effects in group 2 (p < .05 versus group 1). The HFP protocol was effective in arrhythmia termination in 6 of 10 patients in group 1 but in no patient in group 2 (p < .05 versus group 1). Standard HFP protocol applied at the high right atrium can frequently alter atrial activation in both atria and can terminate atypical atrial flutter. Efficacy in AF is limited, probably due to limited electrophysiologic actions beyond the local pacing site.

Adult↗