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Biomedical subjects

A S Tang

Publications and source records attributed to A S Tang.

At least 37 records · Page 2Linked to original sources
PubMed1997

Definition of life quality from a patient versus health care professional perspective.

Quality of life assessment is increasingly acknowledged as an important component in selecting optimal health interventions for persons with cardiovascular disease. We hypothesized that cardiac out-patients have the same perception of what comprises quality of life as do their health care providers. A list of items was compiled from all quality of life measures and quality of life research. Staff members, cardiac out-patients and family members were asked what they considered important to the patients' quality of life by rating the relative importance of each item on the list. The three groups differed in their ratings. Of the top ten items ranked by patients, only three items appeared on the staff top ten list, and five on the family member's list. The patients, in contrast with staff and family, chose aspects of QL that reflected the positive aspects of life. These differences were more marked in the physical, psychological, and activity domains than in the social domain. The study suggests that QL measures developed from the perspective of primary caregivers are probably invalid and therefore QL measures should be developed from a patients perspective.

Adult↗
PubMed1997

Correlation of the heart rate-minute ventilation relationship with clinical data: relevance to rate-adaptive pacing.

The heart rate (HR)-minute ventilation (VE) relationship has been shown to be nonlinear and can be expressed as two distinct straight lines. This study is to assess the correlation of the initial HR-VE slope to clinical parameters. Maximum treadmill exercise tests were performed in 100 healthy volunteers (age 19-77 years) using a ramp protocol in which work-rate increases linearly with exercise. Breath-by-breath VO2, VCO2, and VE were measured, and HR and BP were monitored throughout the exercise. The HR-VE curve demonstrated nonlinearity with a breakpoint determined by a change point analysis. This breakpoint was significantly higher than that of the anaerobic threshold. The VE at the HR-VE breakpoint was 56.4 +/- 19.4 and VE at the VE-VO2-VO2 breakpoints were 48.0 +/- 18.3 (P < 0.0001) and 40.1 +/- 16.5 (P < 0.0001), respectively. The HR at this HR-Ve breakpoint was 77.7 +/- 12.9% of the HR range. The first slope, S1 (1.76 +/- 0.64) was steeper than the second slope, S2 (0.66 +/- 0.39). Although there was a gender difference for S1, the best clinical predictor on a stepwise multiple regression analysis was body surface area (BSA) which explained 47% of the variance. It was concluded that nonlinearity of the HR-VE curve can be expressed as two straight lines. The breakpoint is beyond the anaerobic threshold and can be estimated to be approximately 75% of the maximal predicted HR. BSA is the only clinical parameter that significantly predicts the initial slope of the HR-VE curve. This can be of great importance in the programming of rate-adaptive pacemakers using a VE.

Adult↗
PubMed1997

Torsade de pointes with amiodarone in a patient with previous torsade during beta-receptor blockade.

Torsade de pointes is a potentially lethal ventricular arrhythmia that is associated with prolonged QT intervals and is often caused by drugs that prolong repolarization. Among the most common drugs that may cause torsade de pointes are antiarrhythmic drugs including quinidine, procainamide, sotalol and newer class III antiarrhythmic agents. The incidence of torsade de pointes associated with amiodarone, however, is reported to be much lower. A case is reported of amiodarone-induced torsade de pointes following the development of the same arrhythmia during beta-blocker use. This case illustrates that although the reported incidence of torsade de pointes during amiodarone therapy is low, patients with bradycardia-induced torsade de pointes may be a subgroup of patients who are at increased risk of this arrhythmia with amiodarone.

Adrenergic beta-Antagonists↗
PubMed1996

Class III antiarrhythmic effects of LY-190147 on defibrillation threshold.

Defibrillation strength shocks delivered within an action potential (AP) delay repolarization. Shock-induced AP duration extension (APDE) may prolong refractoriness and terminate or prevent reinitiation of reentry, favoring defibrillation. This study examined LY-190147 (LY) effects on defibrillation threshold (DFT) in 11 dogs. Ventricular effective refractory period (VERP) and epicardial monophasic AP duration at 75% repolarization (APD75) were recorded at 300-, 400-, 500-, and 600-ms pacing cycle length (CL). APDE was measured as the time to 50% repolarization after a DFT strength shock delivered at 50, 25, and 0 ms before or 25 ms after VERP during pacing at 300 ms CL in 4 of the dogs. We made all recordings before drug administration and after infusions of 0.03, 0.3, and 3.0 mg/kg LY, using 1.5-h dosing intervals. LY lowered DFT in a saturating dose-response manner whether expressed as shock peak voltage (V) or energy. LY decreased DFT-V from 357 +/- 77 V before drug to 331 +/- 60 V (-6 +/- 12%), 290 +/- 43 V (-17 +/- 13%, p < 0.001), and 312 +/- 45 V (-11 +/- 12%, p < 0.05) at 0.03, 0.3, and 3.0 mg/kg, respectively. Similarly, LY treatment decreased defibrillation energy requirements from 6.9 +/- 2.7 J before drug by 7 +/- 25%, 26 +/- 24%, and 12 +/- 25% at the same doses. At 300-600 ms CL, LY prolonged APD75 by an average of 10 +/- 8% at 0.03 mg/kg, 17 +/- 6% at 0.3 mg/kg, and 24 +/- 9% at 3 mg/kg. At these CL, LY prolonged VERP by an average of 4 +/- 6% at 0.03 mg/kg, 15 +/- 10% at 0.3 mg/kg, and 11 +/- 9% at 3 mg/kg. APDE was increased from 62 +/- 9 ms before to 68 +/- 14, 80 +/- 16 (p < 0.001) and 72 +/- 13 ms (p < 0.05) at 0.03, 0.3, and 3.0 mg/kg LY, respectively. Therefore, LY prolonged VERP and APDE and affected DFT in the same saturating dose-response manner. LY may facilitate defibrillation by increasing the duration of postshock refractoriness.

Action Potentials↗
PubMed1996

Nonthoracotomy implantation of cardioverter defibrillators: preliminary experience with a defibrillation lead placed at the right ventricular outflow tract.

UNLABELLED: Although morbidity and mortality associated with defibrillator implantation using a nonthoracotomy approach have decreased as compared with a thoracotomy approach, defibrillation thresholds have been higher and fewer patients satisfied implant criteria. It may be possible to improve on the success of nonthoracotomy defibrillator implantation by the placement of a right ventricular (RV) outflow defibrillation lead. Implantable cardioverter defibrillator implantation data of 30 consecutive patients with clinical VT or VF were reviewed. Three defibrillation leads were routinely used. When either pacing threshold at the RV apex was inadequate (n = 2) or 18-J shocks were not successful in terminating VF in 3 of 4 trials (n = 8), the RV apex lead was positioned to the RV outflow tract attaching to the septum. Defibrillation testing was first performed with the RV apex lead in combination with CS, SVC, and/or subcutaneous leads. Twenty patients satisfied implant criteria with a defibrillation threshold of 13.5 +/- 3.6 J. In 7 of the 10 patients, whose RV lead was repositioned to the RV outflow tract, this lead in combination with SVC, CS, or subcutaneous leads produced successful defibrillation at < or = 18 J or in 3 of 4 trials. This approach improved the overall success of nonthoracotomy implantation of defibrillators from 69% to 90%. After a follow-up of 27 +/- 6 months, there was no dislodgment of the RV outflow tract defibrillation leads. CONCLUSIONS: This article reports the preliminary observation that placement of defibrillation leads to the RV outflow tract in humans was possible and without dislodgment. RV outflow tract offers an alternative for placement of defibrillation leads, which may improve on the success of nonthoracotomy defibrillator implantation.

Adult↗
PubMed1996

Improvement of ventricular function after atrioventricular junction ablation in a patient with atrial flutter after Mustard's operation.

Arrhythmias are common problems following Mustard's operation for D-transposition of the great arteries. A 19-year-old male is presented who was diagnosed at birth with D-transposition of the great arteries and a right aortic arch and underwent a Mustard procedure at 12 months of age. He developed sinus node dysfunction and atrial flutter unresponsive to antiarrhythmic drugs and dual chamber pacing. Following complete heart block with radiofrequency catheter ablation of the atrioventricular junction, the patient's heart was paced in VVIR mode. Ventricular function improved after the ablation and persisted in two years' follow-up.

Adult↗
PubMed1995

Comparison of monophasic and biphasic defibrillating pulse waveforms for transthoracic cardioversion. Biphasic Waveform Defibrillation Investigators.

All transthoracic defibrillators on the US market use nominally monophasic shock waveforms. However, biphasic waveforms have a lower defibrillation threshold than monophasic waveforms for transthoracic defibrillation of animals and for defibrillation of humans by implantable cardioverter defibrillators. The relative efficacies of Edmark monophasic and Gurvich biphasic transthoracic cardioversion waveforms (200 J into 50 omega) were compared for transthoracic cardioversion in 171 patients undergoing electrophysiologic study for evaluation of ventricular arrhythmias. Patients were randomized in a blinded fashion to receive either a monophasic or a biphasic waveform for the initial shock for conversion of induced ventricular arrhythmias (ventricular fibrillation [VF] = 53, monomorphic ventricular tachycardia [VT] = 80, polymorphic VT = 30, ventricular flutter = 8). Delivered energies for the Edmark and Gurvich waveforms were 215 +/- 11 and 171 +/- 11 J, respectively. There were no significant differences in patient characteristics, use of antiarrhythmic agents, arrhythmia cycle length, or duration of arrhythmia prior to shock for monophasic and biphasic waveform groups. The first shock for all arrhythmias was successful in 75 of 88 patients (85.2%) for the monophasic waveform compared with 81 of 83 patients (97.6%) for the biphasic waveform, p = 0.0054. The first shock for VF was successful in 22 of 28 patients (78.6%) for the monophasic waveform compared with 25 of 25 (100%) for the biphasic waveform, p = 0.0241. The Gurvich biphasic waveforms delivering a mean of 171 J were superior to Edmark monophasic waveforms delivering a mean of 215 J for transthoracic cardioversion of arrhythmias of short duration. This finding may have important implications for the development of future transthoracic defibrillators.

Adult↗
PubMed1995

Effects of optical enantiomers CK-4000(S) and CK-4001(R) on defibrillation and enhancement of shock-induced extension of action potential duration.

INTRODUCTION: Class III antiarrhythmics have been reported to lower defibrillation threshold (DFT); however, the mechanism(s) of this effect is unknown. Recent evidence suggests that DFT strength DC shocks may terminate reentrant arrhythmias through prolongation of action potential duration and refractory periods. Since Class III antiarrhythmic drugs prolong repolarization, we examined the hypothesis that these drugs enhance shock-induced action potential duration extension (APDE), which might contribute to lowering of DFT. METHODS AND RESULTS: In order to investigate the specificity of drug effects on action potential repolarization following a shock, an optical enantiomer with mixed beta-blocking and Class III effects (CK-4000) and its enantiomer with "pure" Class III antiarrhythmic effects (CK-4001) were compared against placebo in a canine defibrillation model (n = 8 per group). At the 3 mg/kg dose, the enantiomers nonstereoselectively lowered DFT voltage by 19 +/- 15% (CK-4000, P < 0.05 compared to placebo) and 25 +/- 12% (CK-4001, P < 0.05 compared to placebo), indicating that Class III antiarrhythmic actions alone were sufficient for this effect. Similarly, CK-4000 and CK-4001 at 3 mg/kg enhanced APDE (P < 0.01 compared to placebo) by 20 +/- 11% and 24 +/- 17%, respectively. APDE prolongation significantly correlated with reduction in DFT voltage for both CK-4000 (r = -0.55, P < 0.03) and CK4001 (r = -0.63, P < 0.01). At 3 mg/kg, the enantiomers stereoselectively prolonged action potential duration (APD75) by an average of 37 +/- 14% (CK-4000, P < 0.001) and 23 +/- 14% (CK-4001, P < 0.001), and ventricular effective refractory period (VERP) by 38 +/- 15% (CK-4000, P < 0.01) and 27 +/- 13% (CK-4001, P < 0.05). Prolongations of APD75 and VERP did not correlate with reductions of DFT in individual dogs. CONCLUSIONS: These results show that Class III antiarrhythmics and DFT strength shocks additively delay repolarization, which suggests that drug enhancement of APDE may contribute to their effects on DFT.

Action Potentials↗
PubMed1993

Utilization of a human intestinal epithelial cell culture system (Caco-2) for evaluating cytoprotective agents.

Human intestinal epithelial cells (Caco-2) were cultured as confluent monolayers on polycarbonate membranes in Transwells for investigating their applicability in evaluating the cytoprotective activity of sucralfate. The control experiments established a reproducible chemical method (using 0.5 mM indomethacin in Hanks' balanced salt solution) for inducing damage to the Caco-2 cell monolayers. Damage was determined by measuring changes in transepithelial electrical resistance (TEER). Twenty-day-old Caco-2 cell monolayers were significantly and reproducibly damaged (compared to buffer alone) (P < 0.001) by application of 0.5 mM indomethacin to the apical side for 1 hr. While sucralfate, at a 0.5, 2, or 5 mg/mL concentration in the buffer, was shown not to reverse (treat) the damage caused by indomethacin in this cellular model, it was able to protect (prevent) the cells from indomethacin-induced damage (P < 0.001). We observed that indomethacin-induced damage to the Caco-2 cell monolayers greatly affected the paracellular pathway since the percentage transport of [3H]methoxyinulin was significantly elevated. In contrast, protection of the Caco-2 cells with 5 mg/mL sucralfate in the presence of the damaging agent resulted in transport of the paracellular marker similar to that in the control (HBSS-treated) cell monolayers. This direct cytoprotective effect was thus independent of vascular factors at neutral pH and was observed to be dose dependent (0.5 to 5 mg/mL) when sucralfate was applied to the cells in the presence of the damaging agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Cells, Cultured↗
PubMed1993

Randomized cross-over evaluation of two adaptive pacing algorithms for the termination of ventricular tachycardia.

OBJECTIVE: In a randomized, cross-over study we evaluated the efficacy of rate adaptive constant cycle length (BURST) and autodecremental (RAMP) pacing for termination of sustained monomorphic ventricular tachycardia. METHODS: An external device capable of delivering the same types of antitachycardia pacing as the newer generation implantable cardioverter defibrillators was used. Thirty-one patients with ischemic and nonischemic cardiomyopathy and documented clinical ventricular tachycardia or ventricular fibrillation were examined during routine invasive electrophysiological studies. RAMP and BURST pacing were each attempted in 54 matched pairs of induced ventricular tachycardia. After a therapy was applied, the tachycardia was reinitiated and the other therapy applied during the second episode so that a total of 108 ventricular tachycardia episodes were studied. RESULTS: Overall efficacy of ventricular tachycardia pace termination was 69% and the time required to stop ventricular tachycardia was 14.1 +/- 11.3 seconds. The ability to terminate ventricular tachycardia by RAMP (72%) or BURST (65%) pacing was not significantly different. However, time to terminate ventricular tachycardia by RAMP (11.8 +/- 8.5 sec) was significantly shorter than by BURST (16.4 +/- 13.5), P < .001. Acceleration of ventricular tachycardia was uncommon with both pacing modes, 7/108 (7%). The ability to pace terminate ventricular tachycardia was cycle length dependent. The highest success was with ventricular tachycardia cycle length between 300 and 350 msec. The success rate decreased with faster and also slower ventricular tachycardia. CONCLUSIONS: 1. Rate adaptive pacing methods for ventricular tachycardia termination are effective and safe. 2. Autodecremental RAMP pacing afford quicker ventricular tachycardia termination than constant cycle length BURST pacing. 3. The ability to terminate ventricular tachycardia is cycle length dependent with cycle length range of 300-350 msec being most responsive to pace termination.

Adult↗
PubMed1992

New observations on atrial fibrillation before and after surgical treatment in patients with the Wolff-Parkinson-White syndrome.

The records of 342 patients who received surgical treatment for the Wolff-Parkinson-White syndrome between 1968 and 1986 were reviewed to evaluate the characteristics of atrial fibrillation. The patients were classified into two groups according to the presence (n = 166) or absence (n = 176) of documented episodes of atrial fibrillation preoperatively. The mean follow-up duration was 6 years (range 2 to 20). As compared with reports based on smaller patient groups and shorter follow-up, the study revealed several new findings. 1) During follow-up, nine patients in the atrial fibrillation group developed recurrent atrial fibrillation after a successful operation; five of these nine patients did not have associated heart disease. 2) All three patients with a history of atrial fibrillation and an accessory pathway conducting in the anterograde direction only had a successful surgical procedure and no postoperative atrial fibrillation. 3) The cycle length of atrioventricular (AV) reciprocating tachycardia was significantly shorter in the atrial fibrillation group (304 +/- 42 ms, mean +/- SD) than in the no-atrial fibrillation group (321 +/- 54 ms, p less than 0.005), and the cycle length of AV reciprocating tachycardia that degenerated into atrial fibrillation (289 +/- 26 ms) was shorter than that for the AV reciprocating tachycardia without subsequent atrial fibrillation (316 +/- 51 ms, p less than 0.005). 4) Sustained atrial fibrillation was induced in 30% of patients without a history of atrial fibrillation. 5) Atrial fibrillation occurred in four patients with an accessory pathway that conducted only in the retrograde direction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Calculating endocardial potentials from epicardial potentials measured during external stimulation.

This paper presents a boundary integral method for calculating the potential field generated by external stimulation at locations within the heart using realistic heart geometry and samples of the potential taken from the epicardial surface. This method assumes the heart is homogeneous and isotropic. To test the method we made epicardial and endocardial measurements in dogs during transthoracic pacing stimuli. From the epicardial potential measurements we predicted the endocardial potential values and compared them with the measured data. Despite the seemingly gross assumptions, the mean correlation coefficient between the measured and predicted potentials for three dogs and eleven stimulation electrode configurations was 0.985, and the mean rms error was 17%.

Action Potentials↗
PubMed1992

Three-dimensional potential gradient fields generated by intracardiac catheter and cutaneous patch electrodes.

BACKGROUND: Defibrillation may be improved if electrode configurations can be found that create a larger and more even voltage gradient field across the heart. This study determined the magnitude of the shock gradient fields generated by four nonthoracotomy electrode configurations for defibrillation. METHODS AND RESULTS: In six dogs, a catheter was inserted containing a right ventricular apical electrode (V) and a right atrial electrode (A). A cutaneous patch electrode (P) was placed on the left lateral thorax. Shock potentials were recorded simultaneously from 128 electrodes in the left ventricular and right ventricular subepicardium and subendocardium, ventricular septum, and atria. With the chest closed, 50-mA shocks were given during diastole via the following lead configurations: V----A (V, cathode; A, anode); V----P; V----A+P; and V+A----P. Potential gradients were calculated at the subepicardium and subendocardium in millivolts per centimeter per volt of shock. In most dogs, the V----A+P configuration produced higher gradients throughout the ventricles than did V----A, V----P, or V+A----P. The maximum potential gradient was smaller for the V+A----P configuration than for V----A, V----P, or V----A+P. The gradient fields for the configurations with the catheter alone or combined with P were uneven. CONCLUSIONS: It is possible to estimate shock gradient fields in three dimensions. Of the four configurations tested, V----A+P produced the highest gradients and V+A----P produced the lowest high gradient. The gradient fields were uneven throughout the ventricles.

Animals↗
PubMed1992

Effect of Ebstein's anomaly on short- and long-term outcome of surgically treated patients with Wolff-Parkinson-White syndrome.

BACKGROUND: Ebstein's anomaly is the most commonly occurring congenital abnormality associated with the Wolff-Parkinson-White (WPW) syndrome. However, the effects of Ebstein's anomaly on the risks and benefits of surgical ablation of accessory pathways in patients with WPW syndrome are unknown. METHODS AND RESULTS: This study compared the long-term outcome of 38 WPW patients with Ebstein's anomaly undergoing accessory pathway ablation to a reference population of 384 similarly treated patients without the anomaly. Ebstein's anomaly was mild in 21 patients (55%) and moderate-to-severe in 17 patients (45%). Sixteen patients (42%) required tricuspid valve surgery, and 23 (61%) had an atrial septal defect or patent foramen ovale repaired. Baseline clinical characteristics and preoperative clinical arrhythmias were similar in both groups. Ten-year survival was 92.4% and 91.2% for patients with and without Ebstein's anomaly, respectively (p = NS). During a mean follow-up of 6.2 +/- 3.8 and 5.3 +/- 3.6 years, 82% of patients with and 90% without Ebstein's anomaly had either clinically insignificant or no arrhythmias, and 18% versus 10% reported symptoms suggesting arrhythmias lasting longer than 1 minute, respectively. Atrial fibrillation was reduced postoperatively to 9% (p less than 0.001) in patients with and to 4% (p less than 0.001) in those without the anomaly. Fewer hospitalizations were reported postoperatively by 90% versus 96% of patients with and without Ebstein's anomaly; 9.4% versus 6.0% of patients were disabled at follow-up, respectively (p = NS). CONCLUSIONS: Patients with Ebstein's anomaly are improved significantly after accessory pathway ablation. The presence of this anomaly should not preclude accessory pathway ablation in these patients.

Adolescent↗