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Biomedical subjects

M S Chang

Publications and source records attributed to M S Chang.

At least 271 records · Page 15Linked to original sources
PubMed1994

Radiofrequency catheter ablation of sustained intraatrial reentrant tachycardia in a patient with mirror-image dextrocardia.

INTRODUCTION: There has been limited experience with radiofrequency catheter ablation in patients with dextrocardia. This report describes a 37-year-old man who had secundum type atrial septal defect, mirror-image dextrocardia, and drug-refractory atrial tachycardia, in whom catheter-mediated radiofrequency energy successfully eliminated the tachycardia without complication. METHODS AND RESULTS: On electrophysiologic study, the atrial tachycardia could be induced and terminated by atrial extrastimulation or rapid atrial pacing. Mixed resetting response pattern and manifest entrainment were also demonstrated. These findings suggested that the mechanism of atrial tachycardia might be related to reentry with an excitable gap. Because of the mirror-image dextrocardia, biplane fluoroscopy was adjusted to the right anterior oblique (RAO) 60 degrees and left anterior oblique (LAO) 30 degrees positions. Inducibility of the tachycardia was completely abolished after the sixth application of radiofrequency current (30 W). It was noted that the successful electrogram preceded the onset of P wave during atrial tachycardia by about 40 msec. CONCLUSION: This report presents another case in which radiofrequency catheter ablation was used in a patient with dextrocardia. Atrial tachycardia in patients with congenital heart disease may be difficult to control pharmacologically; however, the use of radiofrequency catheter ablation could be recommended as an alternative to medication and surgery.

Adult↗
PubMed1994

Sustained atrial tachycardia in adult patients. Electrophysiological characteristics, pharmacological response, possible mechanisms, and effects of radiofrequency ablation.

BACKGROUND: Mechanisms and electropharmacological characteristics in adult patients with atrial tachycardia (AT) are not well described. We proposed that a combination of electropharmacological characteristics, recording of monophasic action potential, and effects of radiofrequency ablation could further determine the mechanisms and achieve a new classification in adults with various types of AT because they were important in regard to the correlation between mechanisms and pathophysiology, clinical syndrome, and responses to specific pharmacological or nonpharmacological therapies. METHODS AND RESULTS: Thirty-six patients (11 female, 25 male; mean age, 57 +/- 13 years) with AT were referred for electropharmacological studies and radiofrequency ablation. Resetting response pattern, entrainment phenomenon, recording of monophasic action potential, serial drug test, response to Valsalva maneuver, endocardial mapping technique, and radiofrequency ablation were performed. Seven patients had automatic AT provocable with isoproterenol; neither initiation nor termination was related to programmed electrical stimulation. The other 29 patients had AT initiated or terminated by electrical stimulation and mechanisms related to triggered activity or reentry; nine of them needed isoproterenol to facilitate initiation of AT, associated with delayed afterdepolarization in monophasic action potential. All responded to adenosine (15 to 60 micrograms/kg) and Valsalva maneuver. Dipyridamole terminated AT and decreased the slope of afterdepolarization. Afterdepolarization was not found in the patients with automatic or reentrant AT. In 40 of 41 (98%), AT was ablated successfully, with late recurrence in 2 of 40 (5%) (follow-up, 18 +/- 4 months). CONCLUSIONS: This study demonstrates the diverse mechanisms and electropharmacological characteristics of AT in adults. Furthermore, radiofrequency ablation of various types of AT could achieve high success and low recurrence rates.

Adult↗
PubMed1994

Incidence, significance, and pharmacological responses of catheter-induced mechanical trauma in patients receiving radiofrequency ablation for supraventricular tachycardia.

BACKGROUND: Catheter-induced mechanical trauma is unfavorable during electrophysiological study. However, its incidence, significance, and pharmacological responses in patients receiving radiofrequency ablation for supraventricular tachycardia have not been investigated. METHODS AND RESULTS: A prospective study was performed in 666 consecutive patients with documented, symptomatic supraventricular tachycardia. All had been referred for electrophysiological study and radiofrequency ablation. Catheter-induced mechanical trauma was defined by either disappearance of or change in preexcitation pattern induced by the electrode catheters or noninducibility of tachycardia after the electrode catheter-induced termination of tachycardia, confirmed by electrophysiological study. Adenosine, isoproterenol, and atropine were serially administered 1 hour after the mechanical trauma to study pharmacological response. "Rescue" radiofrequency ablation was defined as delivery of radiofrequency energy just at the presumed ablation site immediately after the mechanical trauma. Of the 666 patients, 254 had atrioventricular (AV) nodal reentrant tachycardia, 367 patients had accessory pathways, 30 patients had atrial tachycardia, and 15 had atrial flutter. Catheter-induced mechanical trauma occurred in 17 patients (2.6%): 4 patients had AV nodal reentrant tachycardia, 9 had accessory pathways, and 4 had atrial tachycardia. Five patients had such episodes during the placement of electrode catheters and 12, during mapping and ablation procedures. Of the 4 patients with AV nodal reentrant tachycardia, 3 had mechanical trauma on the retrograde fast pathway and 1, on the antegrade slow pathway. In the 9 patients with accessory pathways, those pathways were located in the left free wall in 4 patients, right free wall in 1, right posteroseptum in 1, and right anteroseptum in 3. Atrial tachycardia was more easily traumatized than AV nodal reentrant tachycardia (P < .01) and than accessory pathways (P < .01). The clinical courses of mechanical trauma were variable: 1 patient had spontaneous recovery within 1 week, 5 patients had recurrence of tachycardia within 3 months, and the rest have been free of tachycardia from 3 to 35 months. The recurrence rate was higher in patients with mechanical trauma than in those without (33.3% versus 3.5%, P < .0001) despite rescue radiofrequency ablation given in 7 patients. Pharmacological agents were generally unable to revive the traumatized tissues, and recurrence was unpredictable. CONCLUSIONS: Catheter-induced mechanical trauma was not common in patients receiving radiofrequency ablation for supraventricular tachycardia. Their clinical courses were variable, and pharmacological manipulation offered little assistance. More than half of the patients had long-term cures. However, the recurrence rate was, on the whole, significantly high despite rescue radiofrequency ablation. There is a need for great caution in the placement of electrode catheters in every patient during electrophysiological study and radiofrequency ablation.

Adenosine↗
PubMed1994

Atrial pacing-induced reverse alternating Wenckebach periods. A common electrophysiologic phenomenon in patients with dual atrioventricular nodal pathways.

Reverse alternating Wenckebach periods (RAWP) have rarely been described, and the significance of dual AV nodal pathways in atrial pacing-induced RAWP is unknown. Forty-five of 50 consecutive patients (M/F = 23/27, mean age 40 +/- 5 years) with common type AV nodal reentrant tachycardia had discontinuous antegrade conduction curves. Atrial pacing revealed that pattern A RAWP (23 patients) had the fourth paced beat conducted over the fast pathway, and pattern B (18 patients) over the slow pathway. Four patients had both pattern A and B RAWP during different pacing cycle lengths. All episodes of atrial pacing-induced RAWP emerged from (or started as) 3:2 AH block, which thereafter were followed by runs of 2:1 AH block. Comparisons between patterns A and B showed (1) maximal atrial pacing cycle length with RAWP was longer in pattern A; (2) A2H2-A1H1 and A4H4-A1H1 were significantly greater in pattern B; (3) A2H2-A4H4 and H2A4/A2H2 were significantly greater in pattern A. It is concluded that atrial pacing-induced RAWP is a common electrophysiologic phenomenon in patients with dual AV nodal pathways. Furthermore, intermittent slow pathway conduction associated with different AnHn and HnAn+2 parameters helped the interpretation of different conduction patterns.

Adult↗
PubMed1994

Atrial demand pacing in patients with symptomatic sick sinus syndrome.

Atrial demand pacing provides a physiological, simply implemented, and less costly alternative of cardiac stimulation in symptomatic sick sinus syndrome (SSS) patients. Hindrance from widespread use stems mainly from the potential development of high degree AV block and persistent atrial fibrillation. A reappraisal of atrial pacing is now justified as we gain more clinical information. In this study we examined retrospectively the clinical course of 22 well-selected SSS patients paced in AAI mode for 30 +/- 29 months. Two patients had infrequent short-run atrial tachyrhythmia before implantation. There was an early lead dislodgement which required repositioning later. Three acute threshold increments were noted which necessitated a change in atrial pacing site in one and short-term steroid use in the other two. No other sensing, pacing or operative complication occurred and all pacing systems performed well. AII patients survived during follow-up and no patient developed congestive heart failure, though depressed left ventricular function was found in three preoperatively. No high degree AV block was encountered. Four patients presented paroxysmal atrial fibrillation (PAF) 25 +/- 16 months after the procedure, of whom one developed chronic atrial fibrillation. No single factor predicted the development of PAF. Resumption of normal pacemaker function always occurred immediately in the pause following cessation of PAF and no revision of pacing mode was required in the patient with chronic AF. Symptomatic relief was obtained in all patients. In summary, single chamber, single rate atrial pacing remains a physiologic, reliable, economic and easily implemented pacing modality affordable to a number of sick sinus patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Right atrial pacing for risk stratification in patients with angina pectoris.

Right atrial pacing (RAP) has been used to assess the physiologic impact of coronary artery disease (CAD). Several variables have served as markers of pacing-induced myocardial ischemia or for predicting disease severity, but their clinical implications remain uncertain. Therefore, three-stage RAP was performed to evaluate whether this strategy could predict the disease severity of CAD and foretell subsequent major cardiac events in 49 patients with typical chest pain. RAP was considered positive if 1 mm or more of horizontal or downward ST depression developed. Of the 49 cases, 28 had positive RAP (group A), and the remaining 21 had negative RAP (group B). For hemodynamic data, early positive RAP had the highest post-pacing left ventricular end-diastolic pressure (LVEDP). The LVEDP increased significantly in Group A (p < 0.05), whereas there was no apparent change in group B. Furthermore, group A (36%) tended to develop typical chest pain more easily than group B (14%), but this was statistically insignificant. Group A had a higher incidence of multivessel disease than that of group B (p < 0.001), whereas group A had a lower incidence of non-significant CAD than that of group B (p < 0.001). During the mean two-year follow-up period, there were 23 major cardiac events (MCE) in group A in contrast to two episodes in group B (p < 0.005). The early positive subset had 18 episodes, whereas the late positive subset had only five episodes (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Secondary hypertension due to renin secreting tumor: a case report.

We report a 20-year-old female with severe hypertension, hypokalemia, hyperaldosteronism and elevated level of plasma renin activity (PRA). The clinical diagnosis of renin secreting tumor of left kidney was made before surgery by the lateralization of plasma renin activity via selective renal venous blood sampling and CT scan of kidney. Prompt normalization of blood pressure and decrease of PRA and aldosterone levels were found after surgical removal of the tumor. The pathological findings showed a juxtaglomerular cell tumor.

Adenocarcinoma↗
PubMed1993

Diastolic compliance of hypertrophied ventricle is not acutely altered by pharmacologic agents influencing active processes.

OBJECTIVE: To test, by studying the acute effects of drugs that influence active processes, the hypothesis that in humans with marked ventricular hypertrophy, reduced chamber compliance is primarily caused by passive structural changes. DESIGN: An uncontrolled (before-after) study. SETTING: University Medical Center. PATIENTS: Fourteen patients with ventricular hypertrophy (19 +/- 4.5-mm diastolic-wall thickness) and normal resting systolic function were studied while they had invasive cardiac catheterization. INTERVENTION: Intravenous beta-blocker (esmolol) or calcium channel blocker (verapamil) or both. MEASUREMENTS: Left ventricular function was determined by pressure-volume relations. Volume was measured using conductance catheter, providing a continuous voltage signal proportional to chamber volume. Pressure was measured by micromanometer. Cardiac-specific assessment of change in chamber contractility and diastolic compliance due to each drug was determined. RESULTS: Both drugs lowered contractility by approximately 30% (P < 0.01). Esmolol slowed relaxation and reduced early peak filling rate, whereas verapamil delayed the time to peak filling (all P < 0.05). In contrast to the effects of both drugs on active contraction and early diastole, late-diastolic compliance was unaltered, and end-diastolic pressure-volume relations were almost identical. CONCLUSION: Neither beta-receptor nor calcium channel blockade acutely alters left ventricular compliance despite substantial active effects manifest in systole and early diastole. This supports the notion that chamber compliance is principally determined by passive structural elements in the heart rather than by active processes.

Adrenergic beta-Antagonists↗
PubMed1993

Different pressure gradients can be produced in a fixed stenosis--an in vitro study.

An in vitro study was conducted, using a stenotic model to demonstrate that different pressure gradients can be produced by the same degree of valvular stenosis. This model is comprised of two cylindric chambers with a diaphragm in the center which had a small central hole. An injector was connected to one end of the prestenotic chamber to produce a steady pulsed flow. A rubber tube was connected to the other end of the poststenotic chamber and led upward to a large reservoir which provided a constant afterload pressure. Two pressure transducers were attached to the two connecting tubes, both linked with two pigtail catheters which were accommodated in the chambers just before and after the stenotic diaphragm. Two sets of injection volumes (20 and 30 ml) and multiple injections with different flow rates (5, 10, 15,...49 ml/s) were administered and resulting pressures measured by the two transducers were recorded. Results showed that different pressure gradients could be produced using the same injection volume, the same afterload, and the same degree of stenosis. The greater the flow rate, the higher the pressure gradient. Good correlation existed between the pressure gradient and the injection flow rate (r = 0.95 and 0.97 for the study groups receiving 20 and 30 ml injection volumes, respectively; p < 0.001 in all comparisons). Thus, a higher pressure gradient may not necessarily indicate a severe degree of valvular stenosis. Evaluation of a stenotic lesion should not be made from the degree of pressure gradient alone--other hemodynamic conditions should also be taken into account.

Blood Flow Velocity↗
PubMed1993

Increased aortic endothelial death and enhanced transendothelial macromolecular transport in streptozotocin-diabetic rats.

Hypertension, cigarette smoking and diabetes mellitus are well-known risk factors for atherosclerosis and coronary heart disease. Repeated endothelial cell injury and increased lipid entry have been suggested as initiating events in atherogenesis. Our previous studies have demonstrated that the frequency of endothelial cell death and associated endothelial permeability were significantly increased in the aorta of spontaneously hypertensive rats and chronic oral nicotine-treated rats. In the present investigation, we examined the hypothesis that diabetes also increases the frequency of arterial endothelial cell death and hence transendothelial macromolecular transport, which may have some implications in increasing lipid entry and thus accelerating atherogenesis. Diabetes was induced in 15 male Sprague-Dawley rats by intraperitoneal injection of 60 mg streptozotocin per kg body weight. The duration of diabetes was 6 weeks. A group of 15 age-matched rats, injected only with the buffer and maintained over the same time period, served as the controls. In en face preparations of the thoracic aorta, IgG-containing dead endothelial cells were identified by an indirect immunoperoxidase method, and endothelial leakage to Evans blue-albumin complexes was quantified by fluorescence microscopy. Diabetic rats, compared to control rats, had significantly higher values for the frequency of endothelial cell death (0.77 +/- 0.10% vs 0.38 +/- 0.04%; p < 0.005 by two-tailed, unpaired Student's t-test) and the number density of Evans blue-albumin leaky foci (4.33 +/- 0.48/mm2 vs 2.99 +/- 0.38/mm2; p < 0.05 by two-tailed, unpaired t-test) in the aorta.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Arrhythmogenicity of catheter ablation in supraventricular tachycardia.

To evaluate arrhythmogenicity in patients who receive a modified direct-current (DC) shock ablation (distal pair of electrodes connected in common as the cathode) or radiofrequency (RF) ablation of supraventricular tachycardia, a prospective study was performed with signal-averaged ECG, 24-hour Holter monitoring, electrophysiologic study (EPS) for ventricular tachycardia (VT), and treadmill exercise test. Sixty-nine consecutive patients with documented paroxysmal supraventricular tachycardia were included. Twenty-eight patients proved to have atrioventricular nodal reentrant tachycardia, and 41 patients had atrioventricular reciprocating tachycardia that involved accessory atrioventricular pathways. The first 34 patients received DC shock ablation and the other 35 patients received RF ablation. Signal-averaged ECG, Holter monitoring, and EPS for VT were performed before ablation, immediately after ablation, then 1 week, 2 weeks (Holter monitoring), 1 month (except EPS), and 3 months after ablation. Treadmill exercise testing was performed before ablation, and at 1 week and 3 months after ablation. The root mean square, low-amplitude signal and QRS duration of signal-averaged ECG disclosed no significant change after either DC or RF ablation up to 3 months. Late potential developed in only one patient in the DC shock group and it was considered to be innocuous because neither VT nor ventricular fibrillation was noted or induced. Increases in the number of ventricular premature contractions and in short-run VT were detected by Holter monitoring in the first week after either mode of ablation (p < 0.001 for the DC shock group; p < 0.05 for the RF group), which were greater (p < 0.05) and lasted longer in the DC shock group than in the RF group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Usefulness of serial follow-up electrophysiologic studies in predicting late outcome of radiofrequency ablation for accessory pathways and atrioventricular nodal reentrant tachycardia.

A total of 408 patients received radiofrequency catheter ablation for paroxysmal supraventricular tachycardia, and 326 patients underwent serial follow-up electrophysiologic studies (early and late) after initially successful radiofrequency catheter ablation of accessory pathways (group 1, 186 patients with Wolff-Parkinson-White syndrome) and slow atrioventricular (AV) nodal pathways (group 2, 140 patients with AV nodal reentrant tachycardia). Among the patients in group 1, early (4 +/- 1 days) and late (129 +/- 14 days) studies found recurrent conduction through the accessory pathways in 12 and 16 patients, respectively. During a follow-up period of 21 +/- 7 months, recurrence of accessory pathway-mediated tachyarrhythmias was noted in six patients. Of these six patients, all had tachycardia inducible in the late study but not in the early study. Among the patients in group 2, four had recurrence of AV nodal reentrant tachycardia during a follow-up of 16 +/- 6 months. Of the four patients, one had tachycardia inducible in the early (4 +/- 1 days) study and three in the late (130 +/- 12 days) study. The results demonstrated that the early study was not as sensitive as the late follow-up electrophysiologic study in predicting late outcome of radiofrequency ablation, but both the early and late studies had a high total predictive accuracy (> 90%) in groups 1 and 2. Furthermore, only 4 of the 326 patients had initial evidence of recurrent tachycardia activated by programmed electrical stimuli during follow-up studies, suggesting that follow-up electrophysiologic studies in asymptomatic patients are not warranted.

Adult↗
PubMed1993

Clinical features and electrophysiologic characteristics of accessory atrioventricular pathways and atrioventricular nodal reentrant tachycardia: comparative study between young and elderly patients.

Information focused on elderly patients with paroxysmal supraventricular tachycardia, and a comparative study between the elderly and younger patients was limited. The aim of this study was to investigate the clinical features and electrophysiologic characteristics in elderly patients (> or = 65 years of age) with accessory atrioventricular pathway-mediated tachyarrhythmia or atrioventricular nodal reentrant tachycardia. Electrophysiologic studies of 45 elderly patients with accessory pathway-mediated tachyarrhythmia and 47 elderly patients with atrioventricular nodal reentrant tachycardia were performed. When compared with younger patients, the elderly patients had a similar incidence of critical clinical manifestation, higher incidence of other cardiac disease or systemic disease, similar inducibility of tachycardia, greater baseline electrophysiologic parameters (sinus node, atrioventricular node, atrium and ventricle), and poorer properties of accessory pathways and dual atrioventricular nodal pathways. These results suggest that conduction properties of accessory pathways and dual atrioventricular nodal pathways were poorer in elderly patients, but similar critical manifestations and tachycardia events were found in elderly and younger patients.

Adolescent↗
PubMed1993

Effect of pravastatin on fatty acid profile of low density lipoprotein in patients with hypercholesterolemia.

We gave pravastatin, an HMG-CoA reductase inhibitor, to 21 hypercholesterolemic patients for 12 weeks after they had been on dietary therapy for 12 weeks. In addition to inducing a significant reduction of total cholesterol and LDL-cholesterol, pravastatin significantly decreased the proportion of linoleic acid (18:2) and increased that of saturated (FA) (16:0 and 18:0) in the cholesterol ester of LDL. Linoleic acid was also reduced in the triglyceride of LDL. Besides, monounsaturated FA (16:1 and 18:1) were increased in the cholesterol ester, triglyceride and phospholipid of LDL, but the changes in monounsaturated FA were not statistically significant. The effect of pravastatin on the FA profile of LDL was similar to that of fibric acid derivatives. The mechanism as well as the clinical implication of these changes await further investigation.

Adult↗
PubMed1993

Serial electrophysiological studies in the late outcome of radiofrequency ablation for accessory atrioventricular pathway-mediated tachyarrhythmias.

Assessment of radiofrequency ablation for accessory pathway-mediated tachyarrhythmias is evaluated by a variety of methods in different institutes. However, the predictive values of these methods are not known. Therefore, serial electrocardiograms (12-lead, 24-h Holter monitoring), reviews of symptoms, and electrophysiological studies (immediate, early, late) were used in this institute to evaluate and predict late outcome in 150 patients with 174 accessory pathways. Late electrophysiological study (130 +/- 11 days after ablation) detected a larger proportion of patients (11.1%) with late ablation failure than immediate (1.3%), or early (7.0%) electrophysiological study, or serial electrocardiograms (1.4%), or reviews of symptoms (1.4%); it showed that patients with concealed accessory pathways (11.4%), energy delivered to the ventricular sites of left concealed accessory pathways (23.3%), and those without a recordable accessory pathway activation potential (14.8%) had a higher incidence of recurrent conduction, and also provided the most accurate information for predicting late outcome with higher sensitivity (100%) and predictive accuracy (100%) than other tests. It is concluded that the value of serial electrocardiograms, symptom review, immediate and early electrophysiological studies should be downgraded, and that the late electrophysiological study has a high predictive value for late outcome and helps understanding of the residual changes in accessory pathways after initially successful ablation.

Adolescent↗
PubMed1993

Radiofrequency ablation of left-sided accessory atrioventricular pathways in patients with unusual coronary sinus.

Four patients with left-sided accessory pathways (APs) and unusual coronary sinus (CS) received radiofrequency ablation. Unusual CS included occlusion of CS (patient 1), acute angulation of proximal CS (patients 2 and 3), and narrowing of CS orifice and proximal segment (patient 4). CS catheterization and AP mapping along the CS could not be performed in the four patients. Radiofrequency ablation by left ventricular retrograde technique for the manifest left posteroseptal AP (patient 1), concealed left posterior AP (patient 2), and transseptal left atrial technique for the manifest left posteroseptal AP (patient 3) and manifest left posterior AP (patient 4) were performed successfully without CS catheter guidance. This study suggests that radiofrequency ablation of left-sided AP with unusual CS is feasible by some special techniques.

Adult↗