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Biomedical subjects

Shih-Ann Chen

Publications and source records attributed to Shih-Ann Chen.

At least 91 records · Page 5Linked to original sources
PubMed2003

Effects of continuous enhanced vagal tone on dual atrioventricular node and accessory pathways.

BACKGROUND: The aim of this study was to test the electrophysiological effects of continuous enhanced vagal tone on dual atrioventricular (AV) nodal and accessory pathways. METHODS AND RESULTS: This study included 10 patients with typical, slow-fast AV nodal reentrant tachycardia (AVNRT) and 10 patients with AV reciprocating tachycardia. Electrophysiological data were measured before and during continuous vagal enhancement by using phenylephrine infusion (0.6 to 1.5 microg/kg per min). For patients with AVNRT, during phenylephrine infusion, 1:1 conduction times over the anterograde fast and slow and retrograde fast pathways were prolonged (453+/-64 to 662+/-120 ms, P<0.001; 379+/-53 to 443+/-95 ms, P<0.05; 405+/-112 to 442+/-118 ms, P<0.05). The effective refractory period and functional refractory period of the anterograde fast pathway were prolonged with phenylephrine (394+/-73 to 544+/-128 ms, P<0.001; 454+/-60 to 596+/-118 ms, P<0.001). In contrast, the effective refractory period and functional refractory period of the anterograde slow and retrograde fast were not significantly changed. No significant change was observed in the conduction or refractoriness of the accessory pathways in patients with AV reciprocating tachycardia nor in atrial or ventricular refractoriness. CONCLUSIONS: Enhanced vagal tone produces disparate effects on the refractoriness of the slow and fast AV nodal conduction pathways, with the anterograde fast pathway being the most sensitive. These changes are conducive to induction of AVNRT with a premature atrial complex and may explain in part the relatively common occurrence of AVNRT during sleep or other periods of presumed increased parasympathetic tone.

Adult↗
PubMed2003

Effect of atrial dilatation on electrophysiologic properties and inducibility of atrial fibrillation.

INTRODUCTION: Atrial dilatation may play an important role in the occurrence of atrial fibrillation (AF) in clinical situations. However, the electrophysiologic characteristics of dilated atria are still unclear. METHODS AND RESULTS: In 18 isolated Langendorff-perfused canine hearts (14.6 +/- 2.2 kg), we measured atrial effective refractory periods (ERPs) at four different sites, conduction velocity and percentage of slow conduction on the right atrium (using a high-density electrode plaque), and assessed the inducibility of AF at the baseline (0 cm H(2)O) and high (15 cm H(2)O) atrial pressure. The atrial ERPs did not change significantly, but the dispersion of ERP increased significantly (40 +/- 18 vs 25 +/- 9 vs ms, p = 0.01) during high atrial pressure. The percentage of slow conduction (< 25 cm/s) over the mapping area, and the inducibility of AF increased during high atrial pressure (23.7 +/- 10.2 % vs 32.1 +/- 12.5 %, p = 0.02). The AF inducibility significantly correlated with the ERP dispersion (R = 0.75, p < 0.001) and maximal percentage of slow conduction (R = 0.88, p < 0.001). Furthermore, ERPs were significantly shorter in the induced AF group than those without induced AF (68 +/- 17 vs 84 +/- 16 ms, P < 0.05). CONCLUSIONS: The increased inhomogenity in atrial electrophysiological properties during atrial dilatation contributed to the inducibility of AF.

Animals↗
PubMed2003

Use of enalapril to facilitate sinus rhythm maintenance after external cardioversion of long-standing persistent atrial fibrillation. Results of a prospective and controlled study.

AIMS: This study aimed to assess whether enalapril could improve cardioversion outcome and facilitate sinus rhythm maintenance after conversion of chronic atrial fibrillation (AF). METHODS AND RESULTS: Patients with chronic AF for more than 3 months were assigned to receive either amiodarone (200mg orally 3 times a day; group I: n=75) or the same dosage of amiodarone plus enalapril (10mg twice a day; group II: n=70) 4 weeks before scheduled external cardioversion. The end-point was the time to first recurrence of AF. In 125 patients (86.2%), AF was converted to sinus rhythm. Group II had a trend to a trend to a lower rate of immediate recurrence of AF than group I did (4.3% vs 14.7%, P=0.067). Kaplan-Meier analysis demonstrated a higher probability of group II remaining in sinus rhythm at 4 weeks (84.3% vs 61.3%, P=0.002) and at the median follow-up period of 270 days (74.3% vs 57.3%, P=0.021) than in group II. CONCLUSIONS: The addition of enalapril to amiodarone decreased the rate of immediate and subacute arrhythmia recurrences and facilitated subsequent long-term maintenance of sinus rhythm after cardioversion of persistent AF.

Adolescent↗
PubMed2003

Monophasic action potential-like electrocardiogram simulating acute myocardial infarction.

Monophasic action potential-like electrocardiogram simulating acute myocardial infarction has been reported in patients with hyperkalemia. We report two cases presenting marked diffuse RS-T elevation resembling monophasic action potential. They had abnormal electrolyte levels, including hyperkalemia and hypocalcemia in case 1 and hypokalemia and hypocalcemia in case 2. The ECG abnormality returned to baseline after correction of potassium and calcium. We conclude that monophasic action potential-like electrocardiogram is caused by electrolyte disturbance other than acute myocardial infarction.

Action Potentials↗
PubMed2003

Utility of patient-activated cardiac event recorders in the detection of cardiac arrhythmias.

BACKGROUND: Patient-activated event recorders are useful for the diagnosis of arrhythmia in patients with palpitation and presyncope. However, the utility of event recorders in patients suspected of arrhythmia but presenting with other symptoms is not clear. Furthermore, the factors influencing their utility have not been evaluated. METHODS: Event recorder reports of six hundred and sixty consecutive patients referred due to clinical suspicion of cardiac arrhythmia were reviewed. We divided symptoms into four groups: palpitation, presyncope, chest tightness, and dyspnea. We calculated the diagnostic yield according to patients' symptoms reported on the record, and analyzed the factors affecting the utility of event recorders. RESULTS: The overall diagnostic yield was 64%, and those of palpitation, presyncope, chest tightness, and dyspnea were 66%, 57%, 51% and 60%, respectively. The most common five findings in our patients were sinus rhythm (36%), sinus tachycardia (30%), atrial premature complex (14%), ventricular premature complex (12%), and atrial fibrillation/atrial flutter (7%). The recording duration (8 +/- 4 days) was short in the present study, but the overall diagnostic yield was similar to those of previous ones. Women had lower diagnostic yields than men, especially in atrial flutter-fibrillation. The diagnostic yield was not influenced by age, ordered doctors, or history of cardiovascular disease. CONCLUSIONS; Patient-activated event recorders provided a good diagnostic yield in patients with different presentations of cardiac arrhythmia, and women had lower diagnostic yield in atrial flutter-fibrillation.

Arrhythmias, Cardiac↗
PubMed2003

Use of fluoroscopic views for detecting Marshall's vein in patients with cardiac arrhythmias.

INTRODUCTION: Recently, several studies showed that focal atrial fibrillation (AF) can be initiated by ectopic beats from the vein of Marshall (VOM). However, the incidence and best fluoroscopic views of VOM have never been reported. METHODS AND RESULTS: 106 patients (Non-AF = 52, AF = 54) underwent balloon-occluded coronary sinus angiography using seven fluoroscopic views (PA, Lateral, RAO 30 degrees, RA 30 degrees + Caudal 20 degrees, LAO 30 degrees, LAO 60 degrees, LAO 60 degrees + Cranial 20 degrees ). The total incidence of VOM was 74.5% (79/106), without significant difference in age (81.1 vs. 71.0%, >65 vs. <or=65 yrs, p = 0.257) and sex (male vs. female = 72.7 vs. 77.5%, p = 0.585). Furthermore, similar incidence of VOM was noted in patients with Non-AF (71.2%) and AF group (77.8%, p = 0.434). The RAO 30 degrees fluoroscopic view can demonstrate all the left atrial veins and VOM. However, only the LAO 30 degrees fluoroscopic view could confirm VOM and differentiate it from left atrial veins (after vs. before junction of coronary sinus and great cardiac vein, respectively). CONCLUSION: VOM was equally distributed in patients with different arrhythmias, and the appropriate fluoroscopic view was important for the differential diagnosis of VOM and left atrial veins.

Adolescent↗
PubMed2003

Is the fascicle of left bundle branch involved in the reentrant circuit of verapamil-sensitive idiopathic left ventricular tachycardia?

The exact reentrant circuit of the verapamil-sensitive idiopathic left VT with a RBBB configuration remains unclear. Furthermore, if the fascicle of left bundle branch is involved in the reentrant circuit has not been well studied. Forty-nine patients with verapamil-sensitive idiopathic left VT underwent electrophysiological study and RF catheter ablation. Group I included 11 patients (10 men, 1 woman; mean age 25 +/- 8 years) with left anterior fascicular block (4 patients), or left posterior fascicular block (7 patients) during sinus rhythm. Group II included 38 patients (29 men, 9 women; mean age 35 +/- 16 years) without fascicular block during sinus rhythm. Duration of QRS complex during sinus rhythm before RF catheter ablation in group I patients was significant longer than that of group II patients (104 +/- 12 vs 95 +/- 11 ms, respectively, P=0.02). Duration of QRS complex during VT was similar between group I and group II patients (141 +/- 13 vs 140 +/- 14 ms, respectively, P=0.78). Transitional zones of QRS complexes in the precordial leads during VT were similar between group I and group II patients. After ablation, the QRS duration did not prolong in group I or group II patients (104 +/- 11 vs 95 +/- 10 ms, P=0.02); fascicular block did not occur in group II patients. Duration and transitional zone of QRS complex during VT were similar between the two groups, and new fascicular block did not occur after ablation. These findings suggest the fascicle of left bundle branch may be not involved in the antegrade limb of reentry circuit in idiopathic left VT.

Adolescent↗
PubMed2003

Pathophysiology of the pulmonary vein as an atrial fibrillation initiator.

The basic electrophysiologic studies have proved the arrhythmogenic mechanisms of the pulmonary vein as an atrial fibrillation initiator; the mechanisms include enhanced automaticity, triggered activity, and microreentry from myocardial sleeves inside pulmonary veins. Immunohistology study has proved the conduction characteristics of pulmonary vein myocardium, and further study of ionic currents are important for understanding atrial fibrillation initiation from the pulmonary vein.

Animals↗
PubMed2003

Novel concept of atrial tachyarrhythmias originating from the superior vena cava: insight from noncontact mapping.

INTRODUCTION: Information about the activation patterns inside the superior vena cava (SVC) and entry and exit sites at the SVC-right atrial (RA) junction during SVC tachyarrhythmia is limited. METHODS AND RESULTS: A detailed characterization of electrophysiologic mechanisms and ablation strategies was performed using a noncontact three-dimensional mapping system in two cases of SVC tachycardia. The first case demonstrated SVC tachycardia originating from an ectopic focus inside the SVC, with sustained depolarization and conduction to the atrium. Entry and exit sites across the SVC-RA junction were located very close to each other. The second case demonstrated two different reentrant circuits, one inside the SVC and the other into and out of the SVC-RA junction. The entry and exit sites were located far away from each other. CONCLUSION: Noncontact mapping may help to reveal the mechanism of SVC tachyarrhythmias and to locate entry and exit sites at the SVC-RA junction as a guide for catheter ablation.

Aged↗
PubMed2003

P wave polarities of an arrhythmogenic focus in patients with paroxysmal atrial fibrillation originating from superior vena cava or right superior pulmonary vein.

INTRODUCTION: The superior vena cava (SVC) and right superior pulmonary vein (RSPV) are anatomically close structures. Using 12-lead ECG may facilitate identification of ectopic foci from SVC or RSPV. The aim of this study was to assess whether P wave polarity on surface ECG is helpful in distinguishing an arrhythmogenic focus of paroxysmal atrial fibrillation (AF) from SVC or RSPV. METHODS AND RESULTS: Thirty-four patients with paroxysmal AF from the SVC (group I: 17 patients, 10 men and 7 women; mean age 57 +/- 12 years) or RSPV (group II: 17 patients, 15 men and 2 women, mean age 62 +/- 14 years) underwent electrophysiologic study and radiofrequency (RF) catheter ablation. All of the AF foci were confirmed by successful ablation. P wave polarities on surface ECG inferior leads were positive during sinus rhythm and ectopic beats in both groups. Leads I, aVR, aVL, and V1 were further analyzed. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) in predicting an arrhythmogenic focus of AF from SVC or RSPV were provided. P wave polarity in lead aVR was negative in all 34 patients. P wave polarity in lead V1 was positive in 47.1% of SVC ectopy but positive in all RSPV ectopy. The combination of a biphasic or isoelectric P wave polarity in lead V1 or a biphasic P wave polarity in lead aVL had a sensitivity of 71%, specificity of 82%, PPV of 80%, and NPV of 74% in predicting an arrhythmogenic focus of AF from SVC. CONCLUSION: P wave polarity in leads V1 and aVL may predict an arrhythmogenic focus of AF from SVC or RSPV.

Adrenergic beta-Agonists↗
PubMed2003

Clinical outcome of very late recurrence of atrial fibrillation after catheter ablation of paroxysmal atrial fibrillation.

INTRODUCTION: High recurrence rate is still a major problem associated with ablation of paroxysmal atrial fibrillation (AF). Most of the recurrences occur within 6 months after ablation. The characteristics of very late recurrent AF (>12 months after ablation) have not been reported. METHODS AND RESULTS: Two hundred seven patients with drug-refractory AF underwent successful focal ablation or isolation of AF foci. After the first ablation procedure, Holter monitoring and event recorders were used to evaluate symptomatic recurrent AF. A second ablation procedure was recommended if the antiarrhythmic drugs could not control recurrent AF. During long-term follow-up (mean 30 +/- 11 months, up to 51 months), 70 patients had recurrent AF, including 13 patients (6%) with very late (>12 months) recurrent AF (group 1) and 57 patients (28%) with late (within 12 months after ablation) recurrent AF (group 2). Group 1 patients had a significantly lower incidence of multiple (> or = 2) AF foci (23% vs 63%, P = 0.02) than group 2 patients. In addition, the incidence of antiarrhythmic drugs use (38% vs 84%, P = 0.001) to maintain sinus rhythm after the first episode of recurrent AF was significantly lower in group 1 than group 2 patients, and the incidence of a second intervention procedure (8% vs 35%, P = 0.051) tended to be lower in group 1 than group 2 patients. CONCLUSION: The incidence of very late recurrent AF after ablation of paroxysmal AF is very low, and the clinical outcome of patients with very late recurrent AF is benign.

Adult↗
PubMed2003

Spontaneous transition of 2:1 atrioventricular block to 1:1 atrioventricular conduction during atrioventricular nodal reentrant tachycardia: evidence supporting the intra-Hisian or infra-Hisian area as the site of block.

INTRODUCTION: The incidence of spontaneous transition of 2:1 AV block to 1:1 AV conduction during AV nodal reentrant tachycardia has not been well reported. Among previous studies, controversy also existed about the site of the 2:1 AV block during AV nodal reentrant tachycardia. METHODS AND RESULTS: In patients with 2:1 AV block during AV nodal reentrant tachycardia, the incidence of spontaneous transition of 2:1 AV block to 1:1 AV conduction and change of electrophysiologic properties during spontaneous transition were analyzed. Among the 20 patients with 2:1 AV block during AV nodal reentrant tachycardia, a His-bundle potential was absent in blocked beats during 2:1 AV block in 8 patients, and the maximal amplitude of the His-bundle potential in the blocked beats was the same as that in the conducted beats in 4 patients and was significantly smaller than that in the conducted beats in 8 patients (0.49 +/- 0.25 mV vs 0.16 +/- 0.07 mV, P = 0.007). Spontaneous transition of 2:1 AV block to 1:1 AV conduction occurred in 15 (75%) of 20 patients with 2:1 AV block during AV nodal reentrant tachycardia. Spontaneous transition of 2:1 AV block to 1:1 AV conduction was associated with transient right and/or left bundle branch block. The 1:1 AV conduction with transient bundle branch block was associated with significant His-ventricular (HV) interval prolongation (66 +/- 19 ms) compared with 2:1 AV block (44 +/- 6 ms, P < 0.01) and 1:1 AV conduction without bundle branch block (43 +/- 6 ms, P < 0.01). CONCLUSION: The 2:1 AV block during AV nodal reentrant tachycardia is functional; the level of block is demonstrated to be within or below the His bundle in a majority of patients with 2:1 AV block during AV nodal reentrant tachycardia, and a minority are possibly high in the junction between the AV node and His bundle.

Adult↗
PubMed2003

Pulmonary vein ablation: role in preventing atrial fibrillation.

Several investigators have identified the pulmonary vein as the most common initiator of atrial fibrillation, and isolation of the pulmonary vein from atrial tissue can cure approximately 70% of patients with paroxysmal atrial fibrillation. Ongoing trials of a new device may increase the success rate and decrease the complication rate during the pulmonary vein isolation procedure.

Animals↗