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Chu-Pak Lau

Publications and source records attributed to Chu-Pak Lau.

98 records · Page 6Linked to original sources
PubMed2002

Automatic mode switching of implantable pacemakers: II. Clinical performance of current algorithms and their programming.

While the hemodynamic and clinical significance of automatic mode switching (AMS) in patients with pacemakers has been demonstrated, the clinical behavior of AMS algorithms differ widely according to the manufacturers and pacemaker models. In general, a "rate-cutoff" detection method of atrial tachyarrhythmias provides a rapid AMS onset and resynchronization to sinus rhythm at the termination of atrial tachyarrhythmias, but may cause intermittent oscillations between the atrial tracking and AMS mode. This can be minimized with a "counter" of total number of high rate events before the AMS occurs. The use of a "running average" algorithm results in more stable rate control during AMS by reducing the incidence of oscillations, but at the expense of delayed AMS onset and resynchronization to sinus rhythm. Algorithms may be combined to fine tune the AMS response and to avoid rapid fluctuation in pacing rate. Appropriate programming of atrial sensitivity, and the avoidance of ventriculoatrial cross-talk are essential for optimal AMS performance.

Algorithms↗
PubMed2002

Bleeding and thromboembolic risks of internal cardioversion for persistent atrial fibrillation.

Although internal cardioversion is an effective method for converting AF the thromboembolic risk and bleeding complication of this procedure remains unclear. Retrospective analysis of the thromboembolic events and bleeding complications was performed in 114 consecutive patients (mean age 63 +/- 10 years, 91 men) who underwent internal cardioversion for persistent AF (mean AF duration 31 +/- 42 months). All patients received therapeutic warfarin for 3 weeks prior to the procedure, which was then replaced by periprocedural heparin therapy during internal cardioversion. The mean INR value before the internal cardioversion was 1.3 +/- 0.2. A total of 992 R wave synchronized shocks were delivered (mean 8.7 shocks/patients) without ventricular proarrhythmia. Successful internal cardioversion of AF was achieved in 100 (88%) patients. Two (2%) patients developed major bleeding complications with pericardial effusion after the procedure. Both of them subsided with conservative treatment. Minor bleeding with wound hematoma occurred in 8 (7%) of 114 after the procedure. Overall, there was no significant difference in the risk of procedure related complication between the use of heparin infusion and subcutaneous LMWH injection (6/78 [13%] vs 3/36 [8%], P = 0.9). No thromboembolic event was observed after 4 weeks of follow-up. In conclusion, the risk of thromboembolism after discontinuation of anticoagulation before the procedure is low in patients with persistent AF underwent internal cardioversion. However, the use of periprocedural heparin therapy was associated with an increase risk of procedure related bleeding complications.

Anticoagulants↗
PubMed2002

Effect of coexisting cardiovascular disease on the long-term efficacy and safety of the implantable atrial defibrillator.

The long-term efficacy and safety of implantable atrial defibrillator (IAD) therapy in patients with AF and cardiovascular disease is unclear. The aim of this study was to evaluate the efficacy and safety of IAD therapy in patients with and without coexisting cardiovascular disease. In 115 patients implanted with an IAD, 85 patients had cardiovascular disease: 41 (48%) patients had 1 cardiovascular abnormality, 29 (35%) patients had 2, 13 (15%) patients had 3, and 2 (2%) patients had 4 different cardiovascular abnormalities. The device was programmed into a rhythm monitoring mode for the first 3-month postimplant period. All defibrillation therapy was performed under physician supervision to monitor safety and efficacy. After this initial monitoring period, patients were allowed to activate their device away from the hospital or clinic. A total of 357 spontaneous AF episodes occurred in 83 (72%) patients during observed operation and the mean shock efficacy was 93.5+/-20.3% (lower 95% confidence interval [CI] 89.8%). As of the lastfollow-up, 58 (55%) patients had transition to receive nonphysician observed therapy. Forty-two (72%) patients had experienced 332 episodes of AF for which theyhad received device therapy away from the hospital/clinic (mean shock efficacy 90.5+/-39.7%). The presence of hypertension, valvular heart disease, and ischemic heart disease did not affect the shock efficacy of the IAD during physician observed and nonobserved therapy (P > 0.05). However, the presence of congestive heart failure was associated with a lower clinical efficacy during observed and nonobserved therapy (P < 0.05). Overall, 5,262 shocks have been delivered with the IAD without any episode of proarrhythmia. The observed proarrhythmic risk was 0%, with an estimated maximum proarrhythmic risk of 0.06% per shock (95% upper CI). A stand-alone IAD appears to be safe in the presence of cardiovascular disease. The lower clinical efficacy for AF associated with congestive heart failure might be related to a higher rate of early reinitiation of AF after defibrillation.

Adult↗
PubMed2002

Acute results of transvenous cryoablation of supraventricular tachycardia (atrial fibrillation, atrial flutter, Wolff-Parkinson-White syndrome, atrioventricular nodal reentry tachycardia).

INTRODUCTION: Radiofrequency (RF) catheter ablation currently is used for treatment of cardiac arrhythmias. Although the success rate is high for almost all supraventricular tachycardias (SVT), this technique has some drawbacks, especially when pulmonary veins (PV) are targeted for treatment of atrial fibrillation (AF). Additionally, new techniques for isolation of the PVs have the drawback that they can be used only for PV isolation and not for routine treatment of other SVTs. The aim of this study was to report on the safety and efficacy of a new cryoablation system for treatment of all SVTs. METHODS AND RESULTS: Forty-nine patients with SVT (38 men; age 48 years, range 23-76) were enrolled in the study. Five patients were withdrawn from the study before they underwent cryoablation. The remaining 44 patients were treated with cryoablation (22 AF, 15 atrial flutter, 3 accessory pathway, 2 AV nodal reentrant tachycardia, 1 AV junction ablation for permanent AF, 1 atrial tachycardia). Cryoablation was performed with the CryoCor cryoablation system, which uses a precooling system and N2O as a refrigerant. The number of freezes applied varied according to the index arrhythmia treated. Successful isolation of PVs was performed in 20 of (96%) 21 AF patients and 53 of 55 veins. The overall acute success was 98% (43/44). Fifty-three PVs were isolated (2.5/patient). The success rate was 100% (23/23) for right-sided procedures. The average and nadir temperatures reached in right-sided and left-sided procedures were -77 degrees C and -80 degrees C and -75 degrees C and -78 degrees C, respectively. No acute PV stenosis was seen. CONCLUSION: This novel cryoablation system appears to be safe and can successfully treat different types of SVTs, including AF. Isolation of PVs is possible without producing stenosis. Despite the high blood flow in the right atrial isthmus and PVs, bidirectional conduction block can be achieved.

Adult↗
PubMed2002

Transmural action potential and ionic current remodeling in ventricles of failing canine hearts.

Heart failure (HF) produces important alterations in currents underlying cardiac repolarization, but the transmural distribution of such changes is unknown. We therefore recorded action potentials and ionic currents in cells isolated from the endocardium, midmyocardium, and epicardium of the left ventricle from dogs with and without tachypacing-induced HF. HF greatly increased action potential duration (APD) but attenuated APD heterogeneity in the three regions. Early afterdepolarizations (EADs) were observed in all cell types of failing hearts but not in controls. Inward rectifier K(+) current (I(K1)) was homogeneously reduced by approximately 41% (at -60 mV) in the three cell types. Transient outward K(+) current (I(to1)) was decreased by 43-45% at +30 mV, and the slow component of the delayed rectifier K(+) current (I(Ks)) was significantly downregulated by 57%, 49%, and 58%, respectively, in epicardial, midmyocardial, and endocardial cells, whereas the rapid component of the delayed rectifier K(+) current was not altered. The results indicate that HF remodels electrophysiology in all layers of the left ventricle, and the downregulation of I(K1), I(to1), and I(Ks) increases APD and favors occurrence of EADs.

Action Potentials↗
PubMed2002

Stable and optimal anticoagulation is achieved with a single dose of intravenous enoxaparin in patients undergoing percutaneous coronary intervention.

This study assessed the pharmacokinetics, safety and efficacy of intravenous enoxaparin in patients undergoing percutaneous coronary intervention (PCI). Sixty consecutive patients [(age, 62 11 years; female, 16%; diabetes, 18%; hypertension, 53%; prior myocardial infarction (MI), 43%] undergoing PCI (stable angina, 89%; stent, 92%; two-vessel disease, 23%; B2/C lesions, 45%) were administered intravenous enoxaparin 1 mg/kg for procedural anticoagulation. Blood samples for anti-Xa level and activated partial thromboplastin time (aPTT) were assayed from the first 20 patients before and after enoxaparin administration at the following intervals: 5, 30, 60, 90, 120, 150, 180, 210, 240, 360 and 480 minutes. Activated clotting time was assessed 5 minutes after enoxaparin administration. Bleeding complications were classified according to Thrombolysis In Myocardial Infarction (TIMI) criteria. All patients were monitored for adverse clinical events at clinic visit 4 8 weeks after hospital discharge. No TIMI major or minor bleedings occurred during hospitalization for the PCI (median stay post-PCI = 1 day). One patient (2%) developed a non-Q wave MI after the PCI and before hospital discharge. There was no death or urgent revascularization up to clinical follow-up. The peak anti-Xa level was 1.30 0.18 IU/ml (range, 1.03 1.69 IU/ml). The minimum anti-Xa level was 0.55 IU/ml 4 hours after enoxaparin. Thus, the use of intravenous enoxaparin in patients undergoing PCI is associated with a low incidence of ischemic and bleeding complications. A stable therapeutic anticoagulant effect is provided without the need for monitoring within 4 hours of enoxaparin administration.

Aged↗
PubMedDate not supplied

Advantages of blood pressure optimization.

Lowering blood pressure (BP) reduces cardiovascular events, but aggressive BP management may not be advantageous. Optimal BP control (target: <120/80 mm Hg) and conventional BP control (target: <140/90 mm Hg) were compared in patients with hypertension in terms of target-organ damage and tolerability. A total of 23 patients with hypertension were randomly assigned to optimal versus conventional therapy for 6 months. Therapy was initiated with lercanidipine 10 mg/day. For BP control, the dose could be doubled or other drugs added. Three indices of target-organ damage were studied: left ventricular mass (LVM) index, flow-mediated dilatation (FMD) of the brachial artery, and 24-hour urinary albumin excretion. The BP decreased markedly by 21.3+/-3.4/13.2+/-1.7 mm Hg in the conventional therapy group and by 26.6+/-3.6/17.9+/-1.5 mm Hg in the optimal therapy group. Diastolic BP was significantly lower, by 4.7+/-2.3 mm Hg, in the optimal therapy group (P<.05). Ambulatory BP was also decreased in both groups. There was no significant change in LVM or FMD in either group. Baseline LVM index and FMD values were correlated with systolic BP (r=0.51, P=.02; r=0.54, P=.009). In the optimal therapy group, urinary albumin excretion increased significantly (P=.04). Plasma levels of B-type natriuretic peptide (BNP) decreased with antihypertensive therapy (P=.03). Treatment was well tolerated, and none of the patients withdrew from the study. There was no significant difference in adverse events between the 2 groups. Optimization of BP is feasible, safe, and well tolerated; however, a larger study of longer duration may be needed to demonstrate improvements in LVM and endothelial function with conventional versus optimal therapy.

Adolescent↗