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Biomedical subjects

Lai Chow Kok

Publications and source records attributed to Lai Chow Kok.

12 recordsLinked to original sources
PubMed2006

Right ventricular pacing to assess transisthmus conduction in patients undergoing isthmus-dependent atrial flutter ablation: a new useful technique?

BACKGROUND: Successful radiofrequency (RF) ablation of typical, isthmus-dependent atrial flutter requires establishment and confirmation of bidirectional conduction block across the cavotricuspid isthmus. Low atrial pacing usually is performed from the bipoles of the 20-pole Halo catheter, septal and lateral to the cavotricuspid isthmus ablation line. However, occasionally this is difficult because of high pacing thresholds and/or saturation of the atrial electrograms recorded near the pacing catheter. OBJECTIVES: The purpose of this study was to assess if right ventricular (RV) pacing and resulting retrograde atrial activation can be used to assess conduction block from the septum to the lateral wall in a clockwise direction. METHODS: Thirty-five consecutive male patients (mean age 64 +/- 10 years; mean ejection fraction 42 +/- 13%; mean left atrial dimension 44 +/- 6 mm) with typical isthmus-dependent atrial flutter were studied. The following electrophysiology catheters were used: 20-pole catheter along the tricuspid annulus, quadripolar catheters at the His and/or RV apex, and 8-mm ablation catheter. Following RF ablation of the cavotricuspid isthmus, bidirectional conduction block was confirmed in all 35 patients by pacing at a cycle length of 600 ms from bipoles septal and lateral to the cavotricuspid isthmus ablation line. Conduction times from pacing artifact to adjacent bipolar atrial electrograms and reversal of atrial activation pattern were analyzed. RV pacing was performed and retrograde atrial activation pattern assessed. If retrograde AV nodal conduction was absent, isoproterenol was infused intravenously at 2 microg/min, and RV pacing was repeated. The conduction time between the double potentials across the cavotricuspid isthmus ablation line was measured. RESULTS: Mean conduction times across the isthmus during septal (S), lateral (L), and RV pacing were 145 +/- 21 ms, 144 +/- 24 ms, and 129 +/- 20 ms, respectively. Retrograde AV nodal conduction was present in 34 of 35 patients (isoproterenol 8 patients). Evidence of conduction block by a clear change in activation pattern across the isthmus was seen during RV pacing in 33 of 35 patients with bidirectional conduction block. CONCLUSION: RV pacing is a simple and easy maneuver that can be performed to assess isthmus conduction in most patients.

Atrial Flutter↗
PubMed2005

Unusual variant of atrioventricular nodal reentrant tachycardia.

Electrophysiologic study in a patient with supraventricular tachycardia revealed an unusual activation pattern in the coronary sinus (CS) electrodes. Pacing maneuvers confirmed the tachycardia was a slow-slow AV nodal reentrant tachycardia with double potentials in the distal CS electrodes due to an earlier left atrial signal (50 ms) and later CS musculature activation. The left-sided AV nodal inputs were successfully ablated from within the CS.

Cardiac Pacing, Artificial↗
PubMed2005

Effect of short pulse width programming in AutoCapture devices.

Pacing chronaxie can increase over time. The impact of a short pulse duration on threshold (THR) variations, frequency of noncapture episodes, and overall patient safety has not been fully studied. AutoCapture (AC) pacemakers are capable of memorizing THR trends and loss of capture (LOC) episodes. The study included 20 recipients of AC pacemakers (mean age = 76 +/- 9 years, 15 men) followed for 6 months. They were randomly assigned to pulse durations of 0.2 versus 1.0 ms at 1 month, and crossed over to the alternate programming at 3 months. Evoked response (ER) and AC tests were performed at follow-up. At 0.2 ms and 1.0 ms, the mean number of LOC/day was 2.37 +/- 5.81 and 0.91 +/- 0.49, respectively (ns). LOC trends between follow-up were significantly different with 0.2 versus 1.0 ms pulse duration (P < 0.01). AC THR at 1.0 ms was significantly lower (0.44 +/- 0.77) than at 2.0 ms (0.97 +/- 0.26, P < 0.05). No patient reported symptoms related to LOC during the study. Pulse duration programmed near the strength-duration curve is associated with greater variations in THR and LOC. AC responds to these changes by delivering 4.5 V pulses and keeping the capture THR at low, though safe values.

Aged↗
PubMed2004

Device therapy for atrial fibrillation.

Currently, there are more therapeutic options available for AF patients with recurrent symptomatic AF episodes. The studies on the role of device therapy for AF have been promising thus far, but they have not achieved any of the goals of AF management. Based on large randomized clinical trials, patients with SSS should receive atrial-based pacing devices. Moderate sized randomized studies have shown minimal benefit of multi-site pacing in AF prevention, even when combined with antiarrhythmic agents. Alternative site pacing such as septal pacing (high or low), however, may be more advantageous, as it achieves similar results in terms of AF reduction with less hardware. The role of ATP in AF prevention is still in its infancy and will need further studies to determine its role in conjunction with antiarrhythmic agents. Furthermore, the role of radiofrequency ablation of pulmonary veins and other sites of AF initiation has been evolving and may be offered to more patients in the future. This approach may be more acceptable to patients and may gain wider acceptance for some groups of AF patients rather than device therapy. In any event, there is still a large role for pacemaker therapy in the management of AF, especially in patients who cannot benefit from curative ablation or surgery procedures, or patients who have failed these procedures, and particularly elderly patients who typically do not undergo these procedures. Based on current understanding, careful selection of pacing sites and pacing algorithms may help in reducing AF episodes in patients receiving devices.

Atrial Fibrillation↗
PubMed2004

Response of pulmonary vein potentials to burst pacing.

BACKGROUND: Pulmonary vein potentials recorded at the ostia of pulmonary veins (PV) are a useful guide for segmental isolation of the PV in patients with atrial fibrillation (AF). Even during coronary sinus pacing at 600 ms, atrial (A) and PV potentials can overlap in 50-60% of patients making the accurate identification of PV potentials very difficult. METHODS: Nineteen patients (M:F 15:4) with paroxysmal AF underwent segmental isolation of one or more PV. Coronary sinus (CS) pacing was performed at cycle lengths of 600/550/500/450/400/350/300 ms and bipolar electrograms were recorded from the 10 or 20 pole Lasso catheter placed at the atrial-PV junction in 27 pulmonary veins. Stimulus (S) to A, S-PVP and A-PVP intervals were measured during CS pacing at the different cycle lengths at sweep speed of 200 mm/sec. RESULTS: During CS pacing at 600 ms the A and PV potentials were significantly overlapped (A-PVP < or = 25 ms) in 15 of 27 (55%) veins. During pacing at 300 ms, the A and PV potentials were significantly separated (A-PVP > or = 25 ms) in 9 of the 15 veins where A and PV potentials overlapped and 21 of all 27 (78%) veins. In two patients pacing at 300 ms was associated with 2:1 conduction block from atrial to PV fascicle. CONCLUSIONS: Coronary sinus pacing at cycle length of 300 ms demonstrated better separation of A and PV potentials compared to pacing at 600 ms. This strategy is easier and less time consuming compared to extrastimuli testing. It also confirms that the electrophysiological properties of PV fascicles are different from that of the adjacent atrial musculature.

Atrial Fibrillation↗
PubMed2003

Effect of heating on pulmonary veins: how to avoid pulmonary vein stenosis.

INTRODUCTION: The success of radiofrequency energy catheter ablation for the treatment of patients with paroxysmal or chronic atrial fibrillation has been complicated by postablation development of pulmonary vein (PV) stenosis. The acute effect of heat on PV structure has not been well characterized. The aim of this study was to characterize the effects of hyperthermic exposure on PVs and to determine the critical temperature at which PV stenosis would be observed. METHODS AND RESULTS: The main PVs of acutely explanted canine hearts were identified, isolated, and dissected from the left atria. Measurements of the diameter of 3-mm PV rings were obtained at baseline and after hyperthermic exposure at 60 degrees C, 65 degrees C, 70 degrees C, and 80 degrees C. Mechanical behavior of PVs was studied by examining the stress-strain relationship of each PV specimen after heat exposure at different temperature settings. Twenty-eight PVs samples from 15 dogs (1-3 PVs/dog) were obtained and had a mean circumference of 8.7 +/- 2.3 mm at baseline. After heating to 60 degrees C, 65 degrees C, 70 degrees C, and 80 degrees C, the mean PV circumference was 9.2 +/- 2.3 mm (P = NS vs baseline), 6.8 +/- 2.3 mm (P < 0.0001), 4.2 +/- 1.5 mm (P < 0.0001), and 4.2 +/- 0.8 mm (P < 0.0001), respectively. The stress-strain curves of PV specimens were shifted to the left upon exposure to higher temperatures, indicating loss of compliance of PVs due to heat exposure. Histology showed loss of typical collagen matrix above 60 degrees C. CONCLUSION: Significant acute heat-induced contraction of PVs at zero-tension state was observed between 60 degrees C and 65 degrees C. This change was associated with collagen denaturation.

Animals↗
PubMed2002

Intracardiac echocardiography-guided, anatomically based radiofrequency ablation of focal atrial fibrillation originating from pulmonary veins.

OBJECTIVES: In patients with a pulmonary vein (PV) source for atrial fibrillation (AF), we sought the use of intracardiac echocardiography (ICE) to evaluate PV anatomy, guide radiofrequency (RF) ablation and monitor for acute stenosis during ablation. BACKGROUND: A focal source for AF may be found in the proximal component of the PVs and can be effectively treated by ablative techniques. However, the procedure may be challenging due to the complex anatomy of the left atrium and PVs, uncertain catheter positioning within the PVs and difficulties in mapping atrial extrasystoles, which may be rare or repeatedly induce AF and require cardioversion. METHODS: Sixty-four patients were referred for RF ablation of a focal source of AF, and 56 were identified as having AF triggers in > or =1 PV. Using ICE guidance, RF lesions were applied around the circumference of the vein near the os until there was electrical isolation. RESULTS: Lesions were placed in 82 veins (36 right superior PV, 33 left superior PV, 9 left inferior PV, 4 right inferior PV); 24 +/- 12 lesions per vein were necessary to create electrical isolation with a fluoroscopic time of 11 +/- 4 min and a mean of 22% reduction in luminal area. After a follow-up of 13 +/- 7 months, 66% of patients remained free of AF, and another 13% responded better to medications. CONCLUSIONS: We describe an anatomic approach to PV electrical isolation in which ICE is used to define the anatomy, guide RF ablation and monitor for acute PV changes.

Atrial Fibrillation↗
PubMed2002

Cerebrovascular complication associated with pulmonary vein ablation.

INTRODUCTION: Radiofrequency (RF) ablation has become an established treatment modality for patients with paroxysmal atrial fibrillation (AF). A principal limitation of RF catheter ablation is the risk of thromboembolism. Stroke as a complication after ablation of triggers of AF has not been previously reported. METHODS AND RESULTS: Fifty-six patients underwent RF ablation for a focal source of AF. Forty-nine patients (86%) had AF triggers in > or = 1 pulmonary vein. Mean procedure time was 227 +/- 74 minutes. Cerebrovascular event occurred in 3 (5%) patients, all >60 years old. Two of the three patients had a prior history of transient ischemic attacks. CONCLUSION: The risk of stroke from RF ablation may be higher in paroxysmal AF patients with prior transient ischemic attack.

Adult↗