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Chu-Pak Lau

Publications and source records attributed to Chu-Pak Lau.

At least 37 records · Page 2Linked to original sources
PubMed2006

Prediction of aortic augmentation index using radial pulse transmission-wave analysis.

OBJECTIVE: Current arterial transfer functions have low capability in predicting aortic augmentation index (AIx) from radial pulse contour (RPC), because of the difficulty in accurately identifying the merging point (inflection point) in the derived aortic pulse contour (APC). We hypothesize that the formation time between each characteristic wave in APC is about one-third of ejection duration (ED/3). We sought to assess the accuracy of ED/3 in identifying the merging point in APC as compared to the conventional differential method. In addition, we sought to derive the AIx from RPC based on an arterial transfer function and the ED/3 method. METHODS: APC and RPC sequences were measured digitally and simultaneously in 60 subjects (37 males; aged 60 +/- 10 years). An ensemble-averaged RPC-to-APC transfer function was determined from 30 randomly selected subjects and was used to derive APC sequences in the 30 additional subjects. The accuracy of AIx predicted from RPC was determined. RESULTS: In patients with a clearly identifiable merging point in APC, the ED/3 method identified the merging point of measured APC within 1.97 +/- 0.60 ms of that identified by the conventional differential method, with identical AIx. The AIx and merging point of derived APC using the ED/3 method were also within 0.22 +/- 1.01% and 1.81 +/- 1.64 ms, respectively, of those of the measured APC using the conventional differential method. The accuracy of the predicted AIx was independent of age, sex, body-mass index and presence of hypertension. CONCLUSION: In a quiet resting state, the ED/3 is an alternative method for identifying the merging point in APC. In conjunction with transfer-function technique, AIx can be derived accurately from RPC.

Adult↗
PubMed2006

Prevalence, awareness, treatment, and control of hypertension: United States National Health and Nutrition Examination Survey 2001-2002.

The prevalence, awareness, treatment, and control of hypertension in the United States are analyzed using the National Health and Nutrition Examination Survey (NHANES) database covering the period 1988-2002. Mean body mass index was 26.1+/-0.1 kg/m2 in 1988-1991 and 27.9+/-0.2 kg/m2 in 2001-2002 (p < 0.001). In the same period, the prevalence of diabetes mellitus increased from 5.0% to 6.5% (p = 0.03). Diastolic blood pressure was 73.3+/-0.2 mm Hg in 1988-1991 and 71.6+/-0.4 mm Hg in 2001-2002 (p < 0.001). Among the 18-39 years and 60 years and older age groups, the prevalence of hypertension increased significantly since 1988-1991. Multiple regression shows age, body mass index, and being non-Hispanic black were significantly associated with hypertension. In the period 1988-2002, the percentage receiving treatment and the percentage with blood pressure controlled increased significantly. In 2001-2002, significantly more people with hypertension and diabetes reached a blood pressure target of <130/85 mm Hg. Overall, the control rates were low, especially among middle-aged Mexican-American men (8%).

Adolescent↗
PubMed2006

Prevalence of the metabolic syndrome in the United States National Health and Nutrition Examination Survey 1999-2002 according to different defining criteria.

The authors studied the prevalence of the metabolic syndrome in the 1999-2002 National Health and Nutrition Examination Survey (NHANES) according to the World Health Organization, National Cholesterol Education Program (NCEP), and International Diabetes Federation (IDF) definitions. There was 92.9% agreement between the NCEP and IDF definitions. The IDF prevalence was higher (p = 0.001) due to more men fulfilling its criteria than the NCEP's (39.9 +/- 1.7% vs. 33.6 +/- 1.6%; p = 0.007). If central obesity were not a prerequisite, the IDF prevalence would increase slightly to 40.3 +/- 1.1%. Subjects categorized as having the metabolic syndrome under IDF but not NCEP tended to be men, younger, and leaner. Their prevalence of self-reported coronary heart disease was not significantly different from that of other metabolic syndrome patients. Whether waist circumference is a prerequisite does not affect the diagnosis of the metabolic syndrome in the United States. The IDF definition identifies additional individuals at risk for cardiovascular disease.

Adult↗
PubMed2006

Endocardial visualization of esophageal-left atrial anatomic relationship by three-dimensional multidetector computed tomography "navigator imaging".

BACKGROUND: The close proximity of left atrium (LA) and esophagus during radiofrequency ablation for atrial fibrillation (AF) predisposes to thermal injury resulting in atrio-esophageal fistula. This work proposes to study the anatomic relationship between the esophagus and the LA wall using multidetector computed tomography (MDCT) three-dimensional (3D) "Navigator" reconstruction technique. METHODS: Forty-five consecutive patients (37 men, mean age 52.7+/-14.1 years) with preradiofrequency ablation MDCT scans of the thorax for AF were recruited. Length and type (continuous or interrupted) of fat pad between esophagus and LA were evaluated. The position, width, and length of the esophagus in contact (without fat pad) with the LA were determined by using "Navigator" software on the endocardial view of LA. RESULTS: The fat pad was continuous in 4% (2 of 45) and interrupted in 96% (43 of 45) patients. The mean width and length of esophageal-LA contact in 43 cases with interrupted fat pad was 24.0+/-5.8 mm (range 10.5-35.3 mm) and 41.9+/-11.6 mm (5.4-64 mm), respectively. There was an inverse relationship between the lengths of the esophageal-LA contact and the upper fat pad (r=-0.50, P=0.001). The esophagus was located to the left, right, and midline of the LA in 40, 2, and 1 patients, respectively, and the esophagus was in contact with and overrode the PV orifice in 22 and 4 patients, respectively. CONCLUSION: Direct esophageal-LA contact without the intervening fat pad was present in 96% of the cases, with 93% of esophagi lying to the left of the LA and 51% in contact with a PV orifice. Three-dimensional Navigator imaging technique has enhanced the visualization of the anatomical information of the esophagus, LA wall, and PV orifices that may be used to avoid thermal injury to the esophagus during LA ablation procedure.

Adult↗
PubMed2006

Avoidance of electromagnetic interference to implantable cardiovertor-defibrillator during atrioventricular node ablation for atrial fibrillation using transvenous cryoablation.

Transient or permanent malfunction of implantable device may result from electromagnetic interference during delivery of radiofrequency energy for treatment of cardiac arrhythmias. Therefore, there is a clinical need for an alternative energy source for cardiac arrhythmia ablation in patients with implantable device. This report presents a case of the absence of electromagnetic interference to an implantable cardioverter defibrillator during atrioventricular nodal ablation for atrial fibrillation to avoid inappropriate shock.

Aged↗
PubMed2005

The incremental benefit of rate-adaptive pacing on exercise performance during cardiac resynchronization therapy.

OBJECTIVES: The purpose of this research was to investigate the effect of using rate-adaptive pacing and atrioventricular interval (AVI) adaptation on exercise performance during cardiac resynchronization therapy (CRT). BACKGROUND: The potential incremental benefits of using rate-adaptive pacing and AVI adaptation with CRT during exercise have not been studied. METHODS: We studied 20 patients with heart failure, chronotropic incompetence (<85% age-predicted heart rate [AP-HR] and <80% HR reserve), and implanted with CRT. All patients underwent a cardiopulmonary exercise treadmill test using DDD mode with fixed AVI (DDD-OFF), DDD mode with adaptive AVI on (DDD-ON), and DDDR mode with adaptive AVI on (DDDR-ON) to measure metabolic equivalents (METs) and peak oxygen consumption (VO2max). RESULTS: During DDD-OFF mode, not all patients reached 85% AP-HR during exercise, and 55% of patients had <70% AP-HR. Compared to patients with >70% AP-HR, patients with <70% AP-HR had significantly lower baseline HR (66 +/- 3 beats/min vs. 80 +/- 5 beats/min, p = 0.015) and percentage HR reserve (27 +/- 5% vs. 48 +/- 6%, p = 0.006). In patients with <70% AP-HR, DDDR-ON mode increased peak exercise HR, exercise time, METs, and VO2max compared with DDD-OFF and DDD-ON modes (p < 0.05), without a significant difference between DDD-OFF and DDD-ON modes. In contrast, there were no significant differences in peak exercise HR, exercise time, METs, and VO2max among the three pacing modes in patients with >70% AP-HR. The percentage HR changes during exercise positively correlated with exercise time (r = 0.67, p < 0.001), METs (r = 0.56, p < 0.001), and VO2max (r = 0.55, p < 0.001). CONCLUSIONS: In heart failure patients with severe chronotropic incompetence as defined by failure to achieve >70% AP-HR, appropriate use of rate-adaptive pacing with CRT provides incremental benefit on exercise capacity during exercise.

Adaptation, Physiological↗
PubMed2005

Mast cell contributes to cardiomyocyte apoptosis after coronary microembolization.

Coronary microembolization (CME) is associated with progressive myocardial dysfunction despite restoration of coronary flow reserve (CFR). The potential pathophysiological role of mast cells (MCs) remains unclear. Therefore, we induced CME in 18 miniswines and determined whether MC accumulation occurs and their effects on local cytokine secretion [interleukin (IL)-6, IL-8, tumor necrosis factor-alpha (TNF-alpha)]; cardiomyocyte apoptosis; and collagen formation at day 1 (D1), day 7 (D7), and day 30 (D30) after CME. Four sham-operated animals without CME (controls) and six animals treated with a MC stabilization agent (tranilast) for 30 days after CME were also studied. CFR decreased at D1 but returned to baseline level at D7 and D30. Coronary sinus levels of IL-6, IL-8, and TNF-alpha increased significantly at D1 and D7 (p<0.01 vs baseline). Levels of IL-6 and IL-8 at D30 returned to baseline level, but not those of TNF-alpha. The numbers of total and degranulating MCs, % apoptotic cardiomyocytes, and collagen volume fraction (CVF) over CME myocardium at D1, D7, and D30 were significantly higher than controls (p<0.01). Treatment with tranilast significantly reduced the serum level of TNF-alpha, numbers of total and degranulating MCs, % apoptotic cardiomyocytes, and CVF at D30 (all p<0.05). There was a significant positive correlation between the numbers of MCs with % apoptotic cardiomyocytes (r = 0.77, p<0.001) and CVF (r = 0.75, p<0.001) over the CME myocardium. Despite restoration of CFR, cardiomyocyte apoptosis persisted after CME and was positively correlated with the number of MCs but was prevented with tranilast treatment. These findings suggest that MCs contribute to cardiomyocyte apoptosis after CME.

Animals↗
PubMed2005

Relation of aspirin resistance to coronary flow reserve in patients undergoing elective percutaneous coronary intervention.

Previous studies have shown that more complete platelet inhibition improves the coronary flow reserve (CFR), a measure of microvascular integrity, in patients undergoing percutaneous coronary intervention (PCI). We hypothesized that patients with aspirin resistance would have impaired CFR after elective PCI. We used VerifyNow Aspirin to determine the response to aspirin in 117 consecutive patients who underwent elective single-lesion PCI. The assay results are expressed quantitatively in Aspirin Reaction Units based on the degree of platelet aggregation. All patients received a 300-mg loading dose of clopidogrel >12 hours before and a 75-mg maintenance dose the morning of PCI. CFR was estimated using the Thrombolysis In Myocardial Infarction frame count method. Of the 117 patients, 22 (18.8%) were aspirin resistant. The clinical, angiographic, and procedural characteristics of the aspirin-sensitive and -resistant patients were balanced. All patients underwent successful PCI with <50% residual diameter stenosis and Thrombolysis In Myocardial Infarction grade 3 flow after PCI. Aspirin-resistant patients had a lower CFR than the aspirin-sensitive patients (1.42 +/- 0.35 vs 1.80 +/- 0.64, p = 0.018). Univariate correlates of CFR included the Aspirin Reaction Unit (r = -0.227, p = 0.014) and post-PCI creatine kinase-MB elevation (p = 0.048). Multivariate linear regression analysis revealed the Aspirin Reaction Unit to be the only independent determinant of CFR after PCI (r2 = 0.051, p = 0.014). Thus, aspirin resistance was associated with impaired CFR in patients who underwent elective PCI, implicating insufficient aspirin-induced platelet inhibition as a cause of microvascular dysfunction by distal atherothrombotic embolization and/or spasm.

Aged↗
PubMed2005

Electrophysiological properties of pluripotent human and mouse embryonic stem cells.

Pluripotent embryonic stem cells (ESCs) possess promising potential for cell-based therapies, but their electrophysiological properties have not been characterized. Here we describe the presence of ionic currents in mouse (m) and human (h) ESCs and their physiological function. In mESCs, tetraethylammonium (TEA)-sensitive depolarization-activated delayed rectifier K+ currents (IK(DR)) (8.6 +/- 0.9 pA/pF at +40 mV; IC50 = 1.2 +/- 0.3 mM), which contained components sensitive to 4-aminopyridine (4-AP) (IC50 = 0.5 +/- 0.1 mM) and 100 nM Ca2+-activated K+ current (IK(Ca)) blocker iberiotoxin (IBTX),were detected in 52.3% of undifferentiated cells.IK(DR) was similarly present in hESCs (approximately 100%) but with an approximately sixfold higher current density (47.5 +/- 7.9 pA/pF at +40 mV). When assayed by bromodeoxyurindine incorporation, application of TEA, 4-AP, or IBTX significantly reduced the proliferation of mESCs and hESCs in a dose-dependent manner (p < .05). A hyperpolarization-activated inward current (I(h)) (-2.2 +/- 0.4 pA/pF at -120 mV) was detected in 23% of mESCs but not hESCs. Neither Na(v) nor Ca(v) currents were detected in mESCs and hESCs. Microarray and reverse transcription-polymerase chain reaction analyses identified several candidate genes for the ionic currents discovered. Collectively, our results indicate that pluripotent ESCs functionally express several specialized ion channels and further highlight similarities and differences between the two species. Practical considerations for the therapeutic use of ESCs are discussed.

4-Aminopyridine↗
PubMed2005

Intrathoracic impedance monitoring in patients with heart failure: correlation with fluid status and feasibility of early warning preceding hospitalization.

BACKGROUND: Patients with heart failure are frequently hospitalized for fluid overload. A reliable method for chronic monitoring of fluid status is therefore desirable. We evaluated an implantable system capable of measuring intrathoracic impedance to identify potential fluid overload before heart failure hospitalization and to determine the correlation between intrathoracic impedance and standard measures of fluid status during hospitalization. METHODS AND RESULTS: Thirty-three patients with NYHA class III and IV heart failure were implanted with a special pacemaker in the left pectoral region and a defibrillation lead in the right ventricle. Intrathoracic impedance was regularly measured and recorded between the lead and the pacemaker case. During hospitalizations, pulmonary capillary wedge pressure and fluid status were monitored. Ten patients were hospitalized for fluid overload 25 times over 20.7+/-8.4 months. Intrathoracic impedance decreased before each admission by an average of 12.3+/-5.3% (P<0.001) over an average of 18.3+/-10.1 days. Impedance reduction began 15.3+/-10.6 days (P<0.001) before the onset of worsening symptoms. There was an inverse correlation between intrathoracic impedance and pulmonary capillary wedge pressure (r=-0.61, P<0.001) and between intrathoracic impedance and net fluid loss (r=-0.70, P<0.001) during hospitalization. Automated detection of impedance decreases was 76.9% sensitive in detecting hospitalization for fluid overload, with 1.5 false-positive (threshold crossing without hospitalization) detections per patient-year of follow-up. CONCLUSIONS: Intrathoracic impedance is inversely correlated with pulmonary capillary wedge pressure and fluid balance and decreased before the onset of patient symptoms and before hospital admission for fluid overload. Regular monitoring of impedance may provide early warning of impending decompensation and diagnostic information for titration of medication.

Aged↗
PubMed2005

Smoking, homocysteine and degree of arteriolar retinopathy.

It has been demonstrated that higher degree of arteriolar retinopathy is associated with greater cardiovascular risk, and hyperhomocysteinaemia is also related to increased cardiovascular risk, but interacts with other risk factors, particularly smoking. It still remains unclear regarding relationships of smoking, fasting plasma total homocysteine (tHcy) levels and arteriolar retinopathy. This study was aimed to investigate the relationship and influence of smoking and tHcy levels on degree of arteriolar retinopathy. Two hundred and forty-three subjects were enrolled from an annual health examination. The arteriolar retinopathy was examined by direct ophthalmoscopy. Dundett ANOVA showed that geometric mean of tHcy levels were 11.5+/-1.54 versus 11.2+/-1.41 versus 17.6+/-1.92 (P1=0.883, P2=0.001) in subjects with no arteriolar retinopathy (as control group), grades I and II retinopathy, respectively. Furthermore, multiple linear regression analysis showed that only smoking consumption (P<0.001), gender (P=0.012) and presence of hypertension (P=0.041) were independent determinants of plasma tHcy levels. After females were excluded, T-test showed a significant differences in tHcy levels (15.6+/-1.56 micromol/L versus 12.4+/-1.45 micromol/L, P=0.003) and in prevalence of grade II retinopathy (25.4% versus 9.3%, P=0.029), but no difference in other variables or prevalence of overall retinopathy between smokers and non-smokers. Finally, logistic regression showed that smoking (OR 4.19, 95% CI 1.17-15.0) was a stronger predictor than hyperhomocysteinaemia (OR 2.14, 95% CI 0.85-5.41) for presence of grade II retinopathy. This study showed that smoking was related to increased plasma tHcy levels in subjects with grade II retinopathy, and it could independently contribute to facilitating the progression of arteriolar retinopathy.

Adult↗
PubMed2005

Inappropriate implantable cardioverter defibrillator shock from a transcutaneous muscle stimulation device therapy.

Inappropriate shock from implantable cardioverter defibrillator (ICD) may result from external electromagnetic interference (EMI), especially for unipolar ventricle sensing. Previous case reports and small in-vitro safety study suggested that endocardial bipolar lead system may be immune from EMI resulting from transcutaneous electrical neuromuscle stimulation (TENS) therapy. This report presents an unusual case of inappropriate discharge in a patient with ICD of endocardial bipolar lead system, receiving TENS from a commercially available device.

Aged↗
PubMed2005

Low-dose aspirin increases aspirin resistance in patients with coronary artery disease.

PURPOSE: We sought to investigate the association of aspirin dose and aspirin resistance in stable coronary artery disease patients measured by a point-of-care assay. METHODS: We studied 468 consecutive stable coronary artery disease patients in a referral cardiac center who were taking aspirin 80 to 325 mg daily for > or =4 weeks. The VerifyNow Aspirin (Ultegra RPFA-ASA, Accumetrics Inc, San Diego, Calif) was used to determine aspirin responsiveness. An aspirin reaction unit (ARU) > or =550 indicates the absence of aspirin-induced platelet dysfunction, based on correlation with epinephrine-induced light transmission aggregometry. Demographic and clinical data were collected to analyze the predictors of aspirin resistance. RESULTS: Aspirin resistance was noted in 128 (27.4%) patients. Univariate predictors of aspirin resistance include elderly (P = 0.002), women (P <0.001), anemia (P <0.001), renal insufficiency (P = 0.009) and aspirin dose < or =100 mg (P = 0.004). Multivariate analysis revealed hemoglobin (odds ratio [OR] 0.6; 95% confidence interval [CI] 0.51 to 0.69; P <0.001) and aspirin dose < or =100 mg (OR 2.23; 95% CI 1.12 to 4.44; P = 0.022) to be independent predictors of aspirin resistance. Daily aspirin dose < or = 100 mg was associated with increased prevalence of aspirin resistance compared with 150 mg and 300 mg daily (30.2% vs 16.7% vs 0%, P = 0.0062). CONCLUSION: A 100 mg or less daily dose of aspirin, which may have lower side effects, is associated with a higher incidence of aspirin resistance in patients with coronary artery disease. Prospective randomized studies are warranted to elucidate the optimal aspirin dosage for preventing ischemic complications of atherothrombotic disease.

Aged↗
PubMed2005

Effects of diltiazem and nifedipine on transient outward and ultra-rapid delayed rectifier potassium currents in human atrial myocytes.

1. It is unknown whether the widely used L-type Ca(2+) channel antagonists diltiazem and nifedipine would block the repolarization K(+) currents, transient outward current (I(to1)) and ultra-rapid delayed rectifier K(+) current (I(Kur)), in human atrium. The present study was to determine the effects of diltiazem and nifedipine on I(to1) and I(Kur) in human atrial myocytes with whole-cell patch-clamp technique. 2. It was found that diltiazem substantially inhibited I(to1) in a concentration-dependent manner, with an IC(50) of 29.2+/-2.4 microM, and nifedipine showed a similar effect (IC(50)=26.8+/-2.1 muM). The two drugs had no effect on voltage-dependent kinetics of the current; however, they accelerated I(to1) inactivation significantly, suggesting an open channel block. 3. In addition, diltiazem and nifedipine suppressed I(Kur) in a concentration-dependent manner (at +50 mV, IC(50)=11.2+/-0.9 and 8.2+/-0.8 microM, respectively). These results indicate that the Ca(2+) channel blockers diltiazem and nifedipine substantially inhibit I(to1) and I(Kur) in human atrial myocytes.

Calcium Channel Blockers↗
PubMed2005

Effects of temporal application parameters on lesion dimensions during transvenous catheter cryoablation.

UNLABELLED: Lesion dimension of cryoablation. BACKGROUND: Transvenous catheter cryoablation is a novel technique for treating cardiac arrhythmias. However, the relative importance of temporal application parameters on lesion dimension and clinical efficacy has not been studied. METHODS AND RESULTS: We investigated the effects of (1) application duration: single 2.5 (2.5x1) versus single 5 versus double 2.5 (2.5x2) versus double 5 (5x2) minutes, (2) number of freeze-thaw cycles: single versus double, and (3) electrode contact area: horizontal versus vertical orientation, on the lesion diameter and depth during catheter cryoablation (10F, 6.5-mm tip-electrode, CryoCor, San Diego) in a thigh muscle preparation. A total of 175 lesions (horizontal=90, vertical=85) were created in thigh muscle preparations on 10 swine. The lesion diameter and depth were significantly greater using 2.5x2 and 5x2 application modes as compared with 2.5x1 applications (P<0.05). Horizontal tip-electrode orientation produced larger lesion diameter (P<0.05), but not lesion depth as compared with vertical orientation. Multivariate analysis demonstrated that both tip-electrode orientation and duration of freeze >2.5 minutes were independent predictors for lesion diameter (P<0.001). However, only duration of freeze >2.5 minutes was an independent predictor for lesion depth (P<0.001). CONCLUSIONS: The dimensions of lesions created by catheter cryoablation are affected by mode of cryoablation application and electrode orientation. Increasing the duration of application, employing multiple freeze-thaw cycles at shorter cycle durations, and orienting the catheter to enhance/increase tissue contact can create a larger lesion.

Animals↗