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Biomedical subjects

C P Lau

Publications and source records attributed to C P Lau.

At least 19 recordsLinked to original sources
PubMed1992

Cardiotoxicity after accidental herb-induced aconite poisoning.

Aconitine and its related alkaloids are known cardiotoxins with no therapeutic role in modern western medicine. The rootstocks of Aconitum plants, which contain aconite alkaloids, have been common components of Chinese herbal recipes. We have documented life-threatening intoxication in 17 Chinese subjects after accidental herb-induced aconite poisoning. All patients developed symptoms of aconite toxicity within 2 h of herb ingestion. Most developed tachyarrhythmias, including ventricular tachycardia and fibrillation from which 2 patients died. Toxicological evaluation revealed that aconites from the Aconitum rootstocks were the only plausible casual factor for intoxication. These cases point to the need for strict surveillance of herbal substances with low safety margins.

Accidents↗
PubMed1992

Percutaneous transluminal coronary angioplasty in a patient with paroxysmal nocturnal hemoglobinuria.

Paroxysmal nocturnal hemoglobinuria (PHN) is an acquired chronic hemolytic anemia associated with an unusual susceptibility to hemolytic crisis, infection, and venous thrombosis which would be aggravated by a number of factors including surgery. We report a case of PHN undergoing percutaneous transluminal coronary angioplasty and discuss the corresponding perioperative management.

Adult↗
PubMed1992

Successful sequential radiofrequency catheter ablation of anatomically discrete antegrade and retrograde accessory pathway conduction in the Wolff-Parkinson-White syndrome.

Histopathologically, accessory atrioventricular (AV) pathways comprise tiny strands of working myocardium that traverse the AV groove and link between the atrial and ventricular myocardium. Antegrade and retrograde conduction in bidirectional accessory pathways have generally been considered to occur along the same fibers. This report details the successful catheter ablation of a left free wall accessory pathway with radiofrequency energy. Antegrade and retrograde conduction of the pathway were abolished sequentially by separate episodes of energy delivered at anatomically discrete though closely adjacent sites along the mitral annulus. This finding raises the interesting possibility of anatomic "compartmentalization" of antegrade and retrograde conduction along an accessory pathway.

Adult↗
PubMed1992

Acute hemorrhagic myocarditis in systemic lupus erythematosus.

We report a 46-year-old patient with longstanding systemic lupus erythematosus (SLE) who developed rapidly progressive heart failure and died. At postmortem, there was a unique picture of hemorrhage and mild inflammation present in the myocardium causing the heart failure. As far as we are aware, this picture has not been described before in SLE and is similar to that seen in the cardiac allograft hyperacute rejection.

Coronary Vessels↗
PubMed1992

A randomized double-blind crossover study comparing the efficacy and tolerability of flecainide and quinidine in the control of patients with symptomatic paroxysmal atrial fibrillation.

Patients with paroxysmal atrial fibrillation (PAF) are prone to recurrence. We compared the efficacy and tolerability of flecainide acetate in the control of PAF by means of conventional treatment with quinidine in 19 patients without structural heart disease. A randomized, placebo-controlled, crossover protocol consisting of 8 weeks of treatment with either agent was used. The recurrence of PAF was documented in a symptom diary and confirmed by event ECG recording. Complete control of symptoms was achieved in 4 of 19 and 2 of 11 of patients with flecainide and quinidine, respectively. Both agents prolonged the time to the first recurrence and significantly reduced the total duration of PAF recurrence by 40% and 47%, respectively (p less than 0.05 compared with placebo). Compared with quinidine, flecainide significantly reduced the frequency of recurrence and the rate of PAF during a recurrent episode. However, treatment with flecainide was associated with a higher incidence of symptomatic sinus pauses and visual disturbances compared with a higher incidence of gastrointestinal side effects with quinidine. During a follow-up period of 32 months, satisfactory control was achieved in 74% of patients with the use of these two antiarrhythmic agents.

Adult↗
PubMed1992

Effects of severity of the residual stenosis of the infarct-related coronary artery on left ventricular dilation and function after acute myocardial infarction.

OBJECTIVES: This study was designed to evaluate the relation between the severity of the residual stenosis of the infarct-related artery and changes in left ventricular volume and function after a first anterior myocardial infarction. BACKGROUND: Although thrombolytic therapy improves clinical outcome after acute myocardial infarction, the relations between the severity of the residual stenosis of the infarct-related artery and postinfarction left ventricular remodeling and function are unclear. METHODS: Fifty-eight patients with a first anterior myocardial infarction and significant disease only in the left anterior descending coronary artery on arteriography performed after 7 to 10 days were evaluated. All patients received thrombolytic therapy. Residual stenosis of the infarct-related artery was measured with quantitative coronary arteriography. Left ventricular volumes and ejection fraction were measured by echocardiography and radionuclide angiography, respectively, 7 to 10 days, 6 months and 1 year after infarction. End-diastolic and end-systolic left ventricular volumes were measured by two-dimensional echocardiography and normalized to body surface area. Patients were classified into three groups according to baseline residual stenosis severity: total occlusion (Group I), minimal lesion diameter less than 1.5 mm (Group II) and minimal diameter greater than or equal to 1.5 mm (Group III). RESULTS: Group I patients had significantly greater left ventricular end-diastolic and end-systolic volumes at 6 months and 1 year than did the other groups. Group II patients had greater end-diastolic and end-systolic volumes than did Group III patients at 1 year. In addition, Group I patients had a lower ejection fraction at 1 year than that of the other groups. The minimal lesion diameter was significantly correlated with percent change in end-diastolic volume at 1 year. CONCLUSIONS: The severity of the baseline residual stenosis of the infarct-related artery is an important predictor of change in left ventricular volumes in the 1st year after infarction. Total occlusion of the infarct-related artery is associated with greater left ventricular dilation and functional impairment.

Cardiac Catheterization↗
PubMed1992

Ventricular rate-adaptive pacing in the elderly.

The role of ventricular rate-adaptive pacing (VVIR) in the elderly was investigated in 12 patients with a mean age of 85 +/- 2 years (range 75-95 years) with implanted activity-initiated VVIR pacemakers. Although four patients had significant extracardiac diseases, all were capable of independent walking and self care. The pacing rate achieved during structured daily activities (walking, climbing stairs, washing, bed-making and scrubbing floors) were compared with those achieved by 10 age-matched healthy subjects. Apart from the more strenuous activities (ascending stairs and floor-scrubbing), the pacing rates achieved by the patients were comparable to those of the healthy subjects and occurred within an appropriate time. In a 4-weekly randomized, double-blind crossover protocol in the VVI and VVIR pacing modes, all patients underwent assessments in a 12-min walking distance test, a 24 h non-invasive ambulatory blood pressure recording and a symptomatic documentation. During VVIR pacing, the 12-min walking distance was significantly improved compared to VVI pacing (556 +/- 52 vs. 545 +/- 55 m, P less than 0.05). There was no difference between the recorded blood pressure and symptom scores between the two pacing modes, although most patients preferred VVIR pacing (P less than 0.05). It is concluded that VVIR pacing in this elderly population can improve exercise capacity, and the patients' preference for the VVIR mode was documented despite the absence of a measurable difference in symptomatology.

Aged↗
PubMed1992

The use of implantable sensors for the control of pacemaker mediated tachycardias: a comparative evaluation between minute ventilation sensing and acceleration sensing dual chamber rate adaptive pacemakers.

The role of implantable sensors to control pacemaker mediated tachycardias was investigated in 16 patients with two different dual chamber rate adaptive (DDDR) pacemakers, which sensed eiter minute ventilation (DDDR-Meta, nine patients) or body acceleration (Relay, seven patients). Successive atrial sensed events beyond a programmable rate occurring in the absence of detection of exercise by the sensors were considered to represent retrograde conduction or atrial arrhythmias, and the pacemakers responded by either a mode shift from DDDR to ventricular rate adaptive (VVIR) pacing (DDDR-Meta) or by tracking at an interim rate, the so-called conditional ventricular tracking limit (CVTL, Relay). In the unipolar atrial sensing mode, myopotential sensing (MPI) and external chest wall stimulations (CWS) at 250 beats/min were induced to be preferentially sensed by the atrial channel to simulate the conditions of atrial arrhythmias. In the DDD mode, these maneuvers resulted in ventricular responses of 88 +/- 3 beats/min and 110 +/- 3 beats/min for MPI and CWS, respectively. The pacing rate was significantly reduced in the DDDR mode with the sensors correctly detecting and responding to the sensed abnormal atrial signals (68 +/- 5 beats/min during MPI and 71 +/- 5 beats/min during CWS, P less than 0.005 compared with the corresponding DDD rate). One patient with a Relay pacemaker developed spontaneous atrial flutter and the ventricular tracking responses were 140 and 85 beats/min in the DDD and DDDR pacing modes, respectively. Thus MPI and CWS are useful bedside testing methods to assess pacemaker response during atrial arrhythmias. The use of implantable sensors to judge the appropriateness of atrial rate is a new approach to the management of pacemaker mediated tachycardias.

Adult↗
PubMed1992

Atrial arrhythmia management with sensor controlled atrial refractory period and automatic mode switching in patients with minute ventilation sensing dual chamber rate adaptive pacemakers.

Although a long postventricular atrial refractory period (PVARP) may prevent the occurrence of pacemaker mediated tachycardias and inadvertent tracking of atrial arrhythmias in dual chamber (DDD) pacing, the maximum upper rate will necessarily be compromised. We tested the feasibility of using minute ventilation sensing in a dual chamber rate adaptive pacemaker (DDDR) to shorten the PVARP during exercise in 13 patients with bradycardias (resting PVARP = 463 +/- 29 msec) to avoid premature upper rate behavior. Graded treadmill exercise tests in the DDD and DDDR modes at this PVARP resulted in maximum ventricular rates of 98 +/- 8 and 142 +/- 3 beats/min, respectively (P < 0.0001), due to chronotropic incompetence and upper rate limitation in the DDD mode, both circumvened with the use of sensor. In order to stimulate atrial arrhythmias, chest wall stimulation was applied for 30 seconds at a rate of 250 beats/min at a mean unipolar atrial sensitivity of 0.82 mV. Irregular ventricular responses occurred in the DDD mode (the rates at a PVARP of 280 and 463 +/- 29 msec were, respectively 92 +/- 5 and 66 +/- 3 msec; P < 0.0001). In the DDDR mode at a PVARP of 463 +/- 29 msec, regular ventricular pacing at 53 +/- 2 beats/min occurred due to mode switching to VVIR mode in the presence of repetitive sensed atrial events within the PVARP. One patient developed spontaneous atrial fibrillation on follow-up, which was correctly identified by the pacemaker algorithm, resulting in mode switch from DDDR to regular VVIR pacing and preservation of rate response. In conclusion, sensor controlled PVARP allows a long PVARP to be used at rest without limiting the maximum rate during exercise. In addition, to offer protection against retrograde conduction, a long PVARP and mode switching also limit the rate during atrial arrhythmias and allow regular ventricular rate responses according to the physiological demands.

Aged↗
PubMed1992

Initial clinical experience with a single pass VDDR pacing system.

Although ventricular rate adaptive pacing (VVIR) improves exercise capacity and cardiac output compared to constant rate ventricular pacing (VVI), this pacing mode does not provide benefit of atrioventricular (AV) synchrony. We evaluated the use of a custom-built VDDR pacing system using a single pass, ventricular lead, which detects endocavity P wave using a pair of diagonally arranged atrial bipolar (DAB) electrodes. In the VDDR mode, AV synchrony is enabled and the P wave rate is used in conjunction with an accelerometer based activity sensor for rate adaptive pacing. A VDDR pacemaker was implanted in three patients with complete AV block (mean age 63 +/- 1 year) and the mean implantation time was 29 minutes. Mean P wave amplitude was 2.4 mV (1.2-4.2 mV) at implantation and telemetered P wave amplitude was stable over a follow-up of 6 months. At a sensitivity of 0.2 mV, stable P wave sensing was observed during breathing maneuvers, arm swinging, myopotential induction, and Holter recording. Paired exercise tests performed in the VDDR and VVIR modes showed higher cardiac output at rest, during exercise, and in the recovery period in the VDDR pacing mode. Thus VDDR pacing using a single pass lead is superior to VVIR pacing by enabling P synchronous ventricular pacing without adding to the complexity of implantation.

Acceleration↗
PubMed1992

The range of sensors and algorithms used in rate adaptive cardiac pacing.

Implantable sensors play an important role in physiological cardiac pacing. Sensors can be classified according to the technical methods in which sensing is achieved: the sensing of the evoked ventricular response, intrathoracic impedance and body acceleration forces, and the incorporation of special sensors on pacing electrodes. These sensors differ in their relative merits in terms of speed, proportionality, sensitivity, and specificity of rate response. The efficacy of a sensor can be significantly modified by the algorithm used in relating sensor signal to a pacing rate change. The currently available types of sensors and algorithms are summarized and compared in this review article. The relative merits of these sensors and algorithms form the basis for designing a multisensor pacing system.

Algorithms↗
PubMed1992

Clinical experience with an activity sensing DDDR pacemaker using an accelerometer sensor.

The rate adaptive characteristics and pacemaker mediated tachycardia protection algorithm of an accelerometer based DDDR pacemaker were evaluated in 11 patients with bradycardia (seven atrioventricular block, four sick sinus syndrome). Rate adaptive programming was effected by collecting the acceleration level during a 3-minute moderate exercise ("tailoring" of sensor). In comparison with an externally attached piezoelectric sensor, the accelerometer sensor showed lower rate changes during external tapping of the pacemaker (16 +/- 3 vs 29 +/- 4 ppm, P less than 0.02) and applied direct pressure (1 +/- 1 vs 40 +/- 3 beats/min, P less than 0.001) on the pacemaker. At nominal setting, the accelerometer sensor showed improved rate stability and higher rate response to jogging and standing, although responses to other daily activities and treadmill exercise were similar. Apart from changing the rate responsive slope, rate response could be improved by repeat "tailoring" of the sensor at a lower exercise level, resulting in better overall rate response characteristics. The ability of the rate monitoring software to collect acceleration levels for an activity and profile the projected rate response at different rate responsive settings allowed programming to be effected with the minimum amount of exercise testing. The pacemaker also discriminated atrial tachyarrhythmias from normal sinus response using the sensor to judge the appropriateness of the atrial rate, which correctly identified and prevented rapid ventricular tracking in two patients during atrial flutter/fibrillation.

Adult↗
PubMed1992

Bidirectional tachycardia induced by herbal aconite poisoning.

This report details the clinical, electrocardiographic, and electropharmacological characteristics of an unusual case of bidirectional tachycardia induced by aconites present in a Chinese herbal decoction consumed by a previously healthy subject. The tachycardia showed marked susceptibility to vagotonic maneuvers, cholinesterase inhibition, and adenosine triphosphate. The incessant nature of the tachycardia, rapid recurrence after transient suppression, and failure to respond to direct current cardioversion suggested an automatic tachycardia mechanism consistent with known data on the cellular electrophysiological mechanism of aconitine-mediated arrhythmogenesis. A fascicular or ventricular myocardial origin of the tachycardia with alternating activation patterns, or dual foci with alternate discharge, appeared most plausible. The rootstocks of aconitum plants have been commonly employed in traditional Chinese herbal recipes for "cardiotonic" actions and for relieving "rheumatism." Multiple pitfalls could occur during the processing of these herbs that might have predisposed to aconite poisoning. The need for strict control and surveillance of herbal substances with low margins of safety is highlighted.

Aconitum↗
PubMed1992

Age-related differences in basal and calcium-stimulated plasma calcitonin levels in female rats.

The effects of aging on calcitonin (CT) secretion in female rats were investigated. Old (24 mo) at constant diestrus status and young (2 mo) at diestrus status rats were either ovariectomized (Ovx) or left intact as controls. Ovx rats were injected subcutaneously with estradiol benzoate (25 micrograms/kg body wt) or sesame oil one time per day for 3 days. All rats were infused with CaCl2 (10 mg/ml) at a rate of 2 ml/h for 30 min via a jugular catheter connected to a peristaltic pump. Blood samples (0.5 ml each) were collected at 0, 30, 60, and 120 min. The basal and post-CaCl2 levels of plasma Ca measured with radioimmunoassay were significantly higher (P less than 0.05-0.01) in old than in young female rats. The pre- and post-CaCl2 levels of plasma Ca and CT in young rats were not altered by Ovx or estradiol replacement. In old rats, Ovx caused a higher (P less than 0.01) level in plasma CT at 0 and 30 min after CaCl2 infusion. Both basal and stimulated levels of plasma CT were higher (P less than 0.01) in old Ovx than in young Ovx rats. These results demonstrated that 1) the increase of plasma CT in response to Ca challenge was greater in old than in young female rats, 2) the influence of estradiol and ovarian function on plasma CT concentration increases as a function of age, and 3) estradiol reduced the plasma CT in response to hypercalcemia in old Ovx rats. The sensitivity of the target tissue of young rats may be lower in response to the modulation of estrogen during hypercalcemia without compromising the secretion and hypocalcemic effect of CT in young rats. All suggested an age-related relationship between estrogen and CT secretion in minute-to-minute regulation during Ca infusion in rats.

Aging↗
PubMed1992

Hypocalcemia and myocardial function in uremia.

To investigate whether hypocalcemia affects cardiac performance in uremic patients, we studied the hemodynamic changes with short- and long-term correction of hypocalcemia in 4 uremic patients on dialysis using continuous wave Doppler study. At rest, 1 h of intravenous calcium infusion increased calcium level from 1.74 +/- 0.17 to 1.92 +/- 0.16 mmol/l (p less than 0.05). Cardiac output represented by minute distance increased from 10.5 +/- 2.0 to 12.1 +/- 2.5 m (p less than 0.05), but heart rate and blood pressure were unchanged. The peak velocity and acceleration of ascending aortic blood flow increased during calcium infusion. With long-term replacement, calcium level increased from 1.74 +/- 0.17 to 1.94 +/- 0.15 mmol/l (p less than 0.05), but resting hemodynamics were unchanged. On exercise testing, exercise duration increased from 10.6 +/- 1.6 min to 12.9 +/- 1.5 min (p less than 0.01), but hemodynamic parameters at peak exercise were similar. We conclude that acute calcium replacement enhanced cardiac contractility in uremic patients, but cardiac performance at rest and peak exercise was not improved with long-term therapy. This reflects different cardiac responses to acute versus chronic calcium replacement.

Adult↗
PubMed1992

Incessant automatic ventricular tachycardia complicating acute coxsackie B myocarditis.

A 13-year-old girl presented with incessant ventricular tachycardia complicating acute Coxsackie B3 myocarditis. Electrophysiologic assessment revealed that the tachycardia could not be terminated, overdrive suppressed or accelerated by programmed electrical stimulation, but was transiently slowed by intravenous adenosine triphosphate and had marked spontaneous and sympathoautonomic-mediated fluctuation in the tachycardia cycle length. These features were atypical of reentry and triggered automaticity and suggested that abnormal automaticity was the likely tachycardia mechanism. Intravenous amiodarone slowed the ventricular tachycardia, but the patient eventually succumbed from rapidly progressive left ventricular failure. Postmortem pathohistologic examination confirmed the diagnosis of acute myocarditis.

Adolescent↗