Ischaemic heart disease in a young man.
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Biomedical subjects
Publications and source records attributed to Y T Tai.
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Although exercise testing has been advocated to unmask proarrhythmic potentials in patients receiving flecainide acetate, the effects of this drug on exercise parameters in individuals without structural heart disease have not been reported. This study was undertaken to assess the effects of flecainide on hemodynamics and electrocardiographic changes during exercise testing in 24 patients with paroxysmal supraventricular tachyarrhythmias, who had normal cardiac structure and sinus node function. Paired treadmill exercise tests using the Bruce protocol were performed after 1 week of treatment with flecainide (200 mg/day) or placebo in a double-blind, randomized design. Exercise testing was terminated because of either fatigue or dyspnea in all subjects. Although resting heart rate was unaffected, flecainide reduced the exercise heart rate (expressed as a percentage of age-predicted maximum) compared with placebo (84 +/- 12% vs. 92 +/- 9%, p < 0.001). Neither resting and exercise systolic blood pressure nor exercise duration were affected. PR interval shortening with exercise was not affected by flecainide, whereas QRS was prolonged compared with placebo (20 +/- 9% vs. 0 +/- 8%, p < 0.01). Compared with placebo, flecainide significantly shortened QTc (-7 +/- 12% vs. 0 +/- 8%, p < 0.05) and JTc (-34 +/- 11% vs. -21 +/- 11%, p < 0.01) intervals during exercise. During exercise, flecainide produced significant depression in the sinus node automaticity and manifested use-dependent slowing of ventricular conduction and acceleration in ventricular repolarization.
When activated by a point mutation in its transmembrane domain neu is an extremely potent transforming oncogene when expressed in rodent mammary parenchyma. This extreme potency led Muller et al. (13) to suggest the possibility that neu might transform mammary cells by a single step. A corollary to a single-step transformation hypothesis is that transformation efficiency cannot be modulated. Here we test this corollary by introducing mutated neu into in situ rat mammary cells using retroviral vectors and following infection by hormonally modulating recipient rats. Hormonal modulation included raising prolactin levels and lowering glucocorticoid levels. This modulation promotes radiation, chemical and ras initiated mammary carcinogenesis. Here we report that this hormonal promotion protocol also increased the yield of mammary carcinomas following the introduction of the mutated neu gene. We conclude that mutated neu is not a single-step transformer but is a very potent event in the multistage process of mammary carcinogenesis.
This study aims to evaluate the impact of transcatheter radiofrequency ablation on quality-of-life (QOL) and exercise capacity in patients with paroxysmal supraventricular tachycardia (SVT) on stable medical therapy and the extent of symptomatic benefits of this treatment in patients with SVT of different clinical severity. A total of 55 patients with SVT on stable medications for 3 months were randomly selected for either radiofrequency ablation treatment (46 patients) or continuation of medical therapy (medical control group, 9 patients). Severity of SVT was classified based on the frequency and duration of SVT episodes, hemodynamic disturbance, and the presence of preexcited atrial fibrillation during an episode. Treadmill exercise capacity (Bruce protocol) and QOL (questionnaire study and interview) were assessed before and at 3-month intervals for 1 year after the radiofrequency procedure and at 3 months in the medical control group. Thirty-six of 46 patients were successfully ablated in one session, and a QOL measure before and at 3 months after ablation in these patients showed an improvement in total scores for "General Health Questionnaire" (20.3 +/- 6.2 vs 16.9 +/- 5.3, P < 0.01), "Somatic Symptoms Inventory" (73.0 +/- 6.0 vs 76.1 +/- 4.1, P < 0.02), and "Sickness Impact Profile" (12.6 +/- 1.7 vs 4.9 +/- 3.9, P < 0.01). This improvement in QOL was progressive and sustained over a 1-year period. Major arrhythmia limitations, such as apprehension of strenuous activities and long distance travel, were alleviated after a successful procedure. The extent of improvement in QOL was significant for patients considered to have "mild" or "severe" arrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)
Mixed venous oxygen saturation (SvO2) is a physiologic parameter reflecting cardiac output (CO) and tissue oxygen utilization. An implantable oxygen sensor incorporated in a right ventricular pacing lead has been developed to assess the feasibility of ambulatory monitoring of SvO2 to predict cardiorespiratory parameters. Eight patients with a mean age of 62 +/- 2 years and sinoatrial disease received an SvO2-driven dual-chamber rate-adaptive pacemaker capable of continuous SvO2 measurement. During graded maximal exercise with measurement of oxygen consumption (Vo2), arterial oxygen saturation (SaO2), and telemetered derived SvO2 data, CO was assessed using the Fick principle. The accuracy of the derived CO was compared with CO measured directly by continuous-wave Doppler assessment of the ascending aortic flow. The maximum changes in SvO2 and SaO2 during exercise were 25 +/- 5 and 3 +/- 1%, respectively. SvO2 was significantly correlated with Vo2 (r = 0.9 +/- 0.1, p < 0.001), work done (r = 0.8 +/- 0.1, p < 0.05), and minute ventilation (r = 0.9 +/- 0.1, p < 0.05). Doppler-derived CO was significantly correlated with CO estimated from SvO2 measured (r = 0.8 +/- 0.1, p < 0.05) and is expressed as 46x derived CO +300. Although continuous SvO2 sensing was originally developed to increase pacing rate during exercise, its use can be extended for monitoring cardiopulmonary performance on an ambulatory basis. This may be useful as a direct assessment of cardiopulmonary status in diseased states and also as an objective means to evaluate cardiac response to medical therapy in patients with heart failure.
Two Hong Kong Chinese adults were prescribed aconitine-containing herbal preparations by Chinese herbal practitioners for relief of minor musculoskeletal pain. After ingestion both quickly developed ventricular tachycardia followed by ventricular fibrillation and cardiac arrest refractory to resuscitation; death in both cases occurred within 12 h of ingestion. Neither had a history of cardiac disease. Coroners' autopsies showed no significant macroscopic or microscopic findings, with no evidence of ischaemic heart disease or other cardiac disease. Toxicological examination of stomach contents showed a trace of hydrolysed aconitine in one case but was negative in the other. Analysis of the herbal preparations consumed, however, confirmed the presence of the aconitine-containing herbs in quantities greatly in excess of the maximum recommended in the P.R. China pharmacopoeia. Both patients therefore consumed an accidental overdose of aconitine, which has a narrow safety margin between therapeutic analgesic effect and its known cardiotoxic effect. These particular herbal medicines are controlled substances in mainland China and Taiwan, but no controls on their dispensing exist in Hong Kong. Together with reported non-fatal cases of aconitine poisoning, these cases emphasise that legal controls of the dispensing and use of aconitine-containing herbal preparations are necessary in Hong Kong.
Adenosine is an efficacious diagnostic and therapeutic agent in the acute management of wide complex tachycardias. Its potent negative dromotropic effect terminates supraventricular tachycardias involving the atrioventricular node, allowing differentiation from tachycardias of atrial and ventricular origin. Its extranodal actions, however, may lead to potential pitfalls in arrhythmia diagnosis. We report three unusual cases of patients with adenosine-sensitive tachycardias. One patient had idiopathic ventricular tachycardia originating from the right ventricular outflow tract, one had ectopic atrial tachycardia, and one had atrial fibrillation with rate-related intraventricular aberration. Recognition of the extranodal actions of adenosine and careful ECG evaluation before and after adenosine administration should maximize the diagnostic accuracy of adenosine in wide complex tachycardias.
An atrial-based pacing mode is superior to ventricular constant rate demand pacing (VVI) mode in patients with sick sinus syndrome (SSS) by providing both rate adaptation and atrioventricular (AV) synchrony. The use of a non-atrial sensor to overcome chronotropic incompetence and preserve normal intrinsic AV conduction in pacemaker therapy for SSS was investigated in 15 consecutive patients (mean age 66 +/- 2 years). All had intact AV conduction (antegrade conduction capacity > 100 beats.min-1 and an atrial paced to intrinsic R interval of < or = 220 ms). DDDR pacemakers capable of being programmed into atrial rate adaptive (AAIR), dual chamber rate adaptive (DDDR) and ventricular rate adaptive (VVIR) modes were used. Beginning with an acute study, arterial pressure was invasively assessed in each pacing mode during physiological stresses and low level exercise. In the ambulatory phase, the incidence of ventricular pacing and arrhythmias (Holter recording), diurnal blood pressure changes (ambulatory blood pressure recording), and symptom and quality of life level (questionnaires and interviews) were compared. Despite similar heart rate changes during acute physiological stresses, a higher blood pressure was recorded during AAIR or DDDR pacing compared with VVIR pacing. Systolic blood pressure over 24 h was lower in the VVIR mode (122 +/- 5 mmHg) than AAIR/DDDR pacing (129 +/- 6/128 +/- 6 mmHg, P < 0.05). VVIR pacing was associated with a higher frequency of atrial and ventricular ectopics, with two patients developing paroxysmal atrial fibrillation. Ventricular pacing was used in a higher percentage in the DDDR compared with the VVIR mode (64 +/- 11 and 39 +/- 7%, P < 0.03). VVIR pacing was associated with more palpitations, a lower level of general well being and depression. Despite the use of a sensor to overcome chronotropic incompetence, VVIR pacing is a less satisfactory pacing mode for SSS. Although AAIR/DDDR pacing may achieve similar haemodynamic and clinical status, in patients with intact AV conduction, AAIR pacing may be preferable by avoiding an abnormal ventricular activation pattern.
Established electrophysiological criteria indicating anatomical proximity to an accessory pathway include early ventricular or atrial activation during antegrade or retrograde accessory pathway conduction, recording of accessory pathway potentials, and pace map concordance. This article describes two cases of RF catheter ablation of accessory pathways, during which positioning of the mapping catheter at specific sites on the endocardial aspect of the atrioventricular annulus led to prolongation of accessory pathway refractoriness and/or slowing of conduction. RF energy application at these sites successfully abolished accessory pathway conduction. When observed on an "internal" basis during catheter mapping, catheter induced stunning of accessory pathway conduction provides evidence of satisfactory electrode-tissue contact in addition to anatomical proximity, and may give additional predictive value to successful transcatheter accessory pathway ablation.
Rapid ventricular tracking response to supraventricular tachyarrhythmia is one major limitation to DDD pacing. In a DDDR pacemaker, sensor-based algorithms have been used to control these arrhythmias. These include the use of an interim rate limit (conditional ventricular tracking limit) or a separate maximum tracking and sensor rate limits (discrepant upper rate). These algorithms limit inappropriate ventricular pacing rate during tracking of pathological supraventricular tachyarrhythmia and atrial flutter by Wenckebach-like prolongation of the AV interval. We observed that this may cause an unexpected extension of the AV interval in patients with high atrial rate and intact AV nodal conduction. This was due to P wave rate above the conditional ventricular tracking limit or maximum tracking limit, but AV paced interval prolongation was avoided by the occurrence of intrinsic conduction, albeit at an AV interval longer than the programmed AV interval. This might appear as failure of ventricular pacing on the ECG. This phenomenon is a modified form of "upper rate" behavior occurring in the AV interval, and should be recognized as a normal behavior rather than pacemaker malfunction.
Central venous oxygen saturation (SvO2) closely reflects cardiac output and tissue oxygen consumption. In the absence of an adequate chronotropic response during exercise, SvO2 will decrease and the extent of desaturation may be used as a parameter for rate adaptive cardiac pacing. Eight patients with sinoatrial disease received a DDDR pacemaker capable of DDDR pacing by sensing either SvO2 or piezoelectric detected body movement. Both sensors were programmed to attain a rate of about 100 beats/min during walking, and with the lower and upper rates set at 50% and 90% of age predicted maximum, respectively. Chronotropic behavior of the two sensors were compared in the DDD mode with measurement of sensor responses, during everyday activities (walking, stair climbing, postural changes, and physiological stresses) and at each quartile of workload during a continuous treadmill exercise test. During walking at 2.5 mph, both sensors showed no significant difference in delay time (both react within 15 secs) or half-time (SvO2 = 36 +/- 12 sec and activity 24 +/- 3 sec; P = NS), although SvO2 driven pacing achieved 90% target rate response slower than activity sensing (124 +/- 16 sec vs 77 +/- 10 sec; P < 0.02). SvO2 pacing was associated with a more physiological rate response during walking upslope (68 +/- 12 beats/min vs 57 +/- 10 beats/min; P < 0.05), ascending stairs (59 +/- 10 beats/min vs 31 +/- 6 beats/min; P < 0.05), and standing (34 +/- 7 beats/min vs 9 +/- 2 beats/min; P < 0.05). The SvO2 sensor significantly overpaced in the first quartile of exercise (51.8 +/- 25.6% in excess of heart rate expected from workload), but the rate was within 20% of expected for the remainder of exercise. "Underpacing" was observed with the activity sensor at the higher workload. In conclusion, the SvO2 sensor demonstrated a more physiological response to activities of daily living compared with the activity sensor. Using a quantitative method, the speed of onset of rate response of the SvO2 sensor was comparable to activity sensing, and was more proportional in rate response. Significant overpacing occurs at the beginning of exercise during SvO2 driven pacing, which may be improved with the use of a curvilinear algorithm.
Although differences in exercise performance have been observed between different rate adaptive modes, the relative impact of atrioventricular (AV) synchrony and rate adaptation on quality of life (QOL) have not been determined. Thirty-three patients with either sinoatrial disease (18) or complete atrioventricular (AV) block (15) received DDDR pacemakers (16 minute ventilation sensing, 17 activity sensing). There were 11 males and 22 females, with a mean age of 66 +/- 1 (range 39-78) years. The study was a double-blind, triple cross-over study comparing DDDR, DDD, and VVIR modes. At the end of each 8-week study period in each mode, QOL was assessed by a questionnaire evaluating patients' functional class (Classes I-IV), physical malaise inventory (41 items), illness perception (43 items), and overall QOL rating based on a 48 items measure covering different aspects of the patients' daily life adjustment. Two patients required early crossover from VVIR mode during the study. Patients experienced significantly fewer physical malaise such as temperature intolerance, dyspnea, and palpitations in the DDDR mode, compared with either DDD or VVIR pacing. DDDR pacing reduced the perception of illness in 5 of 43 items compared to VVIR pacing, and improved stamina and appetite compared to DDD pacing. The overall QOL score was 102 +/- 2, 105 +/- 2, 113 +/- 2 in the DDDR, DDD, and VVIR modes, respectively, with a higher score indicating a poorer QOL (DDDR/DDD vs VVIR, P < 0.02). There was no change in functional classes between the three pacing modes.(ABSTRACT TRUNCATED AT 250 WORDS)
Optimal function of a single lead P wave synchronous rate adaptive ventricular pacing system (VDDR) requires reliable P wave sensing over time and during daily activities. The stability of P wave sensing and the incidence of sensitivity reprogramming in a single pass lead with a diagonally arranged bipole was assessed in 30 patients with complete atrioventricular block over a follow-up period of 12 +/- 1 months (range 6 months to 3 years). Atrial sensing was assessed during clinic visits, by physical maneuvers (postural changes, breathing, Valsalva maneuver, walking and isometric exercise), maximum treadmill exercise and Holter recordings. P wave amplitude at implantation was 1.21 +/- 0.09 (0.5-3.6) mV, and the atrial sensing threshold remained stable over the entire period of follow-up. Using an atrial sensitivity based on twice the sensing threshold at 1 month, P wave undersensing was found in 2, 4, 3, and 7 patients during clinic visit, physical maneuvers, exercise, and Holter recordings, respectively. Atrial sensitivity reprogramming was performed in three patients based on the correction of undersensing during physical maneuvers. Although eight patients had atrial undersensing on Holter recordings, the number of undersensed P waves was small (total 101 beats or 0.013% +/- 0.001% of total ventricular beats) and no patient was symptomatic. One patient had intermittent atrial undersensing at the highest sensitivity, but the VDDR mode was still functional most of the time. No patient had myopotential interference at the programmed sensitivity. One patient developed chronic atrial fibrillation and was programmed to the VVIR mode. Thus, single lead VDDR pacing is a stable pacing mode in 97% of patients.(ABSTRACT TRUNCATED AT 250 WORDS)
Endocardial P wave amplitude (PWA) is an important determinant of the atrial sensing capabilities of an atrial-based pacing system. Although changes in PWA during physical activities are known to occur in DDD/R pacing, there is little information on the P wave stability in single pass lead VDD/R pacemakers using floating P wave sensing. We investigated the variation of PWA during daily life activities using telemetry recorded atrial electrograms in 21 patients with DDDR pacemakers (Relay or Elite) and 29 patients with single lead VDD/R pacemakers (Unity or Thera). Physical activities resulted in marked individual variability of PWA but, as a group, there was no significant difference between PWA during sitting, standing, lying down, and coughing in both DDDR and VDD/R pacing. In the Elite II pacemaker, walking at 2 miles per hour resulted in significant reduction of PWA (11.6% compared with sitting, P < 0.05). The most consistent reduction in PWA occurred in the relaxation phase of the Valsalva maneuver (VM), with all pacemakers showing a reduction in PWA (mean reduction in PWA compared with sitting in DDDR and VDD/R were 16.6% and 12.8%, respectively). Two patients with DDDR pacemakers (Relay) and three patients with VDD/R pacemakers (1 Unity and 2 Thera) had atrial sensing failure during VM or walking. In conclusion, large variation in PWA occurs during daily life activities. The extent of variation is dependent on the patients, types of atrial lead, and the maneuvers performed. A twice sensing threshold may be insufficient to ensure adequate atrial sensing during these activities.(ABSTRACT TRUNCATED AT 250 WORDS)
Although multisensor pacing may mitigate the inadequacy of rate adaptation in a single sensor system, the clinical role of multisensor driven rate adaptive pacing remains unclear. The cardiopulmonary performance of six patients (mean age 63.5 +/- 10 years) who had undergone the implant of combined QT and activity VVIR (Topaz) pacemakers was assessed during submaximal and maximal treadmill exercise with the rate response sensor randomly programmed to either single sensor mode, QT and activity (ACT), or dual sensor mode, with equal contribution of QT and ACT (QT = ACT). The rate of response, the proportionality, oxygen kinetics, and maximal exercise performance of the various sensor modes during exercise were measured and compared. The ACT sensor mode "overpaced" and the QT and QT = ACT sensor modes "underpaced" during the first three quartiles of exercise (P < 0.05). The ACT sensor mode also gave the fastest rate of response with the shortest delay (13 +/- 1.5 sec vs 145 +/- 58 sec and 41 +/- 17 sec, P < 0.05), time to 50% rate response (39 +/- 2.7 sec vs 275 +/- 48 sec and 203 +/- 40 sec, P < 0.05), and time to 90% of rate response (107 +/- 21 sec vs 375 +/- 34 sec and 347 +/- 34 sec, P < 0.05) and a smaller oxygen debt (0.87 +/- 0.16 L vs 1.10 +/- 0.2 L and 1.07 +/- 0.18 L, P < 0.05) compared to the QT and QT = ACT sensor modes, respectively. These differences were most significant at low exercise workloads. Thus, different sensor combinations result in different rate response profiles and oxygen delivery, especially during low level exercise.(ABSTRACT TRUNCATED AT 250 WORDS)
The use of multiple His bundle-right bundle branch recordings in electrophysiologic studies has facilitated definition of the mechanism and elucidation of the direction of impulse propagation in bundle branch reentrant tachycardia, "Mahaim" fiber reciprocating tachycardia, and retrograde His depolarization in fascicular or ventricular tachycardias. This report details the electrophysiologic evaluation of pleomorphic ventricular tachycardia in a patient with advanced coronary heart disease. The ventricular tachycardia at baseline revealed variation in the QRS duration without alteration of the electrocardiographic (ECG) morphology. Following flecainide administration, a ventricular tachycardia with close resemblance of the ECG morphology to sinus rhythm was induced. Proximal and distal His-bundle recordings revealed early antegrade His-bundle activation during this tachycardia. Programmed stimulation converted this tachycardia back to the clinical ventricular tachycardia with intermittent narrowing of the QRS complexes. Early His activation was evident only during the narrower complexes but not in the tachycardia beats with wide complex. Penetration of the His bundle by ventricular tachycardia, with resultant fusion from intramyocardial ventricular activation and His-Purkinje activation, could have accounted for the near normalization of the QRS morphology during the ventricular tachycardia.
STUDY OBJECTIVE: The aim was to describe the distribution of lipids and apolipoproteins in the Chinese population in Hong Kong. DESIGN: This was a prospective, cross sectional, population based survey. SETTINGS: The study was conducted in a single, self referred, out patient screening centre. PARTICIPANTS: Altogether 825 Chinese adults aged > or = 20 years were screened. One hundred subjects who had previously had lipid measurement and 29 who were taking lipid modifying drugs were excluded but 289 men and 407 women remained for further analysis. MAIN RESULTS: Age standardised mean (SEM) lipids concentrations for Hong Kong Chinese were total cholesterol: men, 5.48 (0.05) mmol/l and women, 5.46 (0.06) mmol/l; triglycerides: men, 1.22 (1.03) mmol/l and women, 1.00 (1.03) mmol/l; high density lipoprotein (HDL) cholesterol: men, 1.25 (0.02) mmol/l and women, 1.42 (0.02) mmol/l; low density lipoprotein (LDL) cholesterol: men, 3.56 (0.05) mmol/l and women, 3.50 (0.06) mmol/l; apolipoprotein A-I (apo A-I): men, 1.34 (0.01) g/l and women, 1.46 (0.01) g/l; and apolipoprotein B (apo B): men, 1.15 (0.02) g/l and women, 1.06 (0.02) g/l. The total to HDL cholesterol ratios were men, 4.62 (0.07) and women, 4.10 (0.08); and apo B to apo A-I ratios (apo B/A) were men, 0.88 (0.02) and women, 0.75 (0.02). While levels of total cholesterol, LDL cholesterol, apo B, triglycerides, total/HDL cholesterol, and apo B/A were positively associated with age in both sexes and were higher in men before the age 50-59 years, they rose steeply thereafter in women to cross over the levels in men. In contrast, HDL cholesterol decreased with age while apo A-I remained constant, and both were consistently higher in women than in men in all age groups. CONCLUSIONS: Hong Kong Chinese have attained lipid profiles similar to those in other developed western populations. Environmental factors seem influential in this regard. Faced with the increasing coronary mortality of recent years, there should be a major effort to reduce the cholesterol concentrations in this population.
In 3 fatal cases of tachyarrhythmia caused by herbal poisoning, the only common denominator was the presence of aconites derived from the rootstocks and lateral root-tubers of Aconitum carmichaeli and the rootstocks of A kusnexoffii. The contain aconitine alkaloids which are notorious for the arrhythmogenic properties. Symptoms of these cases and management suggestions are presented.