University of Macau / Institute of Chinese Medical Sciences

Thesis (M.D.)--University of Hong Kong, 1989.

published_or_final_version / Medicine / Master / Doctor of Medicine

No description available.

Thesis (M.D.)--University of Hong Kong, 1989. / Also available in print.

Thesis (Ph. D.)--Ohio State University, 2005. / Available online via OhioLINK's ETD Center; full text release delayed at author's request until 2006 September 15.

No description available.

No description available.

Cardiac pacing has been the only effective treatment in the management of patients with symptomatic bradycardia caused by sinus node dysfunction or atrioventricular block for decades. Conventional dual-chamber pacing is performed by implanting two leads in right atrial (RA) appendage and right ventricular (RV) apex separately. RV apex is the most commonly applied pacing site because it can be easily reached and allows a chronically stable position and stimulation thresholds. However, large randomized clinical trials have suggested that right ventricular apical (RVA) pacing may cause abnormal ventricular contraction and reduce pump function and lead to myocardial hypertrophy, in particular in patients with impaired left ventricular (LV) function. Recent studies have also reported a reduced LV systolic function in patients with pacing indications and preserved ejection fraction. The deleterious effects of RVA pacing on LV function may be related to the abnormal electrical and mechanical activation pattern or ventricular dyssynchrony. During RVA pacing, conduction of the electrical wave front propagates slowly through ventricular myocardium rather than through the His-Purkinje conduction system, comparable to left bundle branch block (LBBB). In addition , RVA pacing alters ventricular synchrony and loading conditions which may result in diastolic heart failure with abnormal LV relaxation, high filling pressure and low cardiac output state. Furthermore, it is possible that left atrial (LA) remodeling and reduction of atrial function may occur during RVA pacing . However, it is not been carefully studied. / Echocardiography is a convenient, non-invasive and established tool to assess cardiac function in clinical practice. Conventional two-dimensional echocardiography is useful to assess cardiac chamber size, volume and function. With the development of real time three-dimensional echocardiography (RT3DE) and color tissue Doppler imaging (TDI), echocardiography provides further valuable information and more accurate measurements which include myocardial velocity and parameters of dyssynchrony. In the present study, the main echocardiographic parameters including the maximal left atrial volume (LAVmax), pre-atrial contraction volume (LAVpre) and the minimal left atria l volume (LAVmin) were assessed by two-dimensional echocardiography. Peak systolic (Sm-la), peak early diastolic (Em-la), peak late diastolic (Am-la) velocities of left atrium (LA) and atrial conduction time (from onset of P wave on electrocardiogram to onset of atrial velocity) were measured by TDI. / In a cross-sectional study, ninety-eight patients who had been implanted with RVA-based dual-chamber pacemakers were enrolled. Four patients with pacing dependent were excluded. Eventually 94 patients were included in the final analysis. Echocardiography was performed (iE33, Philips) during intrinsic ventricular conduction (V-sense) and RVA pacing (V-pace) modes with 15 minutes between switching modes. We aimed to investigate if RVA pacing has any acute effects on atrial remodeling and function in patients with preserved ejection fraction (LV ejection fraction> 45%). The result showed that during V-pace, LA volumes increased significantly when compared with V-sense (LAVmax: 52.0 +/- 18.8 vs. 55.2 +/- 21.1 ml, p = 0.005; LAVpre: 39.8 +/- 16.4 vs. 41.3 +/- 16.6 ml, p = 0.014; LAVmin: 27.4 +/- 14.0 vs. 29.1 +/- 15.1 ml, p = 0.001) . TDI parameters showed significant reduction in Sm-la (3.0 +/- 1.1 vs. 2.7 +/- 0.9 cm/s, p < 0.01), Em-la (2.7 +/- 1.1 vs. 2.4 +/- 1.0 cm/s, p = 0.001). However, there was no change in Am-la. / In a prospective study, patients with symptomatic bradycardia, preserved ejection fraction, and received RVA pacing were recruited. Echocardiography was performed at both baseline and one year follow up through a standard protocol by experienced echocardiographers. LA volumes and velocities as well as intra- and interatrial dyssynchrony were measured offline with the use of dedicated software. The objectives of this study were to investigate: (1) if RVA pacing has any deleterious effects on LA remodeling and function during long-term follow up; (2) if RA appendage pacing has separate effects on atrial pump function, intra- and interatrial dyssynchrony; (3) if atrial dysfunction and dyssynchrony can predict atrial high rate episodes (AHREs) burden in the first year of RVA pacing. The main findings of this study were: (a) at one year follow up, LA volumes and indexes were increased with reduction in passive emptying fraction and total emptying fraction. Atrial velocities showed significant reduction when compared with baseline; (b) in multivariate regression analysis, the ratio of transmitral early diastolic filling velocity to mitral annular early diastolic velocity (E/e') > 15 at one year and reduction of LV ejection fraction ≥ 5% were independent predictors of reduction of Am-la > 30%; (c) high percent of RA appendage pacing prolonged atrial conduction and induced intra- and interatrial dyssynchrony. (d) Am-la < 5.3 cm/s can predict AHREs burden which had a sensitivity of 71% and specificity of 75%. / In conclusion, our studies suggest even short-term RVA pacing induces LA dilatation and impaired passive atrial function, though it did not have direct effect on active atrial contractility. However, chronic RVA pacing results in LA remodeling and reduces atrial function with decreased contractility. This was more likely to occur in those with impaired LV ejection fraction and evidence of diastolic dysfunction. Atrial dysfunction and interatrial dyssynchrony can predict AHREs burden after chronic RVA pacing. Therefore, measures that may minimize such adverse effect of pacing on atrial function need to considered for patients receiving RVA pacing, such as the use of new pacing modalities. / Xie, Junmin. / "December 2010"--Abstract. / Adviser: Yu Cheuk Man. / Source: Dissertation Abstracts International, Volume: 73-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 142-161). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Reviews of clinical practice for paediatric pacemaker implantation and follow-up are necessary to provide an evidence-base for future policy and practice in this field. Epicardial pacing data available through Green Lane Hospital, New Zealand's (NZ) primary referral centre for paediatric cardiac surgery and pacemaker implantation, was reviewed with the following aims: Assessment of pacemaker lead performance over time in relation to the type of epicardial lead implanted - steroid-eluting (SE) and non steroid-eluting (NSE). Determination of the survival rate of epicardial leads. Identifying factors predicting or associated with lead failure.A database of pacing and sensing thresholds and lead impedance data at implant, 2, 6 and 18 weeks and 6 monthly intervals thereafter, was compiled and the prevalence and timing of complications in relation to lead type, location and implant route determined. In total 192 leads (155 SE, 37 NSE) were implanted in 96 patients (52 male) aged 3 days to 71 years (y) (median 1.7y), 74 patients were < 17 years of age at implant. Congenital heart defects were present in 82% of patients. Follow-up (f/u) was possible for 180 leads. Mean f/u duration for the 150 SE leads was 3.1y (2 weeks - 8.8y) and for the 30 NSE leads was 4.5y (2 weeks - 27y).SE and NSE pacing thresholds were similar at implant. NSE pacing thresholds peaked at 6 weeks post implant and remained significantly higher than SE leads throughout f/u in surviving leads, although the difference was small at 2 and 4 y. SE and NSE leads had similar ventricular sensing thresholds and lead impedances throughout the study period.Survival at 5 years for all leads was 61% (66% for SE leads and 41% for NSE leads). Primary causes of failure in the leads receiving f/u were exit block and lead fracture. The occurrence of exit block was significantly higher (p<0.0001) in NSE leads (57%) compared to SE leads (5%). Lead fracture occurred in 15% of leads with the highest fracture rate at 2-3 y post implant. Patient age and weight at implant, gender, previous cardiac surgery, lead polarity, indication for pacing and implant route were not predictors of lead failure. NSE leads were 6 times more likely to fail compared to SE leads (p <0.0001).The main study findings were: SE leads maintain lower pacing thresholds and a reduced incidence of exit block compared to NSE leads. It is therefore recommended that SE leads be developed which can penetrate fibrosed, scarred or fatty epicardial surfaces. Where SE lead use is contraindicated, alternative surgical techniques for SE lead placement should be attempted rather than implanting NSE leads. Lead fracture is a significant complication of epicardial pacing in paediatric patients. Using stronger bipolar leads implanted by the subxiphoid route may reduce the risk of fracture. Medium term survival (5 y) of SE epicardial leads is acceptable and therefore the continued use of these leads is recommended, particularly in young patients, allowing their veins to be saved for transvenous leads later in their life.