published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Community Medicine / Master / Master of Public Health

Cardiac arrest is a phenomenon in which a sudden loss of heart function leads to cessation of blood delivery to the rest of the body. It is one of the leading causes of natural death in the United States. Because its onset cannot be predicted, therapy for post-cardiac arrest victims focuses on management of moderate organ failure and neurological injury. The mortality rate of out-of-hospital cardiac arrest victims remains about 90%, but currently, there are several management techniques that reduce the incidence of sudden cardiac death. My goal is to argue that despite some of the negative effects of therapeutic hypothermia, it holds the most promise to sustain organ and neurological recovery. This study focuses on evaluating the pathophysiology of post-cardiac arrest syndrome, and referencing literature that documents the reversal techniques of therapeutic hypothermia. Despite the side effects and unwanted consequences that come with targeted temperature management, there is an imbalance between the benefits and consequences, resulting in enhanced recovery when this technique is carefully administered shortly after the cardiac arrest episode.

Thesis (M.P.H.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 13).

Thesis (M. Med. Sc.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 34-49)

Survivors of out-of-hospital cardiac arrest (OHCA) are at risk for hypoxic-ischemic brain injury, which can cause a broad range of effects from death to subtle cognitive impairment. This dissertation includes two studies of OHCA patients who had made good neurological recovery after OHCA. In both studies, patients were evaluated near the time of hospital discharge, when crucial decisions such as rehabilitation plans are made. In addition, OHCA survivors were compared with a myocardial infarction (MI) control group in both studies. Study 1 explored the frequency, severity, and predictors of cognitive dysfunction in OHCA survivors, and characterized the cognitive profile of these patients using a comprehensive neuropsychological battery. Study 2 explored grey matter volume (GMV) in OHCA survivors, MI patients, and healthy controls, and correlated these with cognitive dysfunction and important clinical characteristics (e.g., downtime). While OHCA patients performed poorer on cognitive testing than MI patients, both groups showed decreased GMVs compared to healthy controls. OHCA survivors who have had good neurological recovery may still face significant challenges when they re-engage in difficult cognitive tasks post-arrest. To date, these cognitive issues after OHCA have been somewhat overlooked in Canada's healthcare system. A better understanding of hypoxic-ischemic brain injury among survivors will aid in the promotion of targeted interventions and rehabilitation efforts, and may help clinicians predict those who are most at risk.

Death due to lethal cardiac arrhythmias is the leading cause of mortality in Western society. Many of the fundamental mechanisms underlying the onset of arrthythmias, their maintenance and termination, still remain poorly understood. The specialized conduction (or His-Purkinje) system is fundamental to ventricular electrophysiological function and is a key player in various cardiac diseases. In recent years, computational simulation has become an important tool in im- proving our understanding ofthese mechanisms. Current state-of-the-art computational ventric- ular electrophysiology models often do not feature a detailed representation of the specialized conduction system. Ventricular models that do incorporate the specialized conduction system often use a simplified anatomical description and are commonly based on the monodomain equations, rather than the more general bidomain equations. Thus, using computational simula- tion to investigate both normal physiological function of the specialized conduction system and pathologies in which it is involved presents difficulties. This thesis develops the techniques and tools required to model the specialized conduction sys- tem at the ventricular scale. We derive one-dimensional bidomain equations that model elec- trical propagation in the system by reducing the equations associated with a three-dimensional fibre. To complement the derived equations, we develop a numerical solution scheme for the model that is efficient enough to allow ventricular simulations. The one-dimensional bido- main model allows defibrillation studies to be performed with the specialized conduction sys- tem. Secondly, we investigate the imaging and mesh generation tools required to integrate an anatomically detailed mesh of the specialized conduction system into a current state-of-the-art ventricular mesh. Using these tools, a highly detailed rabbit-specific specialized conduction system anatomical model is developed. Simulations are performed that dem~strate the re- sponse of the specialized conduction system to defibrillation strength shocks and we compare activation sequences generated using the model to experimental recordings. Finally, we investi- gate variability in the anatomy of the system. The tools and ventricular model presented in this thesis fulfil an important role in allowing the study of the e1ectrophysiological function of the specialized conduction system at the ventricular scale.

Background According to data from Department of Health, in 2011 heart diseases was the second commonest leading cause of death in Hong Kong [13]. Shortening the time from cardiac arrest to Cardio-pulmonary Resuscitation (CPR) could increase the chance of survival. If the brain of the patient who suffers from cardiac arrest does not receive oxygen within 4 minutes, severe brain damage might occur [14]. In some countries like US and Finland, dispatcher will give CPR instruction to caller when cardiac arrest is recognized. Therefore, the patient could receive early CPR before the arrival of paramedics. If dispatcher-assisted CPR is implemented in Hong Kong, the chance of survival of out-of-hospital cardiac arrest (OHCA) patient could be increased. Objective 1. To evaluate whether it is evident that dispatcher-assisted CPR and dispatcher instruction [22] would improve survival of OHCA. 2. To evaluate whether these measures could be implemented in Hong Kong. Data Source PubMed was searched for articles in English language with no limit set for time of the study. The keywords were dispatcher-assisted CPR and out of hospital. No inclusion criteria were set on the publication type and other details. Results Initial PubMed search resulted in 24 articles. After reviewing the abstracts, 10 articles were selected for full-text assessment. Finally, four relevant articles were selected for the literature review. Of the four papers, two were retrospective cohort studies; one was before-after comparison study while the remaining one was randomized control trial. Three papers (Rea et al, Eisenberg et al, and Kuisma et al.) used the survival to hospital discharge as the effect measure for the primary outcome to evaluate the effectiveness of dispatcher-assisted CPR. The remaining paper (Hallstrom et al.) mainly studied the potential benefit and harm from dispatcher-assisted CPR. Using no bystander CPR as the reference group, the multivariate adjusted odds ratio of survival was 1.45 (95% CI, 1.21, 1.73) for dispatcher-assisted bystander CPR and 1.69 (95% CI, 1.42, 2.01) for bystander CPR without dispatcher assistance [2]. The percentage of total bystander-initiated CPR increased from 45% to 56% after the programme (difference: 11.1%, 95% CI, ±9.3%). Besides, the percentage discharged for dispatcher-assisted CPR group after the programme was 15% higher than that before the programme [6]. The most important findings are related to the number of cardiac arrest calls in that when the dispatcher handled on less than 4 Ventricular Fibrillation (VF) calls during the study period, the survival to hospital discharge was 22.1% compared to 38.2% and 39.4% when the dispatcher handled 4 to 9 calls or more than 9 calls (p = 0.0227 for the three groups) [8]. With telephone guided CPR, the survival to hospital discharge was 43.1% compared with 31.7% when CPR instructions were not provided (p = 0.0453) [8]. In patients (n = 3,320) receiving advanced cardiac life support (ACLS) a total of 993 (29.9%) was found to be benefited from dispatcher-assisted CPR [7]. Conclusion Instructions by dispatcher can improve bystander CPR rates, which in turn increases the chance of survival [26]. Dispatcher-assisted CPR is worth considering to be recommended to all callers reporting a patient in cardiac arrest in Hong Kong. / published_or_final_version / Public Health / Master / Master of Public Health

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains vi, 79 p. Includes abstract. Includes bibliographical references.

Background-Emergency 9-1-1 callers use a wide range of terms to describe abnormal breathing in persons with out-of-hospital cardiac arrest (OHCA). These breathing descriptors can obstruct the telephone cardiopulmonary resuscitation (CPR) process. Methods and Results-We conducted an observational study of emergency call audio recordings linked to confirmed OHCAs in a statewide Utstein-style database. Breathing descriptors fell into 1 of 8 groups (eg, gasping, snoring). We divided the study population into groups with and without descriptors for abnormal breathing to investigate the impact of these descriptors on patient outcomes and telephone CPR process. Callers used descriptors in 459 of 2411 cases (19.0%) between October 1, 2010, and December 31, 2014. Survival outcome was better when the caller used a breathing descriptor (19.6% versus 8.8%, P<0.0001), with an odds ratio of 1.63 (95% confidence interval, 1.17-2.25). After exclusions, 379 of 459 cases were eligible for process analysis. When callers described abnormal breathing, the rates of telecommunicator OHCA recognition, CPR instruction, and telephone CPR were lower than when callers did not use a breathing descriptor (79.7% versus 93.0%, P<0.0001; 65.4% versus 72.5%, P=0.0078; and 60.2% versus 66.9%, P=0.0123, respectively). The time interval between call receipt and OHCA recognition was longer when the caller used a breathing descriptor (118.5 versus 73.5 seconds, P<0.0001). Conclusions-Descriptors of abnormal breathing are associated with improved outcomes but also with delays in the identification of OHCA. Familiarizing telecommunicators with these descriptors may improve the telephone CPR process including OHCA recognition for patients with increased probability of survival.