The utility of the electrocardiogram in detecting heart disease in resource poor settings

2017-06-01T05:01:51Z (GMT) by Lee, Geraldine Anne
Cardiovascular disease remains a leading cause of death and a considerable disease burden, especially in low to middle income countries. With increasing urbanization and epidemiologic transition, there is a significant increase in the prevalence of life-style related risk factors which contribute to the global burden of cardiovascular disease and in particular heart disease. With growing evidence highlighting the catastrophic physical and financial effects of heart disease and its associated risk factors, there is a need to detect heart disease via preventive or screening programs in a cost effective manner. There are several diagnostic tests available, among these the 12-lead electrocardiogram (ECG). Previous studies have examined the ECG in epidemiological studies in high income countries and reported moderate sensitivity and high specificity. However, there is a paucity of studies from low to middle income countries and in resource poor locations. The aim of this thesis was to systematically examine the 12-lead ECG in two diverse resource poor communities- Soweto in South Africa (from the Heart of Soweto study) and Alice Springs (from the Heart of the Heart study) in the Northern Territories, Australia. ECG analysis was undertaken in those deemed free of heart disease and in those with common forms of heart disease using the Minnesota code and the Sokolow Lyon voltage criteria (to measure left ventricular hypertrophy). As well as obtaining a 12-lead ECG, comprehensive clinical assessments were performed including anthropometric measurements, blood pressure measurements, heart and lung sounds, recording of any clinical symptoms such as angina, breathlessness, oedema, dizziness and palpitations. Echocardiography was obtained on the majority of participants and this allowed analysis with electrocardiographic data to be made. Where applicable, blood tests and other diagnostic tests were performed as well as documentation of previous medical history. The results in this thesis present data from two locations where there has previously been a paucity of contemporary data available. This study evaluated more than 2,700 ECGs for the purpose of describing ECG characteristics and data in those with established disease and confirmed heart disease-free participants. Using echocardiography to confirm individuals free of heart disease in Sowetans, a total of 387 ECGs were analysed. Of these, 27% demonstrated major ECG abnormalities (defined as Q waves, ST segment changes and conduction abnormalities) and 42% demonstrated minor ECG abnormalities (namely tall R waves, inverted T waves and ST elevation). These findings suggest in this population, further delineation is required between these normal physiological variants (that is minor abnormalities) and abnormal characteristics associated with underlying cardiac pathologies. Specifically examining those with heart failure (n=756), major ECGs abnormalities were evident in 91% of ECGs and 97% of ECGs demonstrated minor abnormalities. Further analyses across a broad spectrum of conditions including heart failure and cardiomyopathies (n=1927) revealed a high proportion of ECGs with major ECG abnormalities (54%) including LVH (as measured by Sokolow Lyon > 38mm), bundle branch blocks and major Q waves and ST/T wave changes. All of these ECG characteristics have previously been identified as important prognostic markers in those with diagnosed heart disease. Although no distinctive ECG characteristics were associated with specific conditions, but rather an increased prevalence of major abnormalities across the spectrum from coronary artery disease to dilated cardiomyopathy with valve disease was observed. A corresponding decline in cardiac dysfunction was also evident in echocardiographic parameters. Analysis of ECGs from Australian Aboriginals (n=340) validated the commonly applied Caucasian parameters in this cohort with no deviation from the currently used parameters. In those with heart disease (n=70), rheumatic heart disease and valve disease were common and major ECG abnormalities evident in nearly half of these ECGs. To determine if the ECG was a valid method of detecting underlying heart disease, sensitivity and specificity was calculated using the echocardiogram as the gold standard. Calculating the sensitivity in the African cohort revealed a sensitivity of 88% and specificity of 48% while the Heart of the Heart study revealed a sensitivity of 54% and specificity of 71%. Based on these findings the 12-lead ECG has a limited ability to detect underlying heart disease with a high rate of false negatives. Clinically, these data demonstrate the complexity of disease in this cohort and suggests that the presence of major ECG abnormalities strongly supports underlying heart disease and should be further investigated by echocardiography but given the high number of ECG abnormalities in those deemed heart disease free, the 12-lead ECG has a limited ability to detect underlying heart disease in these resource poor settings.