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SCREENING FOR ELECTROCARDIOGRAPHIC ABNORMALITIES AMONG PATIENTS WITH TYPE 2 DIABETES MELLITUS SEEN AT THE JOS UNIVERSITY TEACHING HOSPITAL, JOS, PLATEAU STATE, NIGERIA
Abstract
Background:
Type 2 diabetes mellitus has become epidemic world wide since the past decades owing to the advancing age of the population, a substantially increased prevalence of obesity, and decreased physical activity, all of which have been attributed to a western lifestyle. Cardiovascular morbidity is a major burden in patients with type 2 diabetes mellitus, and electro cardio-graphic changes are commonly observed in patients with diabetes.
In Nigeria, no recent studies have been carried out despite the ever-increasing prevalence of type 2 diabetes mellitus.
Objective:
To describe the pattern of electrocardiographic abnormalities in type 2 diabetes seen in Jos University Teaching Hospital (JUTH).
The first 250 consecutive diabetic patients aged 30-85 years, who presented at the general outpatient and diabetic clinics were recruited for the study after giving their informed consent.
Patients with vascular heart disease or known structural cardiac disease ( like ventricular septal defects or aortic stenosis, congestive heart disease and chronic respiratory disease like tuberculosis and asthma were excluded from the study, because their conditions could produce ECG changes not due to
diabetics.
The electrocardiograms were subjected to the Minnesota coding and the patients were asked questions based on WHO multinational questionnaire adapted for an African population.
The data was analysed using the computer software of Epi info 2003. Two tailed X2 tests were used to identify associations between covariates and ECG abnormalities. The independent effect of each potential risk factor for electrocardiographic changes were tested.
Results:
A total of 100 (40%) subjects had ECG abnormalities. Only 4 (1.6%) had major ECG abnormalities; 3(1.2%) were coded coronary probable (definite myocardial infarction), while 1(0.4%) was coded coronary possible (likely myocardial infarction). Ninety six (38.4%), had minor ECG abnormalities. By clinical classification, 22 (8.8%) had angina pectoris, which was suggestive of myocardial ischaemia.
Possible predictors for electrocardiographic changes in a multivariate model were fasting blood glucose (p=0.1), cholesterol level (p=0.09), hypertension (0.01) and duration of diabetes (p=0.07).
Hypertension was significantly associated with electro cardio graphic changes in type 2 diabetes, (p=0.01), and therefore predictive of ECG changes in type 2 diabetes.
Conclusion:
It was evident from the results obtained, that ECG abnormalities are found in type 2 Nigerian diabetics, but they are still relatively low compared with results from the Western world.
The finding of a rising prevalence of myocardial infarction with associated ECG changes makes it necessary for all diabetics to be screened for abnormalities on first contact, so that the abnormalities can be diagnosed early for appropriate intervention.
TABLEOFCONTENTS
Title page … … … … … … … i
Declaration … … … … … … … ii Certification … … … … … … … iii
Dedication … … … … … … … iv
Acknowledgement … … … … … … … … … … v
Table of contents … … … … … … … … … … vi
List of Tables and figures … … … … … … … … … vii
List of abbreviations … … … … … … … … … … viii
Abstract … … … … … … … … … … … xi
CHAPTER ONE
Introduction
1.1 Definition … … … … … … … … … … 1
1.2 Statement of research problem … … … … … … … 6
1.3 Aim and objectives of the study … … … … … … … 7
1.4 Justification of the study … … … … … … … … 8
CHAPTER TWO …………………………………………………………….
2.2 Pathophysiology of cardiovascular disease in diabetes……………………………………………………… 13
2.3 Electrocardiographic changes in diabetes mellitus……………………………………………………………. 15
2.4 Risk factors for cardiovascular disease and electrocardiographic changes in diabetes…………… 28
Literature Review
2.1 Epidemiology of type 2 DM … … … … … … … … 11
2.4.1 Atherogenic dyslipidaemia … … … … … … … 28
2.4.2 Metabolic syndrome … … … … … … … … 29
2.4.3 Hyper – homocysteinaemia … … … … …. 30
2.4.4 Cigarette smoking … … … … 31
2.5 Prevention of cardiovascular disease in type 2 diabetes 31
2.5.1 Diet … … … … … … … 34
2.5.2 Exercise … … … … … … 35
2.5.3 Antioxidant therapy … … … … … 37
2.6 Management of diabetes mellitus … … … … … … … 37
2.6.1 Non – pharmacological management … … … … … … … 38
2.6.2 Pharmacological management … … … … … … … 38
CHAPTER THREE
Materials and method
3.1 Setting … … … … … … … … … … … 48
3.2 Study population … … … … … … … … … 49
3.3 Consent for the study … … … … … … … … … 49
3.4 Sample size … … … … … … … … … … 49
3.5 Inclusive/exclusion criteria … … … … … … … … 50
3.6 Sampling technique … … … … … … … … … 50
3.6 Sampling technique … … … … … … … … … 50
3.7 Data collection … … … … … … … … … 53
3.8 Statistical analysis … … … … … … … … … 54
3.9 Scores for diagnosis … … … … … … … … … 55
CHAPTER FOUR
Results
4.1 Socio – demographic characteristics of patients … … … … 55
4.1.1 Sex distribution … … … … … … … … 55
4.1.2 Age distribution … … … … … … 55
4.1.3 Occupation … … … … … 58
4.2 Other associated illnesses … … … … 58
4.3 Smoking … … … … … … 58
4.4 Distribution of subjects according to body mass index 60
4.5 Cardiovascular status of respondents … … … 61
4.6 Distribution of electrocardiographic abnormalities … … … … … 61
4.6.1 Age distribution of patients according to ECG abnormalities … … … 61
4.6.2 Distribution of patients by sex according to ECG abnormalities … … … 62
4.6.3 Relationship of ECG abnormalities with occupation … … … … … 62
4.6.4 Relationship of body mass index with ECG abnormalities … … … … 62
4.6.5 Relationship of ECG abnormalities with fasting blood glucose level … … 63
4.6.6 Relationship of ECG abnormalities with systolic blood … … … … 63
4.6.7 Relationship of ECG abnormalities with diastolic blood pressure … … … 63
4.6.8 Relationship of ECG abnormalities with pulse rate … … … … … 63
4.6.9 Relationship of ECG abnormalities with duration of diabetes … … … 64
4.6.10 Relationship of ECG abnormalities with lipids levels … … … … 66
4.7 Relationship of ECG abnormalities with self reported abnormalities … … 66
4.8 Association between the characteristics of subjects and ECG abnormalities … … 69
CHAPTER FIVE
5.1 Discussion … … … … … … … … … … 72
5.2 Electrocardiographic abnormalities and age … … … … … … 72
5.3 Electrocardiographic abnormalities with sex … … … … … … 73
5.4 Electrocardiographic abnormalities and occupation … … … … … 74
5.5 Electrocardiographic abnormalities with body mass index … … … 74
5.6 Electrocardiographic abnormalities with fasting blood glucose level … 76
5.7 Electrocardiographic abnormalities with hypertension … 77
5.8 Electrocardiographic abnormalities with pulse rate 77
5.9 Electrocardiographic abnormalities with smoking status 78
5.10 Electrocardiographic abnormalities and duration of diabetes 79
5.11 Triglyceride level with ECG abnormalities … … 80
5.12 Electrocardiographic abnormalities and self reported abnormalities 81
5.13 Strengths … … … … … … … … … … 81
5.14 Weaknesses/limitations … … … … … … … … 84
5.15 Conclusion and implication of this study for family medicine … … … 85
5.16 The unanswered question … … … … … … … … 85
5.17 Need for further study … … … … … … … … … 86
References … … … … … … … … … …
Appendix : (1) approved form
- informed consent statement
- questionnaire for ECG abnormalities
CHAPTER 1
INTRODUCTION
1.1 Definition
Diabetes mellitus (DM) is a syndrome complex characterized by chronic hyperglycaemia due to disturbances of carbohydrate, fat and protein metabolism associated with absolute or relative deficiencies in insulin action and/or insulin secretion.1,2
Diabetes mellitus has been described as a chronic often debilitating disease with severe complications including blindness, heart and kidney disease and neuropathy.2,3 Type 2 diabetes is the commonest type of diabetes mellitus in adults in developing countries 2,4 It is a non-ketotic form of diabetes mellitus, and unlike type 1 diabetes it is not linked to HLA markers on the sixth chromosome or associated with islet cell auto antibodies 5. Type 2 diabetes has a more marked genetic component than Type 1 diabetes. The concordance rate between identical twins has been estimated at 6090%5.Having one first degree relative with type 2 diabetes doubles the risk of developing the disease, and having two relatives with the disease quadruples the risk6 Further evidence for a genetic basis is the marked differences in prevalence among racial and ethnic groups. In the USA, type 2 diabetes is almost twice as common in blacks as it is in whites. In Mexican-Americans, the relative prevalence is two and a half to three times as common as in whites. In native Americans it is five times as common7. Clearly, type 2 diabetes is a heterogeneous disorder that can be caused by many genetic
abnormalities8.
Type 2 diabetes forms part of the metabolic syndrome and therefore has close association with
hypertension and ischaemic heart disease2,6. Diabetes mellitus interferes with important metabolic processes in the body resulting in dysfunction of affected organs. Therefore, disturbed metabolism of carbohydrate, fat and protein in diabetes may cause atherosclerosis and coronary artery disease9.
Diabetic heart disease is multifactorial and multifaceted,9 The modes of presentation include coronary artery disease, autonomic cardiac denervation, specific heart muscle disease, (Diabetic cardiomyopathy), and subclinical left ventricular dysfunction with associated risk factors like obesity, hypertension and hyperlipidaemia9.
Type 2 diabetes mellitus is associated with a two to three fold increased risk of cardiovascular morbidity and mortality10. The risk is approximately two fold in men and four fold in women11. The risk of coronary artery disease is increased four fold in diabetic persons compared with non-diabetic persons, and the risks of myocardial infarction and death from coronary artery disease are the same in diabetic persons without previous myocardial infarction as in non-diabetics with previous myocardial infarction11,12 The relative risk for stroke in diabetic persons is two to three fold the risk in non-diabetic persons, and there is greater relative risk in women compared with men10,12. The vascular diseases associated with diabetes mellitus are varied. They can be non-specific (atherosclerosis and arteriosclerosis) or specific (microangiopathy or endothelial proliferative changes of the arterioles).
The former, primarily involves large vessels especially in the legs, heart and brain of older patients. The latter is localized to small vessels and may be seen in patients of all ages10.
Coronary artery disease is the leading cause of death among adult diabetics and accounts for about three times the risk of death among diabetics as among non-diabetics. The incidence of coronary artery disease correlates more closely with the duration of diabetes than with its severity. Coronary artery disease is a common, serious and an insidious complication of diabetes. It occurs early and has many atypical features, including silent (painless) ischaemia.5
The frequency of acute myocardial infarction is not only increased in diabetic patients, but also the treatment of the infarct is more complicated than in non-diabetic patients. Patients with acute myocardial infarction, regardless of the control of their diabetes before hospital admission, exhibit significantly higher mortality and morbidity than do non-diabetics 12.
Peripheral somatic neuropathy is a commonly recognized complication of diabetes mellitus. Autonomic neuropathy also occurs in diabetics leading to diarrhoea, vomiting and other gastrointestinal disturbances. A form of autonomic dysfunction involving the heart is autonomic cardiac denervation (cardiac autonomic dysfunction)10. It is an important and a common companion of diabetic peripheral neuropathy5.
In two large series, cardiac autonomic neuropathy was present in more than a third of the patients and accompanied by depression of left ventricular function9.
The severity of cardiac dysfunction is directly related to the severity of autonomic neuropathy12 Occasionally it may be present before clinical symptoms of generalized autonomic neuropathy are demonstrable. Furthermore, the neuropathy may involve the sympathetic nervous system and/or the parasympathetic nervous system. Indeed, it may become so severe as to lead to total cardiac denervation. These changes in adrenergic nervous system function result in a fixed, rapid heart rate that barely responds to physiological stimuli, such as the Valsalva manoeuver, carotid sinus pressure, or tilting,5 or drugs like phenyl-ephrine, atropine, or propanolol. These denervated hearts rarely develop arrythmias. Diabetics with abnormal autonomic function tests have markedly decreased survival with an increased risk of sudden death.
Diabetes mellitus appears to increase the likelihood of the development of congestive heart failure from all causes, possibly due to diabetes induced cardiomyopathy. The risk of developing heart failure in diabetics was found to be increased four to five folds.12 This increased risk remained high even when patients with prior coronary or rheumatic heart disease were excluded.
This increased risk persisted after age, blood pressure, weight, and cholesterol values, as well as coronary heart disease, were taken into account.12 On the basis of these findings, it appeared that the excessive risk of heart failure in diabetic patients is caused by factors other than accelerated atherogenesis and coronary heart disease.
Diabetic cardiomyopathy (specific heart muscle disease) may occur in individuals who have no evidence of large vessel disease or abnormality in myocardial capillary basal lamina documented by endo-myocardial biopsies 10,12. The most common histologic abnormalities are interstitial fibrosis and arteriolar hyalinization. Both systolic and diastolic dysfunction may be present even in children with diabetes mellitus10. The severity of dysfunction is related to the degree of metabolic control even in the absence of clinical evidence of cardiovascular or micro-vascular disease10.
Abnormality of ventricular function (subclinical left ventricular dysfunction) are detectable by echocardiography. This shows a reduction in the peak diastolic filling,9,10 abnormal left ventricular ejection fraction in response to exercise and evidence of diastolic dysfunction, even in normotensive diabetic patients9. However, diastolic dysfunction worsens with the duration of diabetes.9
The electrocardiogram is a standard tool in the diagnosis of cardiac abnormalities notwithstanding its limitations, and remains a crucial tool in the identification and management of acute myocardial infarction. It is a simple, painless test and an essential adjunct to the clinical history and physical examination13. The electrocardiograph represents a recording of the amplified currents generated during contractions of the various muscle units of the heart. Diseased hearts due to diabetes or other conditions like hypertension or electrolyte imbalance produce records, which differ significantly from the normal13. The electrical events of each heartbeat are represented by important waves as the P, QRS, and T waves. The P represents both atrial contractions, QRS represents the ventricular contraction while T-wave represents the recovery phase of the ventricle before the next cycle12,13.
It is a cost-effective approach for the diagnosis of electrocardiographic changes, which occur in type 2 diabetes, especially, when all the parameters of ECG, are considered. For a comprehensive electrical study of the heart the electrocardiographic records are taken from various standardized directions. Twelve Leads are usual. Leads, I, II III; VR, Vl, Vf, (limb leads, and six uni-polar chest Leads – V1 – V6. Leads I, II and VL record the cardiac events mostly on the left lateral aspect, Leads II and Vf from the inferior part of the heart, while lead VR record from the upper right angle [ i.e. the atria] , leads V1 and V2 record
from the right ventricle, leads V3 and V4 – the septum and leads V5 and V6 record events from the left ventricle.
The resting ECG tests are used commonly14. Electrocardiographic changes in diabetes includes ST segment depression with or without T – wave inversion, supra-ventricular tachycardia, first degree atrio-ventricular block, atrial fibrillation, left bundle branch block, right bundle branch block, Wolfe Parkinson White syndrome, left axis deviation, voltage abnormalities, pathologic Q waves, and qs waves.
1 .2 STATEMENT OF RESEARCH PROBLEM
Diabetes mellitus occurs worldwide, affects almost all populations, both sexes, adults and young people alike. It is emerging as a growing problem in developing countries, 4 with the commonest type among adults being the type 2 diabetes mellitus3.
In Nigeria, diabetes mellitus is presently the most common endocrine metabolic disorder encountered.3 The prevalence of diabetes mellitus has been estimated to range from 1.0% to 6% and 2.4% – 4.1% in Nigeria4. The prevalence of diabetes mellitus in Jos is 3.1% (males 4.1% and female 2.4%) age adjusted to Jos population.15 The prevalence of ECG abnormalities (ST segment depression, T-wave inversion, supraventricular tachycardia left bundle branch block, right bundle branch block, left axis deviation, and myocardial infarction) in diabetic Nigerians conducted forty years ago was 0.6% and this was not comparable to 11% obtained in Belgium seven years ago.17
Since this last study in Nigeria, no other study of ECG abnormalities in diabetes has been reported despite the increasing prevalence of diabetes in Nigeria and in Jos.
Over the years, evidence of overt and subclinical disease of the heart associated with diabetes mellitus has accumulated, and they include coronary artery disease, hypertension, congestive heart failure and myocardial infarction.9 Type 2 diabetes mellitus is associated with a two to five fold increased risk of cardiovascular morbidity and mortality. The risk of coronary heart disease is increased four fold in diabetic persons compared with non-diabetic persons but the risk of myocardial infarction (MI) are the same as in non-diabetic persons.12 Although static and cardiovascular function indices and systolic function indices did not differ between non-diabetics and diabetics, measures of diastolic function were significantly worse in diabetics than controls. This was found to worsen with the duration of diabetes and related to the existence of microangiopathy.10 The implication is that type 2 diabetics in Nigeria may have diastolic dysfunction and/or other serious but subclinical cardiac abnormalities like silent myocardial infarction.
A study of diabetic cardiomyopathy in JUTH,9 using echocardiographic techniques, showed a significantly higher resting heart rate . This increase was considered a reflex response to maintain cardiac output suggesting a decreased cardiac reserve in diabetic patients.9
1.3 AIM AND OBJECTIVES OF THE STUDY.
To describe the pattern of ECG abnormalities in type 2 Nigerian diabetics seen in Jos University Teaching Hospital in order to raise awareness among physicians on the need for ECG screening of diabetics.
Objectives
- To determine the nature of the ECG abnormalities in type 2 diabetics seen in JUTH.
- To determine the proportion of type 2 diabetics with evidence of ischaemic
heart disease
- To determine which factors are associated with ischaemic heart disease in patients with type 2 diabetes.
1.4 JUSTIFICATION OF THE STUDY.
Type 2 diabetes mellitus has become epidemic in the past several decades owing to the advancing age of the population, a substantially increased prevalence of obesity, and decreased physical activity, all of which have been attributed to a western lifestyle18.
In the USA, almost 8 percent of the adult population and 19 percent of the adult population older than age 65 years have diabetes.18 About 800,000 new cases of diabetes mellitus are diagnosed yearly, almost all of which are type 2. Apart from the known risk factors for diabetes, several racial and ethnic groups in the USA are at particularly high risk for diabetes and its cardiovascular complications, including Blacks, Hispanics, Asians, Pacific Islanders and native Americans. Seventy two percent of type 2 diabetics die of cardiovascular disease.19,20 More so the development of cardiovascular disease appears to preceed the development of diabetes mellitus itself in association with sub-diabetic levels of hyperglycaemia.19,20
In the USA, the estimated cost of providing care for diabetes and its complications is $ 100 billion per year, with half of the cost attributable to direct care18.
In Nigeria, the current prevalence of ECG abnormalities among type 2 diabetics is not known and therefore the estimated cost of providing care for diabetes and its complications is not known.
Given the high frequency of asymptomatic cardiovascular disease among diabetics in western countries, it is important to determine if cardiovascular disease is equally prevalent among Nigerian diabetics.
Studies of ECG abnormalities carried out among Kenyan diabetics showed a prevalence of 15.6%.21 Investigators17 in Belgium found that ischaemic- like changes on the ECG were comparable between men and women (9.0% and 9.8% ), but the prevalence of minor abnormalities was slightly higher among men (10.4% and 9.5% ) than women17
Members of the London cohort of the WHO multinational study of cardiovascular disease in diabetics were followed up for mortality for 12years. During this period, 92 of the 497 patients died. The commonest cause of death was cardiovascular diseases accounting for 55.4% of all deaths.9
Many diabetic patients present first to family physicians and are more likely to receive continued, comprehensive care from family physicians. Therefore, the family physician needs to understand the pathophysiology of diabetes mellitus and its complications, diagnose them early using the ECG and provide possible preventive measures or delay worsening of the complications.
Claudi and co- workers22, after a large population screening of type 2 diabetics suggest that prevention of cardiovascular disease in diabetics requires earlier diagnosis of the diabetes.
Since ECG is cost effective it can be used in rural areas by family physicians unlike the echocardiogram, which is expensive and can only be used in special centers. Ischaemic heart disease is rare in Nigerian diabetics probably due to non/under reporting in contrast to rates reported in developed (western) countries while type 2 diabetes is common.
Because of the association of type 2 diabetes mellitus with substantial cardiovascular morbidity and mortality it must be recognized early and treated.
Preventive efforts along with early diagnosis of cardiovascular abnormalities in type 2 diabetics will delay onset of micro-vascular disease in persons with normal ECG and progression or further deterioration in patients with ischaemic heart disease
The result of this study is expected to enhance the family physician’s awareness of the prevalence of ECG changes in type 2 diabetics and the need for early diagnosis through screening. It is also expected to rekindle the interest of the family physician in understanding basic ECG for screening and appropriate interventions when necessary.
SCREENING FOR ELECTROCARDIOGRAPHIC ABNORMALITIES AMONG PATIENTS WITH TYPE 2 DIABETES MELLITUS SEEN AT THE JOS UNIVERSITY TEACHING HOSPITAL, JOS, PLATEAU STATE, NIGERIA
