PROFILE OF ANKLE BRACHIAL INDEX AMONG ADULT PATIENTS ATTENDING GENERAL OUT-PATIENTS’ CLINIC OF OLABISI ONABANJO UNIVERSITY TEACHING HOSPITAL SAGAMU

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PROFILE OF ANKLE BRACHIAL INDEX AMONG ADULT PATIENTS ATTENDING GENERAL OUT-PATIENTS’ CLINIC OF OLABISI ONABANJO UNIVERSITY TEACHING HOSPITAL SAGAMU

SUMMARY

The ankle brachial index (ABI) is a ratio of Doppler recorded systolic blood pressure in the arteries supplying the legs and central aortic pressure (approximated by measuring the blood pressure in the arm). It is used to assess patients for peripheral arterial disease (PAD) as a fall in blood pressure in an artery at the ankle relative to the central blood pressure would suggest a stenosis in the arterial conduits somewhere in between the aorta and the ankle. This condition is usually asymptomatic and associated with increased risk of cardiovascular morbidity and mortality.

As a result of the relatively easy access to peripheral circulation, ABI can readily be measured to identify asymptomatic individuals thus allowing institution of preventive measures against serious brain and heart clinical atherosclerotic disease. However, despite this clinical usefulness of ABI, it is often not considered for use during cardiovascular assessment of patients.

The risk factors for low ABI are the same as the traditional risk factors for cardiovascular diseases (advancing age, hypertension and diabetes among others.) and patients with these risk factors are daily encountered in the general out-patients’ clinic (GOPC) of Olabisi Onabanjo University Teaching hospital (OOUTH). It is desirable to incorporate the measurement of their ABI with the aim of determining the pattern of ABI and the prevalence of PAD. The specific objectives were to establish their baseline ABI, determine the prevalence of PAD and the risk factors for low ABI among the sampled population.

To achieve these, a cross sectional study of 400 subjects selected by systematic random sampling and aged 50 years and above was carried out at the GOPC of OOUTH, Sagamu. In the method used, their socio-demographic data, cardiovascular risk factors (hypertension, diabetes, cigarette smoking, body mass index and blood cholesterol level) and ABI were assessed and collated with the aid of a questionnaire. The ABI values of 0.91-1.3, ≤ 0.9 and >1.3 were taken as normal, low and high ABI respectively.

The results were as follows: The age range of the participants was 50 – 86 years with a mean of 62.5 ± 9.29 years. There were one hundred and forty four (36.0%) males and two hundred and fifty six (64.0%) females giving a male to female ratio of 1:1.8.

Two hundred and eighty eight (72.0%) of the participants had normal ABI, ninety nine (24.8%) had low ABI and thirteen (3.3%) had high ABI. From these, the prevalence of PAD was 24.8% with ninety seven (24.3%) having mild PAD and two (0.5%) having moderate PAD.

The mean age of the participants for low ABI was 70.32 while the mean age for high and normal ABI was 72.00 and 62.51 respectively. Also the prevalence of low ABI increased sharply from 4.9% between 50-59 years to 25.3% and 58.7% between 60-69 and ≥70

respectively without significant gender differences.

The largely asymptomatic nature of PAD was shown by the finding of intermittent claudication among only 6.3% of the entire participants and in just 17.2% of those with low ABI. Of the cardiovascular risk factors assessed, the prevalence of diabetes mellitus and hypertension was higher and had statistically significant relationship with low ABI.

In conclusion, the prevalence of PAD as diagnosed by ABI was 24.8%. The age of the participants was a significant risk factor for low ABI as shown by the sharp rise in prevalence after the 5th decade of life. Additional significant risk factors for low ABI were diabetes mellitus and hypertension. Also of note was the low prevalence of intermittent claudication among the participants with low ABI highlighting its limited use in the screening for PAD. The clinical implication of these findings is that beyond the 5th decade of life and among patients with diabetes mellitus and hypertension, screening for PAD using ABI should be included as part of their clinical evaluation and primary prevention strategy. Reliance on the presence of intermittent claudication even among those at risk of PAD will result in underestimating the true burden of PAD.

TABLE OF CONTENTS

Title                                                                                                                              Pages

Title page and author                                                                                                         1

Declaration                                                                                                                         11

Certification                                                                                                                       111

Acknowledgement                                                                                                             1V

Dedication                                                                                                                          V

Table of contents                                                                                                                V1

List of Tables                                                                                                                     1X

List of Figures                                                                                                                    X

List of Abbreviations                                                                                                         X1

SUMMARY                                                                                                                      1

CHAPTER ONE

1.0. Introduction                                                                                                         4

1.1. General objective                                                                                                6

1.2. Specific objectives                                                                                              6

CHAPTER TWO

2.00. Literature Review                                                                                              7

2.01. Risk Factors for peripheral Arterial Disease                                                     9

2.02. Diagnosis of Peripheral Arterial Disease                                                          15

2.03. Intermittent Claudication                                                                                   16

2.04. Physical Examination                                                                                        17

2.05. Ancillary Investigations                                                                                     19

2.06. Angiography                                                                                                      19

2.07. Definition Ankle Brachial Index                                                                       20

2.08. Historical Perspective and Epidemiology                                                         21

2.09. Methods of Measuring Ankle Brachial Index                                                   22

2.10. Interpretation of Ankle Brachial Index                                                             24

2.11. Ankle Brachial Index as a Biomarker of Cardiovascular Risk                         24

2.12. Sensitivity and Specificity of Ankle brachial Index                                          25

2.13. Ankle Brachial Index and Cardiovascular Outcome                                         26

2.14. Ankle Brachial Index and Stroke                                                                      28

2.15. Significance of Borderline Ankle Brachial Index Values                                 29

2.16. Association Between elevated Ankle Brachial Index and Increased Mortality 31

2.17. Primary Care Approach to Subjects with Abnormal Ankle Brachial Index      32

2.18. Contraindications to Ankle Brachial Index                                                       38

2.19. Limitations of Ankle Brachial Index                                                                 38

2.20. Summary from Literature Review                                                                    40

 

CHAPTER THREE

  • Materials and Methods                                                                                    42
    • Study Population                                                                                         42
    • Sample Size                                                                                                43
    • Patients Selection                                                                                        44
    • Study Protocol                                                                                                 44
    • Data Collection                                                                                            47
    • Data Management                                                                                     48

3.8. Ethical Approval                                                                                          48 CHAPTER FOUR

  • Results                                                                                                             49
  • Demographic Characteristics                                                                         49
  • Cardiovascular Risk Factors                                                                         52
  • Prevalence of Intermittent Claudication                                                      62
  • Results of Ankle Brachial Index and Prevalence of Peripheral Arterial Disease 68
  • Profile of Ankle Brachial Index among the Study Population                    70
  • Risk Factors for Low Ankle Brachial Index                                                 74
  • Discussion of Results                                                                                     76
  • Limitations                                                                                                 84
  • Conclusion                                                                                                 85

Recommendations                                                                                                      86

References                                                                                                                  87

CHAPTER ONE

1.0.                                               INTRODUCTION

Adverse cardiovascular events such as Acute Myocardial Infarction and Stroke are emerging as major public health issues worldwide. This is due to the fact that cardiovascular diseases (CVDs) are major causes of morbidity and mortality worldwide. It has been projected that by the year 2020 CVDs will account for 36% of causes of mortality all over the world from the

28% it was in 19901.  Conversely infections as the cause of mortality will decline from 34% to 15% during the same period1. Thus their prevention and early diagnosis is a key objective in primary care.

The underlying pathology in majority of cases is atherosclerosis which is a chronic progressive systemic disease of multifactorial aetiology including hypertension, diabetes mellitus and cigarette smoking as modifiable risk factors and age and sex as non-modifiable risk factors2. These factors have been included in prediction tables to facilitate detection of population at high risk of developing adverse cardiovascular events3. However, the sensitivity and positive predictive value of these tables is low, and thus, most cardiovascular events occurred in individuals without a high risk3.  In addition, atherosclerosis remains clinically silent during most of the evolutionary process until the phenomena of complications of atheroma plaques suddenly appear and lead to ischaemic vascular events4, 5.

Consequently, from a primary prevention point of view, it is very important to have a simple clinical tool which allows identification of patients with atherosclerosis in subclinical stages, with primary care being the optimum setting for accessibility.

The earliest clinical manifestation of atherosclerosis is lower extremity peripheral arterial disease (PAD), which usually occurs before the adverse cardiovascular events5. In other words, the presence of PAD is an indication of generalized atherosclerosis and predicts future adverse cardiovascular outcomes4, 6.

Individuals with PAD have three to fourfold increased risk of CVDs morbidity and mortality compared to individuals without PAD6. The relatively easy access to peripheral circulation allows early identification of asymptomatic individuals, thus allowing taking preventive measures against serious brain and heart clinical atherosclerotic disease. Despite this acknowledged clinical usefulness, the diagnosis of PAD is often not considered during cardiovascular assessment of patients7.

Detection of PAD requires screening with medical history to identify the risk factors, elicit the symptom of Intermittent Claudication (IC) which is the classical symptom of PAD, physical examination of peripheral pulses and the use of some diagnostic procedures4, 5.

The traditional approach to diagnosis of PAD is by establishing the presence of Intermittent Claudication (IC) which is defined as pain experienced in the calf region clearly precipitated by exertion and relieved by rest4, 8.

This approach has been established to be unreliable in assessing the true burden of PAD even among patients with risk factors. This is due to the fact that up to 90% of patients with PAD are asymptomatic7, 8.

Palpating for the peripheral pulses is another widely used method for detecting PAD but has the disadvantage of poor sensitivity for early detection of the condition9.

The ankle brachial index had been demonstrated as the most effective tool in the early diagnosis of PAD10. Compared with angiography, ABI of ≤0.9 presents a sensitivity of 95% and a specificity of 99% for the detection of stenosis 50% or more4, 11.

ABI has also been established as a biomarker of generalized atherosclerosis and cardiovascular risk12. Having a low ABI ratio is an independent risk factor for cardiovascular disease including fatal and nonfatal complications13.

Despite these enormous benefits of ABI, there is paucity of data regarding its use in clinical practice in Nigeria hence the need for this study.

1.1 GENERAL OBJECTIVE

To determine the pattern of ABI among adults attending General Out-Patients’ Clinic (GOPC) of Olabisi Onabanjo University Teaching Hospital (OOUTH), with a view to determining the prevalence of PAD. 

1.2 SPECIFIC OBJECTIVES

  • To establish baseline ABI among adults visiting the GOPC of OOUTH.
  • To determine the prevalence of PAD among adults attending GOPC of OOUTH

Sagamu using the ABI

  • To determine the risk factor(s) for low ABI.

PROFILE OF ANKLE BRACHIAL INDEX AMONG ADULT PATIENTS ATTENDING GENERAL OUT-PATIENTS’ CLINIC OF OLABISI ONABANJO UNIVERSITY TEACHING HOSPITAL SAGAMU

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