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CHAPTER FIVE

Secondly, the effect of “White-Coat” hypertension on the study population could not be completely eliminated though there was an attempt to limit it. The study being a cross-sectional one it is likely that the elevated blood pressure recorded in some subjects at the material time could have been influenced by the excitement and tension associated with the visit to the doctor¹⁴⁸, a seldom occurrence. Ayam and Goldshine in a study of 34 patients with HBP in USA demonstrated that home blood pressure level may be as much as 70/36mmHg lower than clinic or office level⁸⁹.

The third factor will obviously be the lower cut off point now used for the diagnosis of HBP in line with the WHO criteria¹².

Correlating Factors

Both systolic and diastolic blood pressure correlated positively and significantly with age, weight and BMI of all subjects; with SBP showing a better correlation with age than the DBP.

The increase in BP with age agrees with the findings of Akinkugbe and Ojo that in both urban and rural Nigerian BP significantly rose with age but the rise was more in the urban dweller than the rural¹⁴⁹, and with the observations of Kaufamn et al¹⁵⁰ as well as the expert committee on the National Survey of Hypertension in Nigeria²⁴. However, it varies with the report of Cooper et al that in the rural African, blood pressure does not rise with age¹⁵¹. They attributed this to low prevalence of obesity,

moderate salt intake, a diet low in fat, and high levels of physical activity within the rural setting. They were, however, quick to note that any modest shift from these baseline conditions leads to sizeable changes in the risk for hypertension.

Though there was no positive correlation between BP and sex in the study, works in Gambia showed that rural men have higher average blood pressures than women¹⁵². Olatunbosun et al from their study in Nigeria, concluded that the male gender was among the biosocial determinants of hypertension in the urban Black population²⁵. The non-confirmation of the correlation between sex and blood pressure may derive from the small sample size.

ECG Evaluation

Since its inception, ECG has remained the only practical method of recording the electrical behaviour of the heart, has the potential to reflect anatomy, blood flow, haemodynamics, transmembrane ionic fluxes and effect of drugs, each of these often the single goal of other non-invasive techniques¹⁵³.

From the studies there were significant ECG abnormalities between the hypertensive subjects and controls. As shown in table 9, the major abnormalities seen in the hypertensives in the descending order of occurrence were LAE (52%); LAD (32.7%); LVH (28.7%);

prolonged QTc (11.3%. They represent the adaptive and structural damage that can result from long-standing hypertension.

The high prevalence of LAE is understandable because LVH in hypertensive heart disease may be identified initially by ECG using the criteria of LAE. This involvement does not reflect atrial disease primarily but the adaptation of the atria to the reduced compliance or distensibility of the hypertrophying chamber of the left ventricle as diastolic function becomes impaired¹⁵⁴.

Patients with LVH are at increased risk of cardiovascular morbidity and mortality. Although the precise mechanisms responsible for the increased risk are not known, patients with LVH succumb to premature sudden and ischaemic heart-related death and increased number of ventricular arrhythmia¹⁵⁵.

A common factor in the pathogensis of left axis deviation is ischaemia or fibrosis of the left bundle of His¹⁵⁶. While the cause is mainly coronary atherosclerosis in Caucasians, in Nigerians possible aetiological factors include hypertensive heart disease, cardiomyopathy and valvular heart disease¹⁵⁷. Agomuoh and Odia¹⁵⁸ recorded a low prevalence (6%) of left axis deviation in normal adult Nigerians. Packard et al¹⁵⁹ reported left axis deviation in 1.3% of 1000 young and healthy Caucasian aviators showing that left axis deviation is also uncommon among healthy Caucasians; a finding also supported by Araoye¹³⁶. The

21% prevalence found in the control may be accounted for by age; for in all races and both sexes the QRS Axis shifts leftward with age¹³⁸. This is also in consonance with the finding from the study, as shown in Fig. VIII.

QT interval usually varies according to the heart rate, sex and age hence the need for correction (QTc) using the Bazett’s formula. Because of the variability of measurements and potential influences other than heart rate, different ranges of normal are accepted by different investigators. Therefore for practical purposes, minor deviations from the expected QTc interval are disregarded as being of questionable clinical significance¹³⁸. Generally females have longer QTc than males as documented by Araoye¹³⁶, Onwubere¹³⁷ and Agomuoh¹⁶⁰.

From the study, there was significant difference in QTc among hypertensives and control (P =0.02). This agrees with the finding of Araoye et al¹⁶¹ that a significant increase in QTc exists between adult hypertensive when compared with normotensives.

Other abnormalities noted in the study such as 1⁰ AVB, RBBB, sinus bradycardia etc have also been document by other workers in normal healthy adult Nigerians137,138,160,161. The low figures involved could not allow for their tests of significance.