CADENA DE VALOR

Complications of systemic hypertension could be acute or chronic.

The acute complications of systemic hypertension are hypertensive encephalopathy, acute left ventricular failure, acute renal failure, aortic dissection and pre-eclampsia.

Chronic complications of systemic hypertension include - hypertensive heart disease, heart failure, coronary artery disease, cerebrovascular disease, hypertensive retinopathy, hypertensive induced peripheral neuropathy especially in association with diabetes mellitus, hardening of the arteries (involutional arteriosclerosis), acceleration of atheromatosis, dissecting aortic aneurysm, chronic kidney disease (hypertensive nephrosclerosis), sudden cardiac death and hypertension in pregnancy.

2.7.1 HYPERTENSIVE HEART DISEASE

Systemic hypertension can lead to changes in the coronary vessels, conduction system of the heart and myocardial structure.

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It manifests clinically as hypertensive heart disease with or without heart failure, left ventricular hypertrophy, left ventricular diastolic and systolic dysfunction, and coronary artery disease.

The interplay between systemic hypertension and the elucidated cardiovascular risk factors contributes to the onset and/or progression of these clinical manifestations.

2.7.2 LEFT VENTRICULAR HYPERTROPHY (LVH)

LVH is defined as an increase in the mass of the left ventricle (LV) and is caused by the response of myocytes to various stimuli accompanying elevated BP.

An increase in LV thickness and LV mass with increased LV diastolic pressure and volume, commonly observed in systemic hypertension is known as concentric LVH, and this is a marker of poor prognosis in the presence of systemic hypertension. LVH in systemic hypertension is an adaptive response to the increased afterload, and therefore serves to normalize wall stress.

Abnormalities of diastolic function occur as a consequence of both systemic hypertension and LVH⁵⁸.

Important factors predisposing to LVH include age, BP, and obesity⁵⁸. LVH is more prevalent in women and Blacks than in men and Whites.⁵⁹

BP is the most important determinant of LVH, irrespective of whether a diagnosis of systemic hypertension is established by office and/or home measurements, or by ambulatory BP monitoring⁶⁰.

LVH is an independent risk factor for the development of heart disease in systemic hypertension.

Studies in hypertensive subjects show that recordings from ambulatory blood pressures monitor (ABPM) correlates better with LV mass than clinic blood pressure measurements⁶¹.

Impaired exercise performance in African hypertensive patients has been noted to occur with the onset of left ventricular hypertrophy and may be a prelude to adverse outcomes⁶².

Left ventricular hypertrophy is present in 25% of hypertensive patients and can easily be diagnosed by echocardiography⁶³. Other methods of assessing LVH, though with varying sensitivity and specificity include - ventriculography, roentgenography, electrocardiography (ECG) and computed tomography or echocardiography. Echocardiography is the most accurate and reliable non-invasive diagnostic method for assessing LVH though ECG services and roentgenography are more readily available in Nigeria.

Araoye⁶⁴ in a study on ‘Left Ventricular Hypertrophy by Electrocardiography’ developed diagnostic criteria for LVH applicable to Negroes as shown below:

14 Araoye Criteria

SV2 + RV6 > 40mm in men SV2 + RV6 >35mm in women RI >12mm

Strain pattern in V5 or V6.

Another criterion for diagnosing LVH is Sokolow-Lyon Criterion⁶⁵. (SV1+RV5 or V6 >35mm)

2.7.3 LEFT VENTRICULAR DIASTOLIC DYSFUNCTION

Left ventricular diastolic dysfunction refers to an abnormality of left ventricular filling during the various stages of diastole. Left ventricular diastolic dysfunction may result from increased myocardial stiffness or impaired relaxation. Relaxation can be slowed, decreasing early diastolic filling, or incomplete, which impairs filling throughout diastole and decreases end-diastolic distensibility.

The classic presentation of diastolic dysfunction is “flash pulmonary edema,” in which resting LV ejection fraction is norma⁶⁶.

Isolated systolic hypertension is more common in women and is a major risk factor for diastolic heart failure which is also more common in women⁶⁷. Diastolic dysfunction is often categorized as grades 1 through 4.

Grade 1- Mild diastolic dysfunction (impaired relaxation pattern).

Grade 2- Moderate diastolic dysfunction (pseudonormal pattern).

Grade 3- Severe reversible diastolic dysfunction (restrictive pattern reversible by Valsalva manoeuvre).

Grade 4- Severe irreversible diastolic dysfunction (restrictive pattern irreversible by Valsalva manoeuvre). Table 1 shows the summary of diastolic function.

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TABLE 1: SUMMARY OF DIASTOLIC FUNCTION

Normal Grade 1

(Delayed relaxation)

Grade 2

(Pseudonormal)

Grade 3 or 4 (Restrictive)

E High Low High

E/A >1 <1 >1 >2

IVRT(ms) 60-100 >100 60-100 <60

DT (ms) 160-240 >240 160-240 <160

Tissue Doppler septal e’(cm/s)

>10 <10 <10 <8

Pulm. Vein SD ratio

>1 >>1 <1 <1

LA pressure Normal Normal Moderately

Elevated

High

KEY: E= early diastolic filling, A= late diastolic filling, IVRT= isovolumic relaxation time, DT= deceleration time, LA= left atrial, e’= early diastolic velocity of the mitral annulus, S=

systolic forward pulmonary vein velocity, D= diastolic forward pulmonary vein velocity.

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2.7.4 LEFT VENTRICULAR SYSTOLIC DYSFUNCTION

Left ventricular (LV) systolic performance is reflected in the efficiency of the left ventricle to pump blood in systole. Thirty to forty percent of heart failure patients have normal systolic function⁶⁸. Study done by Balogun et al⁶⁹ reported that 50-53% had impaired relaxation while 10-38% had restrictive diastolic function. The normal reference value for left ventricular ejection fraction (EF) and fractional shortening (FS) are >50% and >20% respectively⁷⁰. During the cardiac cycle, the dimensions and shape of the heart chamber change in conformity with the different phases. Examples include LV internal volume in systole and diastole (LVESV= 35±

5ml, LVEDV=85±15ml), LV internal dimension in systole and diastole (LVESD= 24-42mm, LVEDD=36-52mm), LV wall thickness in diastole (IVSD=6-12mm, LVPWD=6-11mm), LV wall excursion in systole (IVSS= 6-9mm, LVPWS= 9-14mm) ⁷¹.

Up till about 37 years ago, hypertensive heart disease (HHD) was referred to in many literature as “Cardiomegaly of unknown origin” until Falase⁷² drew our attention to the role of systemic hypertension in its aetiology. Following that, Araoye et al⁷³ in a study on “The Clinical spectrum of Hypertensive Heart Failure” established that HHD culminating in HHF presents in a spectrum or stages:-

Stage 1:- in which the patient presents with heart failure coexisting with systemic hypertension, thus making a cause-and-effect relationship questionable. Even though in failure, the heart at this stage is still viable enough to support HBP.