Right ventricle diastolic function in high-normal and mildly elevated arterial blood pressure

Introduction

Arterial systemic hypertension may determine impairment of both left ventricle (LV) diastolic and systolic functions, due to increased after load (1). Also the right ventricle (RV) might be involved in this process by structural and functional abnormalities (2). Left ventricular hypertrophy is often associated with hypertension and is an adaptive mechanism to maintain or normalize wall stress, sometimes at the expense of diastolic and long-axis systolic function (3). This adaptive mechanism is associated with changes in left ventricular parameters and in chamber dimensions, geometry and function. These changes are progressive and can ultimately lead to heart failure with systolic and/or diastolic dysfunction (4). Human heart functions as a unit that includes the right ventricle. The spectrum of changes in structure, function and shape of the left ventricle ultimately has an effect on the structure and function of the RV (5).

Only a few publications concern echocardiographic assessment of the RV diastolic function in systemic hypertension, which is all more surprising as physical examination often demonstrates the features of RV pathology and dysfunction in hypertensive patients (6). Purpose of the study was assessment of RV diastolic function in patients with untreated systemic hypertension using conventional and doppler echocardiography.

Study Design

The study was carried out at the echocardiography laboratory of cardiovascular department at Cairo University hospitals. The Research Ethics Committee of the hospital reviewed and approved the study protocol. Fifty seven adult participants aged 54.8±14 years old with high-normal and mildly increased arterial blood pressure never treated with antihypertensive medications were compared with 20 age and gender matched control subjects .Patient written consent was given by all the participants. Hypertension was defined as persistent elevation of blood pressure above 140/90 mmHg on two or more occasions with the patient in a sitting position for at least five minutes (7). Patients were subjected to history taking, physical examination and simple clinical investigations. Demographic parameters, including age, gender and associated symptoms were obtained. Subjects with ischemic heart disease, valvular heart disease and cor pulmonale were all excluded.

Echocardiography

All subjects had echocardiography performed with the use of a Philips IE 33 (Andover, MA, USA) Ultrasound according to recommendations of the American Society of Echocardiography (8). Left ventricle structure, dimensions and functions were studied. Right ventricle wall thickness was measured in diastole from the sub costal views wall and wall thickness ≥ 5 mm indicates RV hypertrophy (9). Right ventricle diastolic function was assessed by recording tricuspid flow with standard pulsed wave Doppler and by measurements of early diastolic peak flow velocity (E), late diastolic peak flow velocity (A) and the ratio of early-to-late flow velocity peaks (E/A ratio).

Tissue Doppler imaging (TDI)

In the apical four-chamber view, the sample volume was placed at the lateral tricuspid annulus to study early diastolic (E') and late diastolic (A') velocities. The use of E':A' ratio is one of the recommended indices approved by the American Society of Echocardiography for assessing right ventricle diastolic dysfunction (8, 10).

Statistical analysis

All statistical calculations were done using computer program SPSS (Statistical Package for the Social Science, SPSS Inc., Chicago, IL, USA) release 15 for Microsoft Windows (2006). All Data were statistically described in terms of mean ± standard deviation (± SD) Comparison of numerical variables between the study groups was done using Student t test for independent samples and one way analysis of variance (ANOVA) test when comparing 3 group. P-value less than 0.05 was considered statistically significant.

Results

Fifty seven participants aged 54.8±14 years old (40 females and 17 males) with high-normal and mildly increased arterial blood pressure never treated with antihypertensive medications were compared with 20 age and gender matched control subjects free of any cardiac diseases. Systolic (SBP) and diastolic blood pressures (DBP) were significantly higher in hypertensive subjects compared to the controls (143.7±2.7 and 93.2±5.1 mmHg vs 119.4±8.1 and 72.3±6.9 mm hg, p-value <0.001 for both)(Table-1).

Conventional Echocardiography

Interventricular septum thickness and right ventricle free wall thickness were significantly increased in patients with mild untreated systemic hypertension (1.2±0.2 and 0.5±0.1 vs.0.8±0.1 cm and 0.28±0.1cm among control group, P<0.001for both).

Pulsed and tissue Doppler imaging

Mitral E/A ratio 1.2±0.1 and 0.7±0.1 in the control and hypertensive group respectively (P value < 0.001). While, tricuspid E/A was 1.3 and 0.9 in control and hypertensive groups respectively. Tissue Doppler tricuspid E' and E'/A' values were significantly decreased in hypertensive group (12±3.1 cm/s and 0.8 ±0.2 vs 15.3 ±1.3 cm/s and 1.2±0.1 in control group, p <0.001 for both) (Figure-1).Positive significant correlation was found between mitral and tricuspid E/A ratio (p<0.001, r: 0.842). Univariate regression analysis revealed that body mass index was found to be significant predictor of RV diastolic dysfunction (p:0.023).

Discussion

It was found that in middle-aged men central distribution of body fat is associated with increased BP, independently of body mass index and insulin resistance, thus suggesting a key role of central adiposity in the full expression of the “metabolic syndrome (11). The current study showed that body mass indices and waist circumferences were increased in the hypertensive group. Moreover, body mass index was found to be significant predictor of RV diastolic dysfunction (RVDD). This is concordant with other studies that found that mitral annular E':A' ratio and body mass index were the only predictors of RVDD (10). Concordant with other studies (12), the present study used the ratio E':A' ratio alone to assess RVDD . However, this index was approved by the American Society of Echocardiography to assess the global RV diastolic function. Positive significant correlation was found between mitral and tricuspid E/A ratio (p<0.001, r: 0.842) this is in accordance with other study that assessed RV DD in 100 adult Nigerian hypertensive subjects (13).

Concordant with some studies that found that the prevalence of RV hypertrophy consistently varied among studies (17.0-80.0%) with an average of 28.6% in the pooled population (14), the current study found that RV hypertrophy was prevalent in 28% of the high-normal and mildly increased blood pressure group. It was found that RV diastolic and systolic function deteriorates in response to slightly increased systemic BP (15). It was found that increased pulmonary vascular resistance in systemic hypertension results from the activation of vasoconstriction pathways in both systemic and pulmonary vascular beds which may explain right ventricular hypertrophy from mild to moderate, uncomplicated hypertensive patients (16).

Moreover, combination of increased thickness of the posterior wall, inter ventricular septum dimensions and right ventricular wall thickness will ultimately lead to at least progressive reduction in the right ventricular end-diastolic dimensions before progressive dilatation may occur in the right heart (17).

A magnetic resonance imaging study to assess RV remodeling in systemic hypertension revealed that that systemic hypertension was associated with concentric RV remodeling and impaired diastolic function, confirming that the unstressed ventricle is not immune to the effects of systemic hypertension (18).

Conclusion

In arterial hypertension, increased systemic after load is transferred to RV, a structure not directly exposed to systemic BP but the inter ventricular septum is likely the candidate for that role. Right ventricle diastolic function could provide novel insights in RV function impairment in high-normal and mildly increased arterial blood pressure. Moreover, RV diastolic dysfunction may be an early clue to hypertensive heart disease.