International Journal of Cardiovascular ResearchISSN: 2324-8602

All submissions of the EM system will be redirected to Online Manuscript Submission System. Authors are requested to submit articles directly to Online Manuscript Submission System of respective journal.

Research Article, Int J Cardiovas Res Vol: 6 Issue: 2

Angiotensin II as an Indicator of Left ventricular Hypertrophy in Uncontrolled Treated Hypertensive Patients

Tamer M Abu Arab*, Moustafa El Nozahi, Wessam Wahid and Hany F Hanna
Department of cardiology, Faculty of medicine, Ain Shams University, Cairo, Egypt
Corresponding author : Dr. Tamer M Abu Arab
Department of Cardiology, Faculty of medicine, Ain Shams University, Lotfy El-sayed st., Abbasia square, Cairo, Egypt, Postal code- 11566, Egypt
Tel: +201006004924
Fax: 0020224820416
E-mail: [email protected]
Received: December 19, 2016 Accepted: February 15, 2017 Published: February 20, 2017
Citation: Abu Arab TM, El Nozahi M, Wahid W, Hanna HF (2017) Angiotensin II as an Indicator of Left ventricular Hypertrophy in Uncontrolled Treated Hypertensive Patients. Int J Cardiovasc sRes 6:2. doi: 10.4172/2324-8602.1000305

Abstract

Background: left ventricular hypertrophy (LVH) in uncontrolled hypertension is a major risk factor and the mechanism is not fully understood weather it is due to increased afterload or due to an angiotensin II (Ag II) mediated action on the heart. Objectives: we studied the relationship between Ag II serum level and concentric LVH in patients with hypertension. Methods: a total of 91 patients were included, all had long standing (≥ 5 years) essential uncontrolled treated hypertension and were categorized into two groups according to presence of concentric LVH by echocardiographic criteria (LV mass index (LVMI)>115 g/ m2 for men, LVMI>95 g/m2 for women and relative wall thickness (RWT)>0.42). Group I had 47 patients with LVH and group II had 44 patients without LVH. Ag II serum level was measured in all of them. Results: Ag II serum level was higher than normal range in all patients in both groups (cutoff value was taken as 30pg/ml). It was significantly higher in patients with LVH (group I) with mean level 70 pg/ml compared to 43 pg/ml in patients without LVH (group II) (p=0.000). In patients with LVH, Ag II serum level had positive correlation with BMI (r=0.325, P=0.026) but it had no correlation to age, gender, diabetes, duration of hypertension and, surprisingly no correlation to severity of LVH. Conclusion: Patients with LVH have higher serum level of Ag II compared to patients without LVH but it cannot be considered as the only causative factor for LVH in hypertensive patients and other factors should be considered.

Keywords: Angiotensin II; Hypertension; Left ventricular hypertrophy

Keywords

Angiotensin II; Hypertension; Left ventricular hypertrophy

Introduction

Hypertension is a common health problem worldwide; especially in developing countries, it has a large health burden owing to its long term cardiovascular complications [1]. Hypertension is defined as a value ≥ 140 mmHg Systolic BP (SBP) and/or ≥ 90 mmHg diastolic BP (DBP) and these cut off values are universal [2].
Hypertension can be either primary (essential hypertension) or secondary to any other medical disease. Essential, primary, or idiopathic hypertension is defined as high BP in which secondary causes such as reno-vascular disease, renal failure, pheochromocytoma, hyperaldosteronism, or other causes of secondary hypertension are not present [2], long standing uncontrolled hypertension which can be either primary or secondary is one of the major risk factors for multi-organ failure especially left ventricular hypertrophy which is a major risk factor for coronary artery disease and congestive heart failure [3].
Left ventricular hypertrophy (LVH) is defined as an increase in the mass of the left ventricle, which can be secondary to an increase in wall thickness (Concentric LVH) or an increase in cavity size (Eccentric LVH) or both. Echocardiography is one of the most used methods for detection of LVH and proper calculation of the LV mass [4].
The control of arterial blood pressure depends on a complex interaction of many factors neural, endocrine and metabolic and these components maintain a balance between vasoconstrictor and vasodilator substances from which the most important is the reninangiotensin system [5,6], its actions on blood vessels are complex. It acts as an endocrine system and as a local tissue hormonal system through its paracrine and autocrine effects and it act as a neuromodulator, particularly of sympathetic actions on vascular smooth muscle [7].
Few researches have showed that there is a direct relationship between angiotensin II level and occurrence of LVH especially in long standing uncontrolled hypertension. Angiotensin II in addition to its vasoconstrictor and aldosterone-stimulating action, it also drives cell growth and replication in the cardiovascular system which may result in myocardial hypertrophy and hyperplasia [8]. This study was conducted to study the relationship between serum level of angiotensin II and presence of concentric LVH in patients with long standing (five years or more) essential uncontrolled treated hypertension.

Methods

Study subjects
This study was conducted on 91 hypertensive patients who were referred to our center for echocardiography from July 2015 to December 2015. All the patients included in the study had long standing (five years or more) essential hypertension, all were receiving medical treatment and their blood pressure (BP) were uncontrolled. BP was measured in 2 different visits at least 2 weeks apart with complete physical and mental rest for at least 10 minutes and 2 readings were taken by 2 different operators 15 minutes apart. BP and was considered uncontrolled when systolic BP ≥ 140 and diastolic BP ≥ 90 mmHg in both readings and both visits [9].
The patients were categorized into 2 groups according to echocardiographic criteria of concentric LVH. Group (1) included 47 patients with concentric LVH (LV mass index >115 g/m2 for men, LV mass index>95 g/m2 for women) [10,11], while Group (2) included 44 patients without concentric LVH.
Patients with known or suspected secondary hypertension, patients with decompensated heart failure and patients with other causes of LVH (aortic stenosis, hypertrophic cardiomyopathy, infiltrative cardiomyopathy, subaortic membrane) were excluded from the study.
The study was approved by the local ethics committee; as it conforms to the ethical guidelines of the 1975 Declaration of Helsinki, as revised in 2013 and all patients signed a written informed consent for laboratory assessment.
Study methods
Patients were subjected to the full medical history regarding age, risk factors, duration of hypertension and past history of any medical condition that may lead to secondary hypertension (e.g.: chronic kidney disease, renal artery stenosis, thyroid disease, steroid therapy and females on oral contraceptive pills). Detailed history of antihypertensive medications that patients were receiving was considered including number of medications and their classes.
Arterial blood pressure was measured manually from the right upper limb at the level of the heart using a mercury sphygmomanometer while patient is sitting down after complete physical and mental rest for 10 minutes [12] with the measurement was repeated after 15 minutes by different operator. The blood pressure measurement was repeated with the same precautions after at least 2 weeks.
Signs of decompensated heart failure (congested neck veins, bilateral lower limb edema and basal rales), and systemic manifestation of any endocrinal disturbance (moon face, exophthalmos, thyroid goiter, abdominal bruit) were watched for exclusion.
For every patient: weight was measured in Kilograms and height was measured in meters to calculate the body mass index (BMI) and body surface area (BSA). BMI = weight (kg)/ Height2 (m2) [13], BSA= 0.007184 x W0.425 x H0.725 [14].
Echocardiographic assessment
Comprehensive 2D, M-mode and Doppler echocardiography were performed by a specialist for all patient using (GE Vivid 7, Ultrasound system) with special focus on Left ventricular dimensions which were all measured using M-mode using the leading-edge–to–leading-edge technique allowing for accurate calculation of the LV mass [15,16].
The dimensions measured were: Interventricular septal thickness measured at the end of diastole (IVSD), posterior wall thickness measured at the end of diastole (PWD), left ventricular end-diastolic diameter (LVEDD), Left ventricular end-systolic diameter (LVESD) and relative wall thickness (RWT).
Left ventricular mass index (LVMI) was calculated using the American Society of Echocardiography (ASE) formula incorporated in the GE machine which correlates the LV mass with the body surface area (BSA).
LV mass = 0.8 (1.04 ([LVEDD + PWTD + IVSTD]3 - [LVEDD]3))+ 0.6 in grams [10].
LVMI = LVM/ BSA [10,11].
LVH was defined as LVMI>115 g/m2 for men, LVMI > 95 g/m2 for women [10,11].
The ejection fraction (EF) was also calculated using M-mode.
Laboratory investigations
Routine laboratory work up was done including measurement of serum creatinine, Sodium, Potassium, TSH to exclude secondary hypertension.
Measurement of Serum Angiotensin II level: a venous blood sample was taken from all the patients and collected in serum separating tubes and then was centrifuged within 15 minutes from obtaining the sample using a centrifugator at angular speed of 3,000 RPM for 10 minutes to separate the serum. Then the serum was stored in a -2°C freezer till the time of analysis.
Angiotensin II serum level was measured using a customized laboratory kit bought from “Assay Pro” company located in Missouri (USA) which was shipped to us. The kit had an expiry date at 31 January 2018 and was valid for 6 months from the date of usage.
The kit contained: A Human Angiotensin II Microplate: A 96- well polystyrene microplate coated with polyclonal antibodies against Ag II, sealing Tape, Human Angiotensin II standard: A 6 ng buffered lyophilized protein, biotinylated Human Angiotensin II Antibody: Polyclonal antibody against Ag II and other chemicals.
Angiotensin II was measured using enzyme-linked immunosorbent assay (ELISA) which employs a quantitative sandwich enzyme immunoassay. The tests were done in a specialized laboratory by a specialized laboratory technician.
Assay procedure
Preparation of the standard stock solution (2 ng/ml) was done by mixing Human Ag II standard with 3 ml of EIA diluent to generate the 2 ng/ml standard stock. Then Serial dilution of the standard stock solution 1:2 with equal volumes of EIA Diluent to produce (1),(0.5),(0.25),(0.125) and (0.0625) ng/ml solutions which will serve as the 5 standard solutions for the standard curve for the remaining 91 wells in the microplate. Then the collected serum of each of the 91 patients was added to each of the 91 remaining wells in the microplate and all wells were covered with sealing tapes and incubated for 2 hours.
Normal serum level of Angiotension II is ≤ 30 pg/ml and any value exceeding 30 pg/ml was considered a high value [17].

Statistical Analysis

Data were collected, revised, coded and entered to the Statistical Package for Social Science (IBM SPSS) version 20. Qualitative data were presented as number and percentages while quantitative data were presented as mean, standard deviations and ranges. The comparison between two groups with qualitative data was done by using Chi-square test and/or Fisher exact test (used instead of Chisquare test when the expected count in any cell was found less than 5). The comparison between two independent groups of quantitative data with parametric distribution was done by using Independent t-test. Spearman correlation coefficients were used to assess the relation between two quantitative parameters in the same group. The confidence interval was set to 95% and the margin of error accepted was set to 5%. So, the p-value was considered significant as the following: P>0.05: Non significant, P<0.05: Significant and P<0.001: Highly significant.

Results

The study included 91 patients with uncontrolled, essential and treated hypertension. 47 patients had LVH by echocardiographic criteria (Group I) and 44 patients didn’t have LVH (Group II). Patients in group I were younger with mean age of 53.57 ± 7.37 than patients in group II with mean age of 58.57 ± 9.33 (P=0.006), other basic characteristics including gender, presence of diabetes, anthropometric data, duration of HTN, BP readings and antihypertensive medications were well balanced in both groups (Table 1).
Table 1: Basic characteristics of the study population.
Patients in both groups showed normal LV dimensions with preserved EF and of course by study design, patients in group (I) showed a significantly higher IVS thickness, PW thickness, relative wall thickness (RWT) and LVMI than patients in group II (P=0.000). Mean RWT was 0.51 in LVH group indicating that patients had concentric LVH. In group I, males had a mean LVMI of 133.36 gm/m2 while it was 122.29 gm/m2 for females while in group II patients had a mean LVMI of 88.25 gm/m2 and 74.3 gm/m2 for males and females respectively (Table 2).
Table 2: Echocardiographic data.
Measured serum Ag II level was found to be higher than normal range in all patients in both groups but was significantly higher in patients with LVH (Group I) with mean level of 70.21 pg/ml compared to 43 pg/ml in patients without LVH (p=0.000). Also in group I patients who have high above normal Ag II level (76.6%) were significantly more than patients who have high value (50%) in group II (P=0.008) (Table 3) (Figure 1).
Figure 1: Angiotensin II serum concentration in group (I) and group (II).
Table 3: Laboratory data.
The high serum Ag II level in patients with LVH seemed to be not affected by type or number of antihypertensive medication except patients who received angiotensin receptor blockers (ARBs) who showed no difference in the value of Ag II level in both groups (P=0.977) (Table 3).
Using Spearman correlation coefficients to assess the relation between Ag II level and other parameters in patients with LVH, it was found that weight and BMI had a direct correlation with Ag II serum level. Overweight and obese patients with LVH had the highest Ag II serum level (80.53 pg/ml and 73.57 pg/ml respectively). In group II this correlation was not observed. Serum Ag II level had no correlation to age, gender, diabetes, duration of hypertension and, surprisingly no correlation to severity of LVH (Table 4) (Figures 2 and 3).
Figure 2: Fitted line plot for Regression coefficient of Ag II and body weight.
Figure 3: Fitted line plot for Regression coefficient of Ag II and BMI.
Table 4: Correlation between Ag II serum concentration and other parameters in patients with LVH (group I).

Discussion

Left ventricular hypertrophy (LVH) is one of the most common long term complications of hypertension known as end-organ damage and related to worse outcome of coronary artery disease, myocardial infarction, atrial fibrillation, congestive heart failure and cerebrovascular stroke [4]. Left ventricular hypertrophy (LVH) is defined as an increase in the mass of the left ventricle, which can be due to an increase in wall thickness which is called “Concentric LVH” where relative wall thickness >0.42, or an increase in cavity size which is called “Eccentric LVH” where Relative wall thickness <0.42. LVH is diagnosed mainly by echocardiography [18,19]. Understanding the mechanism of LVH and preventing its occurrence may help in decreasing cardiovascular risk of hypertension.
The control of arterial blood pressure depends on a complex interaction of many factors, neural, endocrine and metabolic. And these components maintain a balance between vasoconstrictor and vasodilator substances. The most important and the most studied system is the Renin-Angiotensin Aldosterone system (RAAS) which consists of Angiotensinogen, Renin, Angiotensin I, Angiotensin converting enzyme (ACE), Angiotensin II (Ag II) and Angiotensin II receptors (AT I and AT II) [20,21].
Angiotensin II is a vasoconstrictor which causes an increase in total peripheral vascular resistance and thereby increasing left ventricular afterload, intramyocardial wall tension and myocardial oxygen demand. Its intermediate action is through its stimulation of aldosterone release which acts as an anti-natriuretic and antidiuretic agent [22]. Its long-term action is through the regulation of the expression of genes that activate and drive cell growth and replication in the cardiovascular system [22].
Although the relationship between Ag II and development of LVH is common knowledge based on all we know about the actions of Ag II, few recent studies have focused on this relationship and most of them were animal studies.
Our study was conducted on 91 patients with essential uncontrolled hypertension although receiving medical treatment. Those patients were classified according to presence of LVH by echocardiographic criteria [10] into two groups. Group (I) included 47 patients with concentric LVH while Group (II) included 44 patients without concentric LVH. Serum Ag II level was measured for all patients in both groups by ELISA. Serum Ag II ≥ 30 pg/ml was considered an abnormally high value [17]. The major aim of the current study was to evaluate the level of Ag II in relation to LVH. Interestingly, it was above upper normal in all patients with hypertension whether they had LVH or not but its level was significantly higher in patients with hypertrophy. One might thus speculate that there is a threshold level above the upper normal which triggers the mechanisms of LVH. However, when we tested for the correlation, the severity of LVH was not correlated to the level of Ag II (r=0.178, p=0.231).
Saiki et al. in 2009 conducted a study to investigate serum Ag II in obese patients with type 2 diabetes mellitus (T2D) and the change during weight loss in 50 Japanese obese subjects with T2D (body weight, 75.0 ± 14.1 kg, BMI, 29.1 ± 3.7 kg/m2). The subjects were prescribed a diet of daily caloric intake of 20 kcal/kg for 24 weeks. Serum Ag II was measured before and after 24 weeks. After 24 weeks of weight reduction diet, the mean body weight decreased by 2.3% and the mean serum Ag II decreased by 24% (P<0.0001) and correlated significantly with body weight both at baseline (r=0.425, P=0.0018) and at 24 weeks (r=0.332, P=0.0181) [23], this study showed that serum Ag II was correlated with body weight and BMI decreasing during weight loss. In support, our study showed positive correlation between each of BMI and body weight on one hand and Ag II on the other, only in hypertensive patients with LVH (thus with higher Ag II levels).
A recent human study was conducted in 2015 on renal transplant recipients to evaluate the relationship of local intrarenal RAS with LVH, The study was conducted on 96 normotensive and hypertensive renal transplant recipients and urinary angiotensinogen level was measured and it was found to be significantly higher in hypertensive patients compared with normotensive patients (p<0.01). LVMI was also significantly higher in hypertensive patients compared with the normotensive patients (p<0.01) indicating a significant positive correlation between urinary angiotensinogen levels and LVMI (r=0.724, p=0.012) [24].
Several animal experiments were held to demonstrate that Ag II had receptor-mediated effects on stimulating cardiac hypertrophy independent of mechanical stimuli (increased cardiac after load) in adult rats. Ag II was infused into Sprague-Dawley rats for 14 days and control rats were infused with normal saline. Ag II infused rats showed a significantly increased left ventricular mass index in comparison to control rats. The progression of LVH was successfully blocked using Ag II receptor antagonist (ARB) while blockade of converting enzyme with enalapril maleate and treatment with a vasodilator had no effect on the All-induced hypertrophy [25]. This study showed that Ag II induces cardiac hypertrophy through its action on AT1 angiotensin receptors which can occur regardless of the cardiac afterload. This may explain partially why in our study patients on ACEI showed no difference in LVH and Ag II level which could be due to alternative pathways of Ag II production (Non ACE dependent) like Chymase pathway [26]. This also explains that treatment by ARBs may help in prevention and regression of LVH more than ACEI. This was not evident in our study mostly due to low number of patients who received this expensive type of treatment (only three patients in group (I) and four patients in group (II)) in a government hospital visited by patients with lowest income. However, it has to be mentioned that, based on our results, there was no advantage of any group of the antihypertensive drugs in prevention of LVH where all drugs were equally distributed in both groups. In addition to LVH, drugs known to affects the RAAS, including B blockers, ACEI, ARBs and diuretics, had no significant relationship to Ag II level in this trial.
Another animal study showed the effect of Ag II on renal receptors and its effect on hypertension and LVH. This study used a kidney cross-transplantation strategy carried out between wild-type mice and mice homozygous for a targeted disruption of the gene location locus encoding the AT1A receptor. This strategy helped to generate four groups of animals. 2 groups had renal AT1A and lacked the receptors in the heart (systemic knockout), while 2 groups had cardiac AT1A receptors and lacked these receptors in the kidneys (kidney knockout). After Ag II infusion, the first 2 groups showed an increase in BP and LVH while the other 2 didn’t show any evidence of LVH after Ag II infusion [27]. The previous study showed that cardiac AT1 receptors are not necessary for the development of hypertrophy and that prolonged stimulation of AT1 receptors in the heart, without blood pressure elevation, is not sufficient to cause cardiac hypertrophy in vivo. The mechanism of LVH in patients with hypertension whether controlled or uncontrolled is still not fully understood even with high serum level of Ag II (i.e. Ag II is not the only factor). Other mechanisms or hypothesis for the development of LVH should be considered and may be related to renal mechanism and this was clear in the last study which showed that only rats with renal AT1 receptors developed LVH in comparison to rats with only cardiac AT 1 receptors.
The history is so deficient in human trials, both cross sectional and interventional drug trials. Thus it is so hard to compare to the available studies or make definite conclusions from the data so far found, especially as we see points of disagreement are more than points of agreement. Unresolved points are many, so further studies are needed to completely understand the mechanism of development of LVH in hypertensive patients.

Study Limitation

The study is a single center study and included only uncontrolled hypertensive patients. Limited number of patients was on ARBs treatment which was an obstacle to show any relation between ARBs use and LVH and serum Ag II level. In our study we used two reading methods for assessment of uncontrolled hypertension instead of the more accurate ambulatory blood pressure monitoring due to lack of availability during the entire time of the study.

Conclusion

Patients with LVH have higher serum level of Ag II compared to patients without LVH, this is not affected by age, sex, duration of blood pressure nor medications. In spite of high serum level of Ag II and its important relation to LVH in hypertensive patients, it can’t be considered as the only causative factor for LVH and other factors should be considered.

References

Track Your Manuscript

Scheduled supplementary issues

View More »

Media Partners