International Journal of Cardiovascular ResearchISSN: 2324-8602

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Research Article, Int J Cardiovasc Res Vol: 3 Issue: 4

Demonstration of Early Endothelial Dysfunction in Diabetics with Normal Exercise Electrocardiogram

Arif Cimen1, Ahmet Ekmekci2, Mahmut Uluganyan3*, Elif Ijlal Cekirdekci2, Fatih Selcukbiricik4, Faizel Osman5, Ali Elitok1, GokhanErtas2, Mehmet Eren2 and Huseyin Oflaz1
1Department of Cardiology, Istanbul University, Istanbul Medical Faculty, Istanbul, Turkey
2Clinic of Cardiology, Dr. Siyami Ersek Thoracic and Cardiovascular Surgery Center Training and Research Hospital, Istanbul, Turkey
3Clinic of Cardiology, Kadirli Government Hospital, Osmaniye, Turkey
4Department of Internal Medicine, Istanbul University, Capa Medicine Faculty Hospital, Istanbul, T Turkey
5University Hospital Coventry, Clifford Bridge Rd, Coventry, CV2 2DX, UK
Corresponding author : Mahmut Uluganyan, MD
Clinic of Cardiology, Kadirli Government Hospital, Sehit Orhan Gok Mah, TOKI Evleri DG4-B Kat 2 Daire 3 Kadirli, Osmaniye, Turkey
Tel: +90 505 585 35 34, +90 328 717 77 77; Fax: +90 328 717 84 03
E-mail: [email protected]
Received: May 12, 2014 Accepted: June 09, 2014 Published: July 12, 2014
Citation: Cimen A, Ekmekci A, Uluganyan M, Cekirdekci EI, Selcukbiricik F, et al. (2014) Demonstration of Early Endothelial Dysfunction in Diabetics with Normal Exercise Electrocardiogram. Int J Cardiovasc Res 3:4. doi:10.4172/2324-8602.1000173

Abstract

TDemonstration of Early Endothelial Dysfunction in Diabetics with Normal Exercise Electrocardiogram

Endothelial dysfunction is considered to be an early marker for atherosclerosis. In the present study, we evaluated carotid artery intima-media thickness (IMT), and coronary flow reserve (CFR) by transthoracic echocardiography (TTE) in type II diabetes mellitus (DM) patients that have no ischeamic symptomson treadmill test.

Keywords: Endothelial dysfunction; Carotid artery intima media thickness,Coronary flow reserve; Echocardiography; Diabetes mellitus

Keywords

Endothelial dysfunction; Carotid artery intima media thickness; Coronary flow reserve; Echocardiography; Diabetes mellitus

Introduction

Endothelial dysfunction (ED) is one of the most important risk factors for atherosclerosis. Coronary angiography (CAG) is commonly used to detect coronary artery disease (CAD) by revealing coronary stenoses. However, CAG does not give sufficient information about coronary circulation physiology and endothelial function. Recently, to demonstrate endothelial function and micro vascular circulation, transthoracic echocardiography (TTE) and coronary flow reserve (CFR) have emerged as two important modalities [1]. The coronary vascular reserve (CVR) is the capacity provided by coronary flow to supply additional oxygen. CFR shows the CVR increment capacity according to the myocardial metabolic demand. One of the indicators of ED is no dilatation with rise in metabolic demand. Using this principle CFR could predict both epicardial and micro vascular coronary artery circulation confidentially [2].
The intima-media thickness (IMT), measured by carotid artery ultrasonography (USG), is one of the non-invasive methods that can evaluate early atherosclerotic changes. Increase in IMT is seen in asymptomatic atherosclerosis and is directly related with CAD [3]. The IMT measurement is one of the important indicators for detection of early phases of coronary atherosclerosis. The increase in carotid artery IMT is directly related to age, diabetes mellitus (DM), total cholesterol and smoking history [4]. There is also a close relation between carotid artery IMT and myocardial infarction (MI), aortic aneurysm and peripheral artery disease [5].
In this study, we evaluated carotid artery IMT and CFR measurements by TTE in type II DM patients that have no ischeamic symptoms on treadmill test.

Materials and Methods

All patient recruited, underwent an exercise test using the modified Bruce protocol. No patients had a clinical or electrocardiographic contraindication (such as left bundle branch block, paced rhythm, pre-excitation syndrome or atrial fibrillation) for exercise testing. The criterion for a positive test was ≥1 mm horizontal or convexial ST depression in at least 2 contiguous or extremity leads.
In this study, we enrolled 88 participants. Of these 51 were diabetic; in the diabetic group, 25 participants had a positive treadmill test for ischemia and 26 had a negative treadmill test. Thirty-seven participants were enrolled as a control group; they had no previous structural heart disease and undergone a treadmill test which was negative for ischemic changes.
Group I (Control Group): Participants with no structural heart disease and undergone a treadmill test with negative result of ischemic changes. Group II: Participants with DM but negative treadmill test; this group consist 16 men (62%), 10 women (38%) with mean age ± SD of 54 ± 2 years. Group III: Participants with DM and positive treadmill test; this group consisted of 15 men (60%), 10 women (40%) with mean age of 57 ± 2 years. All participants gave written permission prior to enrollment to the study. The study was approved by the ethics committee of Istanbul University, Istanbul Medical Faculty.
Echocardiography
Transthoracic echocardiographic examinations were performed on all participants using a GE Vivid 7 echocardiography machine (General Electric, Wisconsin, USA) using standardized methods. The measurements were done by 2-D and M-Mode echocardiography as described in the American Society of Echocardiography’s Guidelines and Standards Committee and the Chamber Quantification Writing Group recommendations. LV diastolic filling pattern was measured using pulsed wave doppler from the transmittal flow. The deceleration time (DT) was measured from the peak time of the E wave to where flow becomes zero (where the E wave cuts the time axis). The isovolumetric relaxation time (IVRT) was measured from an apical 4 chamber view using previously described methods [6].
Carotid intima-media measurement
The CMT was measured with a 10MHz linear probe of the same echocardiography machine. The carotid communis, bulbus, carotid interna and externa were examined. The CMT was measured from the distal carotid communis, 15-20 mm proximal to the carotid bulbus. The two bright lines at the arterial vessel wall were assumed to be the intima and media layers. For each case 3 measurements were taken from both the right and left carotid communis artery and the average of the 3 measurements were recorded for each right and left carotid artery. Measurements were not taken at regions that contained atherosclerotic plaque [3].
Coronary flow reserve measurement
The CFR measurement was performed with a 3 MHz probe with the same echocardiography machine. The left anterior descending (LAD) artery mid-distal flow was obtained at the left lateral decubitis position from the cutting point of the midclavicular line and 4th-5th intercostal space, at the left ventricular apical two chamber view with an 12-15 cm/sn color Doppler. Firstly, with a pulsed wave doppler, the coronary flow velocity (CFV) basal value [the peak diastolic velocity (PDV) flow] was measured. Participants were then given 0.56 mg/kg dipiridamole for 4 minutes. If heart rate increased < 10% of the basal value, another 0.28 mg/kg dipiridamole was infused. The CFR was measured using the hyperemic PDV flow / basal PDV flow formula [1,2] The participants were monitored and arterial tension was recorded during the infusion.
Statistical analysis
All statistical analysis was carried out by using SPSS version 16.0 for Windows (SPSS, Inc, Chicago, Illinois). A 2-tailed p<0.05 was considered significant with a 95% confidence interval. Categorical variables were analyzed by Pearson’s χ2 test and Fisher’s Exact Test. Differences between the groups were analyzed using one way ANNOVA Bonferroni adjustment. Correlation between parameters was done with simple linear correlation analysis.

Results

The basal demographic and hemo-biochemical parameters of control and diabetic groups are shown in Table 1. Thirty-seven control participants [of which 21 (56%) men] and 51 DM patients [of which 31 ( 60% ) men] were recruited to the study; the mean age of the diabetic patients was 55±9years and for the control group was 54±3years. Age, gender, smoking status, HDL, LDL hemoglobin (Hg) and creatinine (Cr) levels were comparable between the groups. Body mass index (BMI), total cholesterol and triglyceride levels were different between groups (p<0.001, p=0.007, p=0.003, respectively). The control and diabetic groups’ glucose and HgA1c level status are also shown in Table 1. The control group glucose level was 84.11 ± 11 mg/dl and diabetic group glucose level was 176 ± 94 mg/dl (p<0.001); the control group HgA1c level was 5.54 ± 0.21 and the diabetic group HgA1c level was 8.59 ± 1.87 (p<0.01). The control group carotid IMT was 0.57±0.16mm and the diabetic groups carotid IMT was 0.84 ± 0.25 mm (p<0.001). Even though the carotid IMT was not different between diabetic sub-groups, a significant difference was detected between diabetic and control groups (p<0.01) (Table 2 and 3).
Table 1: Basal demographic and laboratory parameters of control and diabetic groups.
Table 2: Comparison of carotid intima-media thickness between control and diabetic groups.
Table 3: Comparison of carotid intima-media thickness between control and diabetic subgroups.
The left ventricular M-mode measurements and diastolic function parameters of the groups were compared (Table 4). The LV wall thickness, LV mass and LV mass index were significantly higher in the diabetic group (p<0.001 for all). All LV diastolic parameters except IVRT were significantly different between groups (p<0.001 for DT, E/A, and Em/Am, p=0.16 for IVRT). The control group basal peak diastolic velocity was 29.9 ± 9.8 cm/sec and the diabetic group basal peak diastolic velocity was 33.5 ± 11.3 cm/sec (p=0.12). The control group hyperemic peak diastolic flow (HPDF) was 75.9±24.4cm/sec and the diabetic group HPDF was 59.3 ± 20.0 cm/sec. The control group CFR was 2.59 ± 0.57 and the diabetic group CFR was 1.81 ± 0.46. The HPDF velocity and the CFR were significantly different between groups (p=0.0007 and p<0.001 respectively) (Table 5).
Table 4: Comparing left ventricular echocardiographic parameters for control and diabetic groups.
Table 5: Comparison of coronary flow parameters between control and diabetic groups the left ventricular echocardiographic parameters.

Discussion

The relation between DM and CFR
Basal diastolic flow was similar between diabetic and control groups. Irrespective of the treadmill test, CFR of the control group was significantly higher than diabetic group (CFR: 2.59 ± 0.57 and 1.81 ± 0.46, p<0.001 respectively). CFR of group I was significantly higher than groups II and III. The CFR of group III was lowest but this was not significant (CFR; 2.59 ± 0.57, 1.68 ± 0.10, 1.94 ± 0.09, respectively). It has been shown that, CFR measured with TTE and invasive methods are similar.
Kranidis et al. studied LAD coronary flow reserve with transesophageal echocardiography in 32 DM patients and 27 control subjects [7]. The LV end-diastolic diameter, LV end-systolic diameter, interventricular septum, posterior wall thickness and basal LAD diastolic flow were similar. After dypiridamole infusion, the CFR of the diabetic group significantly lowered (CFR; 1.946 ± 0.743 vs 2.81 ± 0.345, p < 0,001) [7]. The dilatation of the micro vascular bed had detoriated. With an endothelial independent vasodilator infusion (papaverine, dypiridamole, adenosine) the maximal coronary flow in diabetic patients was impaired compared with non-diabetics [8,9]. CFR reduction may be seen without epicardial coronary artery stenosis and reflects microvasvcular disease. Nishino et al studied diabetic patients with retinopathy (a clinical indicator of microvasvcular disease) in whom CAG was normal. They found that CFR was reduced in diabetic patients but not in controls (CFR; 1.4 ± 0.4 ve 2.1 ± 0.5, p<0.01) [10].
Even in the absence of epicardial coronary artery stenosis, CFR reduction increases cardiovascular events [11]. Yokoyama et al investigated myocardial flow reserve in asymptomatic type II DM patients with myocardial perfusion sintigraphy. The basal myocardial flow reserve was similar between the groups but both hyperaemic myocardial flow and myocardial flow reserve were significantly higher in the control group than diabetic group [12].
Relation between CFR and Glucose
We found a negative correlation between CFR and glucose and HgA1c levels (r= -0.43, p<0.01; r = -0.56, p<0.01 respectively). Fujimoto et al studied healthy subjects and found CFR decreased from 4.4 ± 0.7to 3.8 ± 0.7 after oral glucose loading (p<0.001) [13]. This study indicated reflects that the acute oxidative stress after acute hyperglycemia leads to detoriation of endothelial dependent vasodilatation. Hyperglycemia plays a major role of endothelial dysfunction in diabetic patients. It can detoriate endothelial dependent vasodilation. Treatment of hyperglycemia can restore the microvascular arteriolar endothelial dependent vasodilation with subsequent rise in CFR. Miyazaki et al treated DM patients and glucose level decreased from 270 ± 106 mg/dl to 116 ± 39 mg/dl [14]. As a result they demonstrated a rise in CFR (CFR: 2.47 ± 0.55 vs 2.98 ± 0.56 p<0.001) [14].
Relation between DM and IMT
In this study we found that IMT was significantly increased in both DM groups compared with the control group (0.57 ± 0.16 mm versus 0.84 ± 0.25 mm, p<0.001). In both DM groups, the IMT was significantly higher than the control group. Although no significant difference of IMT was found between DM group II and III, group III IMT was higher than group II (0.79 ± 0.04 mm ve 0.90 ± 0.04 mm). Different studies have shown that IMT is increased in DM patients [15,16]. In The Chennai Urban Rural Epidemiology (CURE-22) trial, IMT in the control group was 0.69 ± 0.12 mm, in impaired glucose tolerance group was 0.75 ± 0.16 mm, in newly diagnosed DM group was 0.79 ± 0.19 mm and in previously diagnosed DM group was 0.87 ± 0.24 mm (p<0.001) [17]. Regresion analysis revealed a linear correlation between IMT and glucose tolerance [17].
The increment of carotid IMT is related to CAD and peripheral artey disease (PAD). The Atherosclerosis Risk in Communities (ARIC) study is an important study that highlighted the relation between CAD and IMT [18]. A total of 14054 participants (1500 DM patients) between 45-64years were followed for 10 years. Participants with an IMT >1 mm encountered significantly more new cardiovascular events than those with an IMT<1mm. The cardiovascular event incidence increment in women was 4 fold higher than in men [2,5]. Other studies have shown that MI and stroke risk increased when the IMT is greater than 1mm [19,20]. Falsom et al had showed a close relation between IMT and CV events [21]. The incidence of CV events in diabetic women was 15.2% if IMT < 1mm and 52.7% if IMT ≥ 1mm. In non-diabetic women, the CV events incidence was 3.4% if IMT < 1 mm and 10.1% if IMT ≥ 1 mm. In diabetic men CV events incidence was 24.4% if IMT < 1 mm and 48.4% if IMT ≥ 1 mm. In non-diabetic men CV events incidence was 10.6% in IMT<1 mm and 32.2% in IMT ≥ 1 mm. Bots et al have indicated that for a 0.63 mm increase in IMT, the MI risk increases 1.43 fold and stroke risk increases 1.4 fold [22]. In a meta-analysis performed in 4019 diabetic patients Brohall et al. demonstrated that IMT was 13% higher than the control group and in 10years this was related to a 40% increment of CV events risk [23]. The same study also showed that IMT of patients with impaired glucose tolerance was 0.04 mm higher compared with the control group.
Relation between IMT and Glucose
We have found a positive correlation between IMT and glucose/ HgA1c concentration (r = 0.35, p<0.01 and r = 0.43, p<0.01 respectively). Hyperglycemia can cause endothelial dysfunction with resultant increase in the IMT. In one study Sandler et al followed 3543 subjects over 2 years; of these 800 were diabetic [24]. The IMT progression rate in the non-diabetic group was 0.011mm/year and in the diabetic group was 0.018/year (p<0.03). They also found a positive correlation between IMT and HgA1c concentration (r = 0.08; p<0.0001).
Comparison of CFR and IMT
In this study we compared the carotid IMT and CFR. We found a significant negative correlation between carotid IMT and CFR (r = –0.33, p<0.01). Gullu et al. studied healthy subjects and found that carotid IMT was an independent predictor of CFR and found a negative correlation between carotid IMT and CFR (r= –0,41, p<0.01) [25]. Similarly, different studies have presented a negative correlation between carotids IMT and CFR [26,27].
Atherosclerosis follows a rapid course in diabetic patients with more frequent and serious cardiovascular outcomes compared with non-diabetics [6,29].Therefore, early diagnosis of atherosclerosis in diabetic patients, before CAD and MI occur, is important. The treadmill test is an easily accessible method but a negative result does not mean that atherosclerosis is absent. It is known that even in the absence of epicardial coronary stenosis, micro vascular disease decreases CFR and depresses LV function [10]. An indicator of endothelial dysfunction, CFR reduction, has been demonstrated in treadmill test negative diabetic patients [28]. In present study, CFR showed a non-significant reduction in the diabetic group, even those with a negative treadmill tests. Treadmill test positive diabetic patients, CFR was lower than treadmill test negative patients, but this failed to reach statistical significance, most likely due to the small number studied. CFR has a high negative predictive value. A normal CFR value indicates normal endothelial function and an abnormal value indicates micro and/or macro-vascular problems [30].
The study had some limitations. The main limitation of our study was the low number of participants. Also, we were only able to evaluate flow in the LAD with TTE and not the circumflex and right coronary arteries. Additionally, we have no follow up and CAG data for our patients.

Conclusion

In conclusion, in the present study we have demonstrated that, in diabetic patients, carotid IMT is increased and CFR decreased even in the absence of negative treadmill test. Atherosclerosis is started earlier in diabetic patients. All diabetic patients irrespective the status of the treadmill test deserve the same kind approach.

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