The present study was a hospital based observational study conducted between June 2017 to October 2018 in the Department of Cardiology. One hundred and twenty consecutive patients presenting with symptoms suggestive of CAD with age >18 years and those willing to undergo conventional coronary angiography were included. Patients with cardiogenic shock, Chronic kidney disease (eGFR <30 mL/min), malignancy, hepatic dysfunction, pregnancy, and contraindications to angiography were excluded. Institutional ethical committee approved the study.

Informed consent has been taken from all the patients included in the study. Each patient underwent clinical examination, electrocardiography, 2D Echo and laboratory profile. All patients underwent coronary angiography and SS was calculated. The SS was calculated by a computer program consisting of sequential and interactive self-guided questions. The algorithm consists of 12 questions. After the assessment, based on the final score, patients were divided into low (0-22), intermediate (23-32) and high (≥33) SS [10]. The CHIs that includes CBP- Central Systolic Blood Pressure (CSBP), Central Diastolic Blood Pressure (CDBP), Central Pulse Pressure (CPP), PPA, PWV, AP, AIx corrected for heart rate at 75 bpm (AIx@HR75), Reflection Coefficient and Total peripheral resistance were measured. The CHIs obtained were then compared among the groups of low, intermediate and high SS to identify the parameters which correlate with severity of CAD.

Measurement of CHIs: PWA measurements were performed while subjects were in a quiet environment and after at least 10 min of rest in the supine position. PWA was assessed with AGEDIO B900 machine. The oscillometric wave obtained after applying brachial cuff with suprasystolic pressure resembles that of the blood pressure in the brachial artery proximal to the cuff with complete occlusion of the brachial artery under the cuff. A high fidelity pressure sensor was used which was connected to a conventional blood pressure cuff. The blood pressure is measured using an oscillometric method. The cuff pressure applied about 35 mmHg more than the measured systolic blood pressure and the pulse wave reflections are recorded by detecting the oscillations in the pressure [11].

The statistical analysis SPSS software 21.0 version was used for all statistical calculations. Continuous variables were given as mean±standard deviation and medians (range); categorical variables were described as percentages. Continuous variables were compared with ANOVA for normally distributed variables. Pearson’s correlation test (r) was used to assess the correlation between the two parameters. An optimal cut-off value to predict the presence of moderate to severe CAD (SS ≥23) by CHIs were determined using ROC analysis and AUC values. Statistical significance was defined as p<0.05.

One hundred twenty patients were recruited in the study. The mean age of presentation was 56.98±10.43 years. Most common age of presentation was between 51 and 60 years (N=54, 45%) followed by 41-50 years (N=28, 23.3%). The age range was between 21 to 72 years. [Table/Fig-1] shows the baseline characteristics of the whole study group.

Males were predominant than females with ratio of 4:1. Most of the patients were having dyslipidemia 70 (58.33%), followed by hypertension 58 (48.33%). Low SS was seen in 34 patients, intermediate in 36 patients and high SS in 50 patients [Table/Fig-1].

When the characteristics among the patients according to the SS were compared, high SS patients were found to be having diabetes (26 vs. 2 vs. 10), dyslipidemia (45 vs 17 vs 8), and increased BMI (27.16±2.55 vs. 22.65±2.12 vs. 21.80±1.73, p=0.001) compared to intermediate and low SS patients respectively [Table/Fig-2].

CHIs and their correlation with SS

There was no significant difference between males and females when compared the various CHIs measured by the oscillometric device [Table/Fig-3]. The same parameters were significant when compared among the groups according to SS [Table/Fig-4].

The correlation of the CHI variables with SS was assessed by the pearson correlation coefficient, and among the variables significant positive correlation with SS was seen with AIx (r=0.568, p=0.0001) and PWV (r=0.660, =0.0001) and negative correlation with PPA (r=-0.210, p=0.021) [Table/Fig-5].

On ROC curve analysis for detection of significant CAD, Augmentation Pressure cut-off value was 9.5 mm Hg (AUC 0.959, sensitivity 91.9%, specificity 88.2%), Augmentation Index cut-off value was 23.7 (AUC 0.90, sensitivity 88.4%, specificity 83.6%) and pulse wave velocity was 9.35 m/sec (AUC 0.955, sensitivity 81.4%, specificity 97.1%) [Table/Fig-6].

[Table/Fig-6]:

Receiver Operating Characteristic (ROC) curves of Augmentation Pressure, Augmentation Index and Pulse wave velocity, AUC-Area under curve.

The organs in the body are exposed to the aortic rather than brachial pressure, so assessment of the brachial blood pressure does not adequately risk stratify the patient compared to the central aortic pressure. It is more closely correlated with widely accepted surrogate measures of cardiovascular risk such as CIMT and LVM compared to the brachial pressure in cross-sectional studies. [8,9,11,12].

The present study have assessed the CHIs in patients with CAD and their correlation with SS. On analysis, males were predominant with most common age of presentation in between 51-60 years. Most common risk factor was dyslipidemia and hypertension. CAD severity by SS was high in 50 patients. When stratified according to SS, patients with high SS were having more risk factors compared to other groups. As the SS increased, there is increase in CSBP, CDBP, PP, Augmentation and decreased amplification with no change in TPR which is distinct compared to the previous studies.

The previous studies on CHIs were relatively underpowered regarding the significance of central pressure over the brachial values. CPP was found to be having independent predictor value on a meta analysis based on summary statistics rather than assessing the individual patient data (p=0.05) [8].

Comparison of the present study with previous studies is shown in [Table/Fig-7] [12,13].

Nakagomi A et al., compared various CHI’s by Oscillometric method and identified CPP, FPP and PPA values to be significantly correlated with presence and severity of CAD by Gensini Score (mean CPP- 62.2 vs. 51.7 in patients with CAD and without CAD respectively) [3].

Increase in aortic stiffness markers such as aortic PWV and Alx act as potent indicators of survival in ESRD patients and the presence of CAD [13]. Covic A et al., studied 46 patients with ESRD who underwent coronary angiography [14]. The AIx correlated with the atherosclerotic burden score in the coronary angiogram. ROC analysis demonstrated an optimal AIx of 17% (sensitivity 0.87 and specificity 0.7). PWV of aorta compared to the extremity arteries was a significant predictor of mortality in hemodialysis patients [15].

Bechlioulis A et al., studied CHIs with applanation tonometry in 393 patients with suspected stable CAD who underwent angiography [16]. Increased PWV was associated with the presence of CAD. Mean PWV in the study was 9.1 m/s. The results of the Rotterdam Study indicated that aortic PWV predicted the occurrence of CAD and stroke [6].

Tautu O et al., studied arterial stiffness by the oscillometric method in young MI patients and identified PWV (mean of 9.1±1.77 m/s) correlated with the severity of CAD (p=0.003, r²-0.27) [17]. In the study done by Covic A et al., patients with normal angiograms had significantly less arterial stiffness compared with the 35 subjects with evidence of obstructive coronary disease at angiography. PWV showed a cut-off value of 8.35 m/sec on ROC curve analysis (sensitivity=0.77; specificity=0.60) [14].

Sharma KH et al., studied the impact of CAD on AIx as measured by CBP as a case-control study in 505 Asian Indians (308 CAD vs. 277 Controls) and concluded that parameters such as CSBP and AIx are effective predictors of CAD in Asian Indians [18].

Chirinos JA et al., studied whether aortic pressure augmentation predicts adverse cardiovascular events in patients with established CAD [19]. In the study, it was determined that Augmentation Pressure (AP) was a significant predictor of death. For every 10 mm Hg increase in AP, there was an 18% increase in the risk of death.

In the present study, positive significant correlation was seen with AIx, PWV and negative correlation with PPA. Cut-off value of AIx and PWV to diagnose a patient with significant CAD on ROC curve analysis are 23.7 (AUC 0.90, sensitivity 88.4% and specificity 83.6%) and 9.35 m/sec (AUC 0.955, sensitivity 81.4%, specificity 97.1%) respectively.

As this was a small study further large scale studies are warranted to define the optimal values of CHIs for identifying patients with severe CAD in Indian population. Large number of patients to be assessed and followed-up with reference to change in the CHIs on management and symptom improvement.

Central Hemodynamic Indices (CHIs) assessed noninvasively had good correlation with severity of coronary lesion and were predictive of significant CAD. Their assessment can help in risk stratification of the CAD patients. Guidelines emphasising their assessment in evaluation of CAD patients is of high need and expected in the near future.