Brachial–brachial index of systolic blood pressure in the patients under anti-hypertensive therapy

Abstract

Inter-arm BP difference (IAD) has been demonstrated not only as a useful marker for subclavian artery stenosis [1,2], but also as a predicator for increased cardiovascular morbidity and mortality [1,3]. However, the detection rate of systolic IAD (sIAD) significantly varies with the SBP level in hypertensive patients under antihypertensive therapy [4]. Thus this phenomenon may induce confusion and decrease the clinical values of sIAD for diagnosing subclavian or brachial artery stenosis and predicting cardiovascular events. Therefore, it is necessary to create a new parameter, which could more correctly evaluate the difference between two arms at different BP levels. We hypothesize that systolic brachial–brachial index (sBBI), the ratio of right to left arm SBP, may be a more consistent index than sIAD. This study was to test our hypothesis and primarily evaluate the clinical value of sBBI. From May to November of 2012, 414 (200 males and 214 females, 61.3 ± 13.3 y) consecutively adult hypertensive patients admitted to ourhospitalwardwere enrolled. The inclusion criteriawere the baseline SBP/DBP (taken at admission) of at least 140/90 mmHg on the higher value of two arms. The exclusion criteria were arrhythmia, acute myocardial infarction, aortic coarctation, congenital heart disease, heart failure, hemiplegia, pulseless disease and the history of transradial coronary intervention. All patients were right handedness. The BP of two arms was simultaneously measured using two validated automatic BP measurement devices (Omron, HEM-7112) for 3 times with a 2-min interval. The absolute SBP difference between right (SBPr) and left (SBPl) arms was calculated as SBPr-l. The SBPl-r of 10 mm Hg or more was diagnosed as sIAD [1,5–7]. sBBI was calculated on the formula: SBBI = SBPr / SBPl. The patients with consistent sIAD (diagnosed for 3 determinations) received color Doppler flow imaging examination for bilateral subclavian, axillary and brachial artery [8,9]. Continuous variables were expressed as mean ± SD. The t-test, variance (ANOVA) test and the omnibus test were used for the statistical analysis. The chi-square test was used to compare the IAD detection rate. The inter-measurement agreement was evaluated by Bland–Altman plots [10]. The inter-measurement sIAD or sBBI differences between two measurements (firstminus second, secondminus third, and thirdminus first)were calculated.With thismethod, inter-measurement differences were plotted against their means and the 95% limits of agreement (LoA) were determined (95% LoA = mean inter-measurement difference ± 1.96 standard deviation). In order to compare the inter-measurement agreement, the variability of bias, SD of bias, lower limit and upper limit from 3 Bland–Altman plots on sIAD and sBBI were calculated separately on the formula: variability = SD / Mean. Meanwhile, the plots of outside of 95% and their percentages for each pair of measurements on sIAD and sBBI were calculated separately. P b 0.05 was considered statistically significant. The SBP levels of right armwere higher (about 4 mmHg) than those of left arm in the 3 stages. As SBP levels gradually decreased, SBPr-l gradually decreased, but the sBBIs were very similar. In this study, the abnormal sBBI limit was b0.95 or N1.10 based on the 1242 SBP values from 414 patients (normal limits = 1.023 ± 1.96 × 0.039). On these criteria, the detection rates of abnormal sBBI in three stages decreased from the first to the third as sIAD did, but the decreased extent was significantly less than that of sIAD (5:1 vs 2:1) (Table 1). The Bland–Altman plots on sIAD and sBBI among three measurements are showed in Fig. 1. The Bland–Altman plots on sIAD has rhombus-like left side and discrete right side, while the pictures of Bland–Altman plots on sBBI are like a core (Fig. 1). Meanwhile, the variability on the 4 parameters for sBBI was lower than their relative parameter on sIAD. Furthermore, point percentages located outside the 95% LoA between first and second, the first and third, and the second and third were lower on sBBI than on sIAD (4.59%, 3.87% and 3.38% vs 5.31%, 4.35% and 4.10%, respectively). In this study, ultrasonic examination was performed in 8 cases with consistent sIAD diagnosis [4]. One case with sBBI of 0.88, which