Background: Despite advances in cardiovascular medicine, acute coronary syndrome (ACS) is still a major cause of morbidity and mortality worldwide. Synergy between percutaneous coronary intervention with TAXUS™ and Cardiac Surgery (SYNTAX) score is used to determine the extent and complexity of coronary artery disease (CAD). Renal resistive index (RRI), a renal Doppler ultrasound parameter, is used to detect renal haemodynamics. Although some risk factors for CAD, including hypertension and diabetes mellitus, were demonstrated to have an association with RRI; a direct relationship between the presence, extent, and complexity of CAD and RRI has not been investigated yet.

Aim: In this study, we evaluated the relationship between RRI and SYNTAX score in patients with ACS.

Methods: This cross-sectional study enrolled 235 patients who were diagnosed with ACS and underwent coronary angiography at our tertiary clinic between February 2016 and August 2016. Regarding clinical presentation, 112 patients were diagnosed with non-ST-segment elevation ACS (NSTE-ACS) and 123 patients were diagnosed with ST-segment elevation ACS (STE-ACS). The patients’ demographic, clinical, laboratory, echocardiographic data, SYNTAX scores and measurements of renal Doppler ultrasound parameters, including RRI, renal pulsatility index (RPI) and acceleration time (AT) were recorded.

Results: Among 235 patients, 112 (47.7%) were diagnosed with NSTE-ACS and 123 (52.3%) were diagnosed with STE-ACS. Mean SYNTAX score and RRI of patients with NSTE-ACS and STE-ACS were 15.4 and 0.69, 21.1 and 0.67, respectively. The SYNTAX score was associated with gender, height, plasma uric acid level, left atrial diameter, left ventricular (LV) end-systolic and end-diastolic diameter, RPI, and RRI in patients with NSTE-ACS, as well as with low-density lipoprotein-cholesterol, total cholesterol, ejection fraction, and LV end-systolic diameter in patients with STE-ACS (p < 0.05 for each variable). RRI was significantly associated with age, haemoglobin level, left atrial diameter, SYNTAX score, AT, and RPI in patients with NSTE-ACS, as well as with weight, body mass index, interventricular septum thickness at diastole, LV posterior wall thickness at diastole, LV ejection fraction, and RRI in patients with STE-ACS. Multivariate logistic regression analysis demonstrated that LV end-systolic diameter (β = 0.385, 95% CI 1.065–2.029, p = 0.019), RRI (β = 32.230, 95% CI 5343.15–2.E+24, p = 0.008), and RPI (β = –7.439, 95% CI 0.000–0.231, p = 0.015) were independent predictors of moderate to high SYNTAX score in patients with NSTE-ACS.

Conclusions: Non-invasively detected RRI is closely associated with the extent and complexity of CAD in patients with NSTE-ACS. However, there is a need for randomised, controlled studies involving wider populations.