Objective: The association of resistant hypertension (RHTN) with renal haemodynamics is unclear. Our aim was to evaluate differences in haemodynamic characteristics of patients with RHTN compared with patients with controlled hypertension (HTN) at the level of the heart, kidney and aorta.
Methods: We studied 50 patients with RHTN confirmed by ambulatory blood pressure monitoring and 50 controlled hypertensive patients matched for age and sex. All participants underwent renal Doppler ultrasound to determine the renal resistive index (RRI), a complete echocardiographic study including measurements of diastolic function and evaluation of augmentation index.
Results: Hypertensive patients with RHTN compared with those without RHTN had a significantly decreased E/A ratio (by 0.12, P = 0.043), an increased E/e' ratio (by 3.1, P < 0.001), increased albumin-to-creatinine ratio levels (by 49 mg/g, P = 0.023) and a significantly higher RRI (by 0.078, P < 0.001) but similar augmentation index values (P = 0.79). Logistic regression revealed that presence of RHTN was the strongest predictor of an RRI more than 0.7 after controlling for other haemodynamic variables including blood pressure levels. Receiver-operator characteristic analysis revealed an area under the curve for prediction of RHTN by the RRI alone of 80.3% (95% confidence interval: 0.72-0.89, P < 0.001). An RRI cut-point of 0.648 has a sensitivity of 78% and a specificity of 72% for prediction of RHTN.
Conclusion: In a well treated hypertensive population, patients with RHTN show more pronounced renal and cardiac haemodynamic dysfunction compared with patients with controlled HTN. A greater RRI seems to be associated with RHTN and may help identify such patients.