Captopril test and renal duplex scanning for the primary screening of renovascular disease

Contemporary approach to diagnosis and evaluation of renovascular hypertension

Recommendations regarding the clinical protocols for radionuclides of choice and diagnostic criteria for renovascular hypertension have been established by the consensus report on captopril renography. A review of the existing data indicates that postcaptopril renography alone is a safe and effective means of noninvasively screening hypertensive patients. A normal radionuclide study after captopril suggests with a reasonable degree of certainty that potentially reversible renovascular hypertension is unlikely. A positive study in an appropriately screened hypertensive patient with preserved renal function suggests renovascular disease is likely with a sensitivity and specificity in excess of 90%. In the comparative studies of Elliott and Miralles and colleagues, captopril renography was a more sensitive and specific screening test than the captopril plasma renin activity test. Although there may be confounding variables, such as renal dysfunction, medications, and types of stenosis, a positive captopril renogram may suggest a cure or improvement in blood pressure control with successful intervention such as PTRA or revascularization. Whether captopril renography can predict stabilization of individual kidney function is speculative and deserving of further study.

Hypertension

The current JNC-VI criteria for diagnosis and classification of hypertension are discussed. The laboratory evaluation of both essential and secondary hypertension is examined, and recommendations are made in this regard. Finally, the complications and treatment of essential hypertension and the causes and management of resistant hypertension are discussed.

Evaluation of duplex ultrasound and captopril renography for detection of renovascular hypertension

BACKGROUND

Renovascular hypertension is the most common form of curable secondary hypertension and, if untreated, may lead to end-stage kidney disease. Given that renal function and hypertension may improve after renal angioplasty, it is pertinent to identify patients with renal artery stenosis. The aim of the present study was to evaluate both duplex ultrasound and captopril renography for detection of renal artery stenosis among hypertensive patients.

METHODS

To avoid selection bias, all patients referred to our center for evaluation of renovascular hypertension were asked to participate in the study. Patients were examined by intra-renal duplex ultrasound (N = 121), measuring pulsatility index and acceleration of the blood flow during early systole. In 98 patients, 99mTc-DTPA captopril renography was performed in conjunction with duplex ultrasound. Renal angiography was performed in all patients regardless of the results of the noninvasive tests.

RESULTS

The prevalence of renal artery stenosis was 19%. In the 98 patients examined by both duplex ultrasound and captopril renography, sensitivity and positive predictive values for detection of a renal artery stenosis of 50% degree or more were 84 and 76%, respectively, for duplex ultrasound, whereas captopril renography was associated with a sensitivity and positive predictive value of 68% for both (P = NS). Specificity and negative predictive values were 94 and 96%, respectively, for duplex ultrasound, whereas the corresponding values for captopril renography were 92% for both (P = NS). Specificity and negative predictive values were 94 and 96%, respectively, for duplex ultrasound, whereas the corresponding values for captopril renography were 92% for both (P = NS).

CONCLUSIONS

Both duplex ultrasound and captopril renography are associated with high specificity and negative predictive values for detection of renal artery stenosis. Sensitivity and positive predictive values are at least as good for duplex ultrasound compared with captopril renography. Given that duplex ultrasound is easier to perform and more cost effective, we propose that it should be the method of first choice when screening for renal artery stenosis in a hypertensive population.

Renovascular hypertension

Approximately 5% of all hypertensive patients have renovascular hypertension, although its true incidence is unknown. The pathophysiology of renovascular hypertension has been linked to other intrarenal systems, the lipoxygenase pathway, and renin angiotensin. Many advances have been made in this field, but emphasis is now being placed on using less invasive or non-invasive tests to identify functionally significant lesions with a high degree of accuracy. The treatment modalities have shifted from aggressive surgical revascularization to less invasive management. The use of arterial stents has simplified the management of patients with renovascular hypertension, but long-term results are not yet available.

Endovascular stents for renal artery revascularization

Revascularization cures or attenuates the clinical manifestations of renal artery stenosis (hypertension, ischemic nephropathy, pulmonary edema, angina, and congestive heart failure). Traditional approaches have been sub-optimal due to low rates of success and long-term patency after angioplasty, and to relatively high rates of perioperative morbidity and mortality. Endovascular stent placement is an alternative interventional method for renal artery revascularization. Technical success rates are excellent, and the impact on clinical outcomes (blood pressure, renal function, and cardiac complications) is promising.