Renal arteries denervation with second generation systems: a remedy for resistant hypertension?

Figure 1. The kidney plays a key role in the regulation of cardiovascular function and in pressure homeostasis. Two main functions of the kidney are involved in cardiovascular control: the production and release of renin with consequent production of angiotensin II, a powerful vasoconstrictor agent, and the urinary excretion of Na which affects the fluid balance. Both of these effects are influenced by adrenergic nerve factors that play a key role in controlling renin release and saline balance through both direct and indirect mechanisms. In particular, the sympathetic nervous system has a key role in the regulation of perfusion and renal function through afferent and efferent fibres that reach the kidneys from the aorta with fibres located in the adventitia of the renal arteries.

Figure 2. Renal norepinephrine production is on average two to three times higher in patients with essential hypertension or secondary to obesity. This observation highlights the role of the sympathetic nervous system in regulating pressure and its activity increases early in hypertensive patients.

Figure 3. The comparison of the six-month blood pressure data of HTN-3 with those of the HTN-1 and HTN-2 studies is truly surprising. The evident effect of renal denervation on blood pressure values obtained in the HTN1 and HTN-2 studies could be linked to the phenomenon of ‘regression from the average’: typical bias of registers and observational studies, with very high standard deviation. Having ‘overestimated’ the effectiveness of the procedure in previous studies may have led to an error in the calculation of the sample size (calculation of power) of patients to be recruited in HTN-3.

Figure 4. Average changes in systolic blood pressure compared to baseline during 24-h outpatient recording and assessment of blood pressure values in three outpatient randomized denervation studies of renal arteries using second generation devices compared to groups in which the procedure was simulated (‘Sham’ group): all trials show a significant reduction in the mean 24-h pressure of the outpatient pressure and the systolic pressure in the renal denervation group compared with the follow-up control group.