Dec 12, 2013
High blood pressure or Hypertension is a leading cause of heart attack and stroke in the US and worldwide. The World Health Organization has identified hypertension as the most important risk factor for all cause mortality accounting for about 12% of the attributable hazard for death in the world. Currently, one third of American adults suffer from hypertension with that number expected to increase to one in two over the coming decade. Beyond the cardiovascular risks, end organ injury to the heart and kidneys can also result in systolic heart failure, chronic kidney disease and even end stage renal disease requiring dialysis.
It is estimated that up to 50% of those suffering hypertension have inadequate control. The causes of poorly controlled hypertension range from lack of access to healthcare, to patient noncompliance or physician noncompliance.
Other causes of poorly controlled hypertension are related to correctable secondary issues including:
Pheochromocytoma, Hyperaldosteronism, Cushing Syndrome, Hyperparathyroid, Hyperthyroid, Coarctation, Aortic Coarctation, Sleep apnea, NSAIDS, OCP.
Finally, an important and sometimes overlooked cause of hypertension is “white coat phenomena” in which patients experience high blood pressures while in the providers office only. Typically, the patient can be evaluated with an ambulatory monitor for 24 hours which will verify that the blood pressure is normalized outside of the office.
As secondary causes of hypertension are evaluated and ruled out, most patients are placed on a heart healthy low sodium diet and optimized on a medication regimen if necessary. Despite these efforts a subgroup of hypertensive patients, from 5-20%, will continue to have suboptimal control of their blood pressure while maintained on 3 antihypertensive agents of different classes at maximal tolerable doses. Studies suggest that this group of patients carries a long term higher risk of cardiovascular complications.
A growing body of recent research suggests that selective renal artery denervation using radiofrequency ablation causes reductions in blood pressure which may over time translate to fewer cardiovascular complications in affected patients. Renal artery denervation is currently not FDA approved for use in the United States. Ongoing investigational trials (See ReduceHTN, Boston Scientific) hope to confirm earlier studies suggesting that the procedure is safe with a low rate of complication and the earlier data showing that reductions in blood pressure are consistent, reproducible and sustained.
Current renal denervation systems involve the catheterization performed from the groin region. Angiographic images are obtained of the renal arteries. A wire is then inserted into the renal artery and an ablative catheter threaded over that wire and carefully positioned with XRAY guidance in the blood vessel. The procedure is identical to commonly performed angioplasty.
The catheter then delivers a safe degree of heat through electrodes positioned on the balloon at carefully selected locations. The heat is able to destroy nerves that course along the outside and within the mid wall of the blood vessel-without causing any damage to the artery wall. The heat is delivered over 2 minutes. Because heat is applied, the patient is given intravenous sedation to minimize discomfort during the procedure.
Following the procedure, the patient is monitored and able to go home the following day. The effect is not immediate. Over time however, the blood pressure begins to lower. Early studies show a reduction of 27/17 over 12 months and this reduction appears to be sustained in patients followed out to 3 years.
The important implication of this study is that in patients most severely affected by hypertension in which few options were previously available, an option now exists for reducing blood pressure. We know that reducing the blood pressure 20/10 can reduce that risk of heart attack and stroke by 50%.
In summary, renal artery denervation holds significant promise for reducing morbidity in drug resistant hypertensive patients. Further research is needed to determine in which patients the intervention works best in.