- A new meta-analysis of existing studies investigating a unique form of blood pressure control reports encouraging results.
- It describes a procedure that “mutes” overactive kidney nerves, a symptom often found in middle-aged people with hypertension.
- The procedure lowered the blood pressure of participants significantly, by an average of 8.5 millimeters of mercury (mmHG).
- This benefit was confirmed by follow-ups 2 months later, as well as 3 years later.
Hypertension, or high blood pressure, is one of the major global causes of death. It can lead to strokes, as well as heart, brain, and kidney disease. It is often referred to as the “silent killer,” as an estimated 46% of people who have hypertension do not know they have it.
Healthy lifestyle and diet changes can help manage the condition, and may be aided by numerous hypertension drugs that are sometimes prescribed in combination. For many people, this is sufficient. For some, however, blood pressure remains persistently high.
A new meta-analysis finds that using therapeutic ultrasound to calm kidney-nerve hyperactivity significantly lowered blood pressure among the 506 people with hypertension in three randomized clinical trials.
It is not entirely clear what causes hypertension, though experts suspect it may be a combination of genetic and lifestyle factors, as well as aging and other mechanisms.
Hypertension in middle age is frequently associated with overactive nerves in the kidneys, which may promote high blood pressure in several ways. It may trigger water and salt retention, and release hormones that increase blood pressure.
While there are various types of drugs that treat hypertension, none specifically target this renal overactivity. The “renal denervation” ultrasound technique explored in the new study, which calms overactive nerves in the kidneys, therefore offers physicians an additional tool with which to help patients remain healthy.
The study was conducted by researchers from Columbia University, New York City, and Université de Paris, France. It appears in JAMA Cardiology.
How blood pressure is measured
Blood pressure is measured in millimeters of mercury, or mmHG. This is because the first accurate blood pressure gauges relied on mercury, as do some modern devices.
Blood pressure is reported as two values, often shown one above the other, or one to the left of the other. The first value is systolic blood pressure, the pressure the heart exerts when it is pumping blood. The second, diastolic, value indicates the pressure in arteries between heartbeats.
The American Heart Association considers a systolic blood pressure of less than 120 mmHG over a diastolic pressure of less than 80 mmHG to be healthy. Stage 1 hypertension occurs with a reading of 130-139/ 80-89 mmHG. Higher readings signify stage 2 hypertension.
Overall, the new study found that renal denervation lowered participants’ blood pressure significantly, by 5 to 10 mmHG, with an average reduction of 8.5 mmHG.
Renal denervation
The renal denervation device discussed in the study involves a thin catheter inserted into a leg or wrist vein and threaded into the kidney. During the procedure, nerves in the kidneys are treated with ultra-high-frequency sound waves that produce tiny amounts of scar tissue to inhibit nerve activity. This process is called “ablation.”
“We anticipate it being an outpatient procedure similar to a cardiac catheterization procedure,” said lead author Dr. Ajay J. Kirtaine.
“The ablation portion for ultrasound-renal denervation is less than 1 minute, and the overall procedure is less than an hour, with conscious sedation/ local anesthesia,” he explained.
In the studies, one group of participants received the ultrasound denervation, while another group, the control group, received a sham procedure with no therapeutic value.
Twice as many individuals in the study arm that received the treatment achieved their blood pressure goals of 135/85. This result was consistent across the three studies with a racially diverse population, suggesting the procedure’s value is likely to be widespread.
The studies followed participants for 2 months after the procedure, and found that the improvement in blood pressure lasted at least that long.
Dr. Kirtaine said the effect of the procedure “appears to be durable with follow-up out to 3 years.”
Not for everyone, at least not yet
The device is experimental so far, having not received approval for use in the United States.
The authors of the study envision its use in patients whose blood pressure remains uncontrolled despite lifestyle modification and medication.
Cardiologist Dr. Jayne Morgan, who was not involved in the study, agreed, considering the process as potentially a secondary treatment, rather than a first-choice therapy.
“However, with continued trials and information/ data, I foresee that this could certainly be reversed in the future,” she added.
The procedure, added Dr. Morgan, may be especially helpful for minority populations with high rates of hypertension and heart disease, particularly Black individuals.
“This could provide a more permanent option for blood pressure control in the future, and is a great reason why [Black participants] should be recruited,” she said.
In the meta-analysis, 17% of participants were African American.
Dr. Devin Kehl, not involved in the research, cautioned that although the procedure has an excellent long-term safety profile, and is likely safe, “the trials have been pretty restrictive in their inclusion and exclusion criteria.”
“So, for example, most patients in the study didn’t have a lot of comorbidities,” he noted. “[The procedure] is associated with a low procedural risk, but it’s not a zero procedural risk.”
Overall, said Dr. Kehl, “it [the analysis] makes a pretty convincing case that ultrasound denervation belongs in the toolkit for the treatment of hypertension.”
Dr. Kehl concluded:
“Down the road, if a patient would consider this, it’s important to discuss with their doctor if the results can really be extrapolated to them. And we also will need more trials to understand to what degree this treatment effect holds in patients with other comorbidities.”
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