To the Editor:
Refractory or resistant hypertension (RHTN) is believed to affect 5% to 30% of the general population.1 The etiology of RHTN is almost always multifactorial. However, there is a small subset of patients who experience RHTN of neurogenic causes (RHTN-N). Some of these “hard to treat” patients with RHTN-N are candidates for a specialized surgical intervention designed to normalize their blood pressure. While performing microvascular decompression (MVD) for trigeminal neuralgia and hemifacial spasm, Jannetta and colleagues2 discovered a relationship between arterial compression of the brainstem, in particular the rostral ventro-lateral medulla (RVLM) and its impact on the regulation of sympathetic and cardiovascular activities. These initial findings have been validated by imaging, animal, post-mortem, and case studies. Specifically, the presence of arterial compression on the retro-olivary sulcus of the RVLM is responsible for the elevation of BP and sympathetic tone.3
Although a range of studies have been completed to examine the underlying causes of RHTN-N and the appropriateness of MVD, significant gaps remain in understanding: (1) which patients are most likely to benefit from MVD, (2) the efficacy of treatment in the population, (3) long-term outcomes, and (4) the cost-effectiveness of MVD as a treatment approach. We completed a comprehensive review of the literature related to MVD as a treatment approach for RHTN-N and identified 8 studies including 107 participants who reported outcomes following MVD. The primary findings of the review were that although MVD is used sparingly in patients with RHTN-N, the evidence suggests that BP can be normalized after MVD in some hard to treat patients with RHTN-N. More specifically, a rebound effect (ie, a reversal effect to elevated BP) was present in most studies during the follow-up period. In summary, MVD for treatment of EHTN offers short-term normalization of blood pressure and lowering/reduction of antihypertensive medications, MSNA, plasma, and urine norepinephrine.
These findings are important because treatment recommendations from the American Heart Association (AHA) call for both pharmacologic and nonpharmacologic treatment approaches.4 In that regard, there are a small subset of patients with RHTN-N who could potentially benefit from surgical interventions to normalize their BP. However, the long-term impact of the surgical procedure remains debatable. Despite questionable long-term outcomes, the observed positive short-term outcomes indicate potential for future interventions to improve BP in this population. For example, studies that reported extended follow-up periods (>1 year) also noted a rebound effect. However, this rebound effect has not yet been investigated in significant detail and only speculation has emerged as to why the phenomenon frequently occurs.
The Scientific Statement for the AHA “Resistant Hypertension: Diagnosis, Evaluation and Treatment” notes that experimental assessment of this population is complicated by coexisting high cardiovascular risk, which restricts the type and duration of experimental treatments.4 We understand that studying this patient population has not been and will not be easy going forward. To date, there have been no blinded randomized controlled trials to study MVD and it is unclear whether this study design is appropriate for this patient population. In addition, studying this population will likely be complicated by subgroups of patients with varying underlying neurogenic etiologies. Regardless, future studies are needed to examine the impact of MVD on the short- and long-term outcomes of hard to treat patients with RHTN-N.