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Increase in sympathetic nerve activity from mitral regurgitation may be attenuated by mitral valve repair
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In patients with chronic HF, secondary mitral regurgitation appears to be correlated with increased sympathetic nerve activity, but transcatheter mitral valve repair may improve outcomes, according to new findings.
In the study, researchers prospectively evaluated patients with chronic HF related to left ventricular systolic dysfunction (LV ejection fraction < 40%)who were consecutively enrolled between January 2014 and July 2015. Thirty patients (mean age, 79.2 years; 73% men) had symptomatic moderate to severe mitral regurgitation (grade 2 or higher) and 20 controls matched for age, sex, BMI, functional status and cardiac comorbidities (mean age, 71.3 years; 85% men) had no symptoms of significant mitral regurgitation.
Patients also were subjected to clinical examinations, a 6-minute walk test, routine laboratory assessments and microneurography, which assessed muscle sympathetic nerve activity. The researchers assessed N-terminal pro-B-type natriuretic peptide and noradrenaline concentrations from blood samples.
Valve repair
Sixteen patients in the symptomatic group underwent successful transcatheter mitral valve repair with the MitraClip system (Abbott Vascular). Six-month follow-up assessments included clinical examination, routine labwork, transthoracic echocardiography, a 6-minute walk test and repeated microneurography testing.
The researchers found that, in the overall cohort, LVEF as assessed by echocardiography was 37.6%, with patients in the symptomatic group demonstrating better LV systolic function (43%) vs. those in the control group (29%; standardized difference [d] = 0.64).
Symptomatic mitral regurgitation alone was linked to elevated muscle sympathetic nerve activity (symptomatic group, 106 ± 59 burst per minute; control group, 74 ± 48.1 burst per minute; d = 0.58), diminished sympathetic baroreflex gain (symptomatic group, 10 ± 7 burst/mm Hg; control group, 5 ± 5 burst/mm Hg; d = 0.61) and increased heart rate (symptomatic group, 90 ± 27 bpm; control group, 78 ± 12 bpm; d = 0.58). Patients with symptomatic mitral regurgitation had an increased muscle sympathetic nerve activity burst incidence (119 ± 63 burst/100 beats), but this was not significantly different from that of the control group (93 ± 58 burst/100 beats; d = 0.48).
Although the overall cohort showed elevated serum levels of NT-proBNP (88,323 ± 13,907 pg/mL) and noradrenaline (883 ± 493 ng/L), there were no differences between groups in either measure.
At 6 months, follow-up information was available for 10 patients with symptomatic mitral regurgitation had undergone transcatheter mitral valve repair and nine from that group who had not.
Improvements shown
During follow-up, patients with symptomatic mitral regurgitation who underwent transcatheter mitral valve repair showed improvements in functional NYHA class (2.8 ± 0.4 vs. 1.6 ± 0.5; d = 0.61), as well as in 6-minute walking distance (204 ± 33 m vs. 288 ± 46 m; d = 0.64). In that group, NT-proBNP levels were reduced from 5,251 pg/mL to 3,710 pg/mL (d = 0.58), but noradrenaline levels were unchanged, according to the researchers.
Additionally, patients with sympathetic mitral regurgitation who underwent transcatheter mitral valve repair demonstrated reductions in muscle sympathetic nerve activity burst-frequency (130 ± 78 bursts/min vs. 74 ± 21 bursts/min; d = 0.58), baroreflex gain (7 ± 4 bursts/mm Hg vs. 4 ± 1 bursts/mm Hg; d = 0.61) and burst-incidence (143 ± 88 bursts/100 beats, 113 ± 34 bursts/100 beats; d = 0.48), the researchers wrote. No changes in muscle sympathetic nerve activity were seen in patients with untreated symptomatic mitral regurgitation (d < 0.5).
“Patients with secondary mitral regurgitation had higher sympathetic activity levels when compared to patients with [chronic HF] but without mitral regurgitation,” the researchers wrote. “Determination of sympathetic nerve activity might contribute to a better understanding of the effects of interventional treatment of symptomatic mitral regurgitation on patients’ functional outcome and survival.” – by Jennifer Byrne
Disclosure: The researchers report no relevant financial disclosures.
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