To the Editor:
I have read through the article of Denfeld and colleagues1 with great interest, showing the association between sympathetic nerve dysfunction assessed by several biomarkers and impaired quality of life (QOL) assessed by the Kansas City Cardiomyopathy Questionnaire Clinical Summary score after left ventricular assist device (LVAD) implantation. Given the significant improvement in survival after LVAD implantation thus far, QOL, the end point used in their study, would be the next target to be addressed. Their findings may let us focus on the sympathetic nerve system as a therapeutic target to improve patients' QOL during LVAD support.
However, their findings may raise another concern to be clarified: why was sympathetic nerve dysfunction associated with poor QOL. Poor QOL may result from various clinical abnormalities, including reduced exercise capacity, more frequent readmissions due to multiple comorbidities, or even social issues. The impact of sympathetic nerve dysfunction on these clinical abnormalities may explain the detailed mechanism of their findings.
Our team previously demonstrated that reduced sympathetic nerve activity, demonstrated by iodine-123 meta-iodobenzylguanidine scintigraphy, was associated with less reverse remodeling of the left ventricle after LVAD implantation, probably due to impaired cardiac reserve.2 Patients with less remodeled left ventricle may have impaired exercise capacity and reduced QOL, and such population may be "clinical nonresponders", as defined by Denfeld et al. defined in their study using the Kansas City Cardiomyopathy Questionnaire.
Further studies addressing the detailed relationship between the sympathetic nerve dysfunction and reduced QOL, including exercise tests and echocardiographic assessments, are warranted to strengthen their findings and construct a novel strategy to treat the sympathetic nerve system. Implications of aggressive treatment for sympathetic nerve activity on patients' QOL after LVAD implantation is also a next concern.
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