Hypomagnesemia after heart transplantation or left ventricular assist device implant for end-stage heart failure

Background: Patients with advanced heart failure undergoing heart transplant (HTx) or left ventricular assist device (LVAD) implant are at high risk of magnesium deficiency, that may favor development of diabetes. We aimed to comparatively assess prevalence and correlates of hypomagnesemia during cardiac rehabilitation between 51 HTx and 46 LVAD recipients. Methods and Results: We measured serum magnesium and correlated it to clinical and laboratory findings upon admission (T₁) and at discharge (T2) from cardiac rehabilitation. Among LVAD, magnesium levels increased from admission to discharge. Among HTx, magnesium concentrations were below normal in 33% and 47% at T₁ and T₂, respectively, and decreased from admission to discharge. HTx on tacrolimus showed greater decreases in magnesium and increases in glucose levels than those on cyclosporine. Magnesium levels were inversely associated with >15 mg/dL increased glucose concentrations between T₂ and T₁ (HR 0.373, 95% CI 0.154-0.903, P =.029) after adjustment for pre-existing diabetes, insulin resistance markers, calcineurin inhibitors (cyclosporine/tacrolimus), prednisone doses, and magnesium supplementation. Conclusion: Hypomagnesemia is rare in LVAD recipients, but common within 1 month from HTx, worsens during rehabilitation, despite immunosuppression tapering and magnesium supplements, and is independently associated to increasing glucose levels. Studies evaluating whether correcting hypomagnesemia improves outcome are warranted.