Magnesium deficiency highlighted in Medscape Review
Since we emphasize the importance for afibbers to be sure they first optimize intracellular magnesium levels, it's encouraging to see recognition and emphasis on the importance of magnesium as it relates to overall health and arrhythmia in this recent Medscape Review
titled The Top 10 Clinical Trends of 2017. Included is a reference to magnesium deficiency as it relates to arrhythmia.
Clip: Trend 2: Magnesium Deficiency
Speculation on the death of a beloved celebrity resulted in the top clinical trend for early 2017. Carrie Fisher—an outspoken mental health advocate, author and actress died a few days after becoming unresponsive while on an airplane. Although nothing is certain, Dr. George Lundberg
Suggested the possibility that chronic magnesium deficiency may have been the cause of her untimely death. He described how low magnesium levels can trigger various cardiac rhythm abnormalities including fatal ones.
Dr. Lundberg explained that regardless of whether magnesium deficiency ultimately contributed to Fisher’s death, it is a serious and commonly-overlooked medical condition that deserves more consideration. Hopefully, the fact that magnesium deficiency is one of the top searches in 2017 is a sign that clinicians are doing just that. (end quote).
The cardiovascular effects of magnesium deficiency include effects on electrical activity, myocardial contractility, potentiation of digitalis effects, and vascular tone. Epidemiologic studies also show an association between magnesium deficiency and coronary artery disease (CAD).
Hypomagnesemia is now recognized to cause cardiac arrhythmia. [40, 41] Changes in electrocardiogram findings include prolongation of conduction and slight ST depression, although these changes are nonspecific. Patients with magnesium deficiency are particularly susceptible to digoxin-related arrhythmia. Intracellular magnesium deficiency and digoxin excess act together to impair Na+/K+ -ATPase. The resulting decrease in intracellular potassium disturbs the resting membrane potential and repolarization phase of the myocardial cells, enhancing the inhibitory effect of digoxin. Intravenous magnesium supplementation may be a helpful adjunct when attempting rate control for atrial fibrillation with digoxin. 
Non–digitalis-associated arrhythmias are myriad. The clinical disturbance of greatest importance is the association of mild hypomagnesemia with ventricular arrhythmia in patients with cardiac disease. At-risk patients include those with acute myocardial ischemia, congestive heart failure, or recent cardiopulmonary bypass, as well as acutely ill patients in the intensive care unit. 
The ionic basis of the effect of magnesium depletion on cardiac arrhythmia may be related to impairment of the membrane sodium-potassium pump and the increased outward movement of potassium through the potassium channels in cardiac cells, leading to shortening of the action potential and increasing susceptibility to cardiac arrhythmia. 
Torsade de pointes, a repetitive, polymorphous ventricular tachycardia with prolongation of the QT interval, has been reported in conjunction with hypomagnesemia, and the American Heart Association recommends that magnesium sulfate be added to the regimen used to manage torsade de pointes or refractory ventricular fibrillation.
40 Kelepouris E, Agus ZS. Hypomagnesemia: renal magnesium handling. Semin Nephrol. 1998 Jan. 18(1):58-73. [Medline].
41 Khan AM, Lubitz SA, Sullivan LM, Sun JX, Levy D, Vasan RS. Low serum magnesium and the development of atrial fibrillation in the community: the Framingham Heart Study. Circulation. 2013 Jan 1. 127(1):33-8. [Medline].
42 Ho KM, Sheridan DJ, Paterson T. Use of intravenous magnesium to treat acute onset atrial fibrillation: a meta-analysis. Heart. 2007 Nov. 93(11):1433-40. [Medline]. [Full Text].
43 Agus ZS, Morad M. Modulation of cardiac ion channels by magnesium. Annu Rev Physiol. 1991. 53:299-307. [Medline].
Item #10 and then more on Mg deficiency.
References to Magnesium Deficiency Research
Hypomagnesemia Clinical Presentation
Updated: Jun 16, 2017
•Author: Tibor Fulop, MD, FASN, FACP; Chief Editor: Vecihi Batuman, MD, FASN more...
Abnormalities of magnesium levels, such as hypomagnesemia, can result in disturbances in nearly every organ system and can cause potentially fatal complications (eg, ventricular arrhythmia, coronary artery vasospasm, sudden death). (See Pathophysiology.) Despite the well-recognized importance of magnesium, low and high levels have been documented in ill patients,  as a result of which, magnesium has occasionally been called the "forgotten cation." [2, 3] …. [emedicine.medscape.com]