Question: How does miR-1 overexpression contribute to arrhythmias in cardiac conditions?

Context:
Dysfunction of the gap junction protein connexin 43 (Cx43), an established miR-1 target, during cardiac hypertrophy leads to ventricular tachyarrhythmias (VT).
miR-1 overexpression may contribute to the increased susceptibility of the heart to AVB, which provides us novel insights into the molecular mechanisms underlying ischemic cardiac arrhythmias.
The incidence of AVB was higher in miR-1 Tg mice than that in wild-type (WT) mice. 
As miR-1 has been shown in animal models and clinical studies to contribute to arrhythmogenesis by regulating pacemaker channel genes, our finding of miR-1 up-regulation in patients with myocardial infarction indicates that it might be responsible for the higher risk for arrhythmias in these patients. 
Lately, some highlight articles revealed that the altered expression of miRNAs such as miR-1, miR-133, miR-21, miR-208 etc in hearts also contributed to cardiovascular diseases, such as heart ischemia, cardiac hypertrophy, and arrhythmias.
MicroRNA-1 (miR-1) reciprocally regulates inwardly rectifying potassium channel (Kir)2.1 expression in coronary disease, contributing to arrhythmogenesis. 
miR-1 levels are greatly reduced in human AF, possibly contributing to up-regulation of Kir2.1 subunits, leading to increased I(K1). Because up-regulation of inward-rectifier currents is important for AF maintenance, these results provide potential new insights into molecular mechanisms of AF with potential therapeutic implications.
The muscle-specific miR-1 has been implicated in cardiac hypertrophy, heart development, cardiac stem cell differentiation, and arrhythmias through targeting of regulatory proteins. 
We conclude that the beta-adrenergic pathway can stimulate expression of arrhythmogenic miR-1, contributing to ischaemic arrhythmogenesis, and beta-blockers produce their beneficial effects partially by down-regulating miR-1, which might be a novel strategy for ischaemic cardioprotection.
MiR-1 influences susceptibility to cardiac arrhythmias after myocardial infarction.
Changes in abundance of muscle-specific microRNA, miR-1, have been implicated in cardiac disease, including arrhythmia and heart failure.
In the presence of isoproterenol, rhythmically paced, miR-1-overexpressing myocytes exhibited spontaneous arrhythmogenic oscillations of intracellular Ca(2+), events that occurred rarely in control myocytes under the same conditions.
Here we show that miR-1 is overexpressed in individuals with coronary artery disease, and that when overexpressed in normal or infarcted rat hearts, it exacerbates arrhythmogenesis. Elimination of miR-1 by an antisense inhibitor in infarcted rat hearts relieved arrhythmogenesis.
 Thus, miR-1 may have important pathophysiological functions in the heart, and is a potential antiarrhythmic target.
MiR-1 influences susceptibility to cardiac arrhythmias after myocardial infarction
The muscle-specific miR-1 has been implicated in cardiac hypertrophy, heart development, cardiac stem cell differentiation, and arrhythmias through targeting of regulatory proteins
Changes in abundance of muscle-specific microRNA, miR-1, have been implicated in cardiac disease, including arrhythmia and heart failure
Changes in abundance of muscle-specific microRNA, miR-1, have been implicated in cardiac disease, including arrhythmia and heart failure

Answer: miR-1 overexpression may contribute to the increased susceptibility of the heart to AVB, which provides us novel insights into the molecular mechanisms underlying ischemic cardiac arrhythmias. The muscle-specific miR-1 has been implicated in cardiac hypertrophy, heart development, cardiac stem cell differentiation, and arrhythmias through targeting of regulatory proteins. MiR-1 influences susceptibility to cardiac arrhythmias after myocardial infarction. Changes in abundance of muscle-specific microRNA, miR-1, have been implicated in cardiac disease, including arrhythmia and heart failure. In the presence of isoproterenol, rhythmically paced, miR-1-overexpressing myocytes exhibited spontaneous arrhythmogenic oscillations of intracellular Ca(2+), events that occurred rarely in control myocytes under the same conditions. Here we show that miR-1 is overexpressed in individuals with coronary artery disease, and that when overexpressed in normal or infarcted rat hearts, it exacerbates arrhythmogenesis. Elimination of miR-1 by an antisense inhibitor in infarcted rat hearts relieved arrhythmogenesis. Thus, miR-1 may have important pathophysiological functions in the heart, and is a potential antiarrhythmic target.