AF and HF are frequently seen in the hospital setting. AF affects over 2 million people in the United States, while HF affects over 5 million. These disease states have a significant morbidity and mortality impact with AF leading to a 4 fold increase in stroke and 2 fold increase in death, while 50% of patients with a new HF diagnosis will die within 5 years. These two disease states share several common risk factors including, age, hypertension, diabetes mellitus, and heart disease. Based on this relationship and the changes in myocardial structure, function, and conduction the two are also risk factors for one another. Of patients with HF, 61.5% of men and 73% of women develop AF. Of those with AF, 73% of men and 75.6% of women develop HF.

Both the AF guidelines by the American Heart Association, American College of Cardiology, and Heart Rhythm Society and the HF guidelines by the American College of Cardiology Foundation and the American Heart Association recommend against the use of ND CCB in patients with HFrEF. The HF guidelines specify to avoid ND CCB in patients with reduced LVEF, but also mention avoiding most calcium channel blockers in general with the possible exception of amlodipine, due to known adverse effects and potential for harm. However, short term use of diltiazem for the acute control of RVR in patients with HFrEF has not been clearly evaluated. Three studies compare the use of BB and ND CCB in the acute treatment of AF RVR. These studies excluded those with severe (New York Heart Association Class IV) or decompensated HF, however, they did not comment on patients with compensated HFrEF. Most of these studies illustrate no difference, but the most recent study reported a success rate (heart rate (HR) \<100 bpm within 30 minutes) of 95.8% with intravenous (IV) diltiazem and 46.4% with IV metoprolol (p\<0.0001).

When comparing use of long term and short term therapy in patients with HFrEF a different perspective emerges. Both BB and ND CCB have negative inotropic effects which can be harmful during an acute HF exacerbation and worsen symptoms. However, BB are routinely recommended for chronic use in HFrEF due to their added neurohormonal benefit, which over time delays HF progression and reduces mortality. In contrast, long term treatment with ND CCB in those with pulmonary congestion is associated with an increased cumulative rate of cardiac events (hazard ratio 1.41). The comparative short term benefit in patients is still unclear. In a small study, patients with AF RVR and severe HF, 97% treated with IV diltiazem had a HR reduction of \>20% and no evidence of HF exacerbation. A second study of patients in decompensated HF compared the use of IV metoprolol and diltiazem for control of AF RVR. Both agents were equally effective at controlling heart rate with no difference in safety endpoint or evidence of worsening heart failure. Neither of these studies specifically address compensated HFrEF.

Current literature focuses on the risks associated with ND CCB and patients with HFrEF, but these effects are with long-term treatment. Studies in the acute setting often exclude those with severe or decompensated HFrEF. Therefore, a study focusing on metoprolol versus diltiazem for the acute control of AF RVR in patients with HFrEF could offer an insight into current clinical practice.