New-Onset Atrial Fibrillation
And Myocardial Infarction
Several studies have evaluated the usefulness of admitting or obtaining enzymes in all patients with NOAF to "rule out" MI.42-46 In a small retrospective study, Friedman et al showed that all of the MIs (n=5) in the setting of NOAF could have been predicted on arrival to the ED from a set of high-risk criteria. These criteria included left ventricular hypertrophy, ECG evidence of old MI, cardiac-sounding chest pain, and cardiac symptoms of less than four hours.44 Friedman et al then prospectively examined a group of patients admitted with NOAF (without obvious evidence of MI on arrival) to identify risk factors associated with inhospital complications.42 Of note, 15% of the patients
admitted developed enzymatic evidence of non-Q-wave MI. Risk factors for complications (including MI) were signs of CHF on arrival and lack of conversion to normal sinus rhythm within six hours. Zimetbaum et al published a prospective cohort study in which they reported on 109 patients who underwent a standard "rule-out MI" protocol. 46 They found ECG changes to be the most important discriminator as to which patients were likely to develop MI. Chest pain was a very sensitive, but nonspecific, marker of MI. However, this study shows that those patients with NOAF and chest pain (how many don't have some chest pain?) require admission to evaluate for ischemia. After pooling the data from these studies and another retrospective study by Mulcahy et al,43 it does appear that some very select patients with NOAF are at low risk for MI and may not require admission. (See Table 8.) It is important to note that these criteria have not been prospectively evaluated.
Mulcahy et al published a study that specifically looked at NOAF patients and tried to address the question of when admission is medically justified.43 They looked retrospectively at 216 patients admitted to the hospital with NOAF. They believed that only 143/216 (66%) of the admissions were medically justified based on complications they had or developed in the hospital. Of the 143 patients who were ultimately classified as medically justified admissions, 140 (98%) could have been predicted from criteria fulfilled while in the ED. They suggested that patients with NOAF as the sole reason for admission (33% in this study) "can be managed as outpatients if they are hemodynamically stable and the ventricular rate can be controlled in the ED." However, the authors rightfully point out that their study was retrospective and should be validated in a prospective trial. It is interesting to note, however, that two of the three patients who would not have met the author's admission criteria, but were still admitted, died. In addition, patients categorized as not medically justified still spent several days in the hospital.128
So who are the truly low-risk patients who might go home safely? Suggested criteria at this time would include:
• younger patients (<60);
• patients without significant comorbid disease;
• patients in whom there is no clinical suspicion of PE or MI;
• patients in whom the AF converts in ED or the rate is controlled; and
• patients for whom follow-up is ensured.
The elderly and those with chest pain should usually be admitted. In some cases, patients may benefit from a brief workup (including cardiac enzymes and echocardiography) for risk stratification in an observational-type unit.129 In this unit, patients might be rate controlled, started on anticoagulation (possibly LMWH), and discharged to see if spontaneous conversion occurs. Upon follow-up, an outpatient TEE could guide further therapy and intervention.
Early follow-up is mandatory for all NOAF patients being discharged. Patients must be given good discharge instructions regarding the importance of follow-up and signs or symptoms that should prompt a return to the ED.