This study revealed that the 12-year stroke rate in patients after AMI is significant higher in patients with AF than without AF, with a HR of 1.67. This negative impact was also found in both genders, different ages, and either receiving intervention (PCI or CABG) or not. In AF patients, preexisting AF has a significant higher stroke rate compared to new-onset AF in the subgroups of male genders, age below 65 years, and receiving intervention therapies.
New onset and preexisting AF in AMI
Our data revealed that the incidence of AF during hospitalization was 5% (8,530 in 170,472 patients) and the majority was new-onset AF (78%, 6,641 in 8,530 patients). According to the previous study, the incidence of AF during hospitalization for AMI was reported as a incidence ranging from 4–19%.7 The increased rate of AF can be resulted from an increased left atrial pressure.8 This can either be a direct consequence of atrial ischemia or be indirectly caused by an enhanced left ventricular filling pressure or a restricted left ventricular function.9, 10
In a previous study by Zusman et al., the new onset AF following myocardial infarction was associated with a nearly 35-fold increased risk of stroke during follow-up (mean 41 months; HR 34.6, 95% CI: 4.0-296.8).11 However, the limited number of patients and events (14 events out of 300 patients) made their results seem to be less precise, as evidenced by such a wide 95% CI. In a study with the use of data from Danish National Patients Registry with a total of 89,703 patients with myocardial infarction being analyzed and at the end of 5-year follow-up, new onset AF complicating myocardial infarction was demonstrated as an independent predictor for fetal and non-fetal stroke (HR: 2.34; 95% CI: 2.12–2.57 and HR: 2.47; 95% CI: 2.24–2.73, respectively).12 Additionally, Luo et al. reported a meta-analysis which showed that new-onset AF was associated with an increased risk of ischemic stroke (risk ratios: 2.84, 95% CI: 1.91–4.23; 6 studies).13 About preexisting AF, Tanne et al. reported that chronic AF was associated with significant appearance of stroke/TIA in hospital-discharged survivors of AMI (odds ratio: 5.71, 90% CI: 1.55–21.01).14 Our data included both patients with new-onset and preexisting AF, with a longer follow-up duration (up to 12 years) and a high amount of patients with AF (8,530 patients). The stroke risk after AMI in our study was significant higher in patients with AF than those without AF, with a HR of 1.67 (95% CI, 1.5–1.87).
AMI Patients with preexisting AF may have the presentation of previous diastolic dysfunction and cardiomyopathy. On the other hand, AMI patients with new-onset AF during is due to acute change at the time of AMI, including left atrial ischemia or overload, as well as neuroendocrine activation and tachycardia due to hemodynamic instability. Therefore, preexisting AF and new-onset AF may influence outcomes differently. To our knowledge, there was only one report directly compare preexisting and new-onset AF in the influence of stroke in patients with AMI by Gourronc el al. They have compared preexisting AF, new-onset AF and AF-free patients with AMI. The results showed that there was no significant difference in respect of stroke between preexisting AF, new-onset AF, and AF-free patients (2.2%, 0.5%, and 0.8%, respectively, p = 0.327).15 Our data showed that in AMI patients with AF, including new-onset and preexisting, have significant higher stroke rates as compared to those without AF. Our data was different from Gourronc et al. may be because that we have much more patients enrolled (8,530 AF patients in our study as compared to 436 patients with AF in their study) and much longer follow-up durations (up to 12 years in our study as compared to 1 year in their study).
Our study showed that in the subgroup of male, age younger than 65 years and with intervention therapies, AMI patients with prior AF have significant higher stroke rate in the subgroup than those with new-onset AF (Table 4). Besides, AMI patients with prior AF have higher ratios of female gender, older ages, NSTEMI, and heart failure and lower ratios of intervention therapies and dyslipidemia. The CHA2DS2-VASc scores were significant higher in prior AF group as compared to new-onset AF group. Lau et al. reported that in patients with acute coronary syndrome, those with prior AF had significant higher ratio of older ages, female gender and had significant lower ratio of intervention therapy.16 The results were compatible with our study. As a result, patients with prior AF tend to be more fragile and could explain the significant higher stroke rate in male, younger, and intervention therapy than patients with new onset AF.
There are several limitations in this study. First, although previous study had confirmed the accuracy of NHIRD as a valid resource for research of cardiovascular disease17, the relevant clinical variables such as cardiac biomarkers, left ventricular ejection fraction, and Killip grade were unavailable and these variables had important influences on the occurrence of stroke. Second, the type of AF did not present in this study. However, according to the previous study, the type of AF did not significantly affect the risk of stroke and should not influence the decision of stroke prevention.18 Third, the anticoagulation therapy in this study period for AF patients was mainly warfarin. However, non-Vitamin K oral anticoagulants are now used widely in the prevention of stroke in patients with AF and percentage of anticoagulants use has been largely increased in recent years.19 The clinical practice nowadays may affect the rates of stroke in patients with AF. However, it remains challenging issue to use antiplatelet and anticoagulant therapy in AMI patients with AF, which need to be investigated in further large-scale trail.