Differentiation of acute inferior wall myocardial infarction caused by acute type A aortic dissection from atherosclerotic inferior myocardial infarction
Authors: Hirata K , Wake M , Tengan T , Taniguchi N , Ishimine T , Mototake H , Yamaguchi Y , Toyozato N , Takahashi T , Nakazato J , Yagi N , Miyagi T , Asato T , Shimabukuro Y 
Published: November 2023

Abstract

Background
Myocardial infarction (MI) caused by acute type A aortic dissection (AAD) is a rare but serious complication. To avoid unnecessary and possibly harmful treatment, differentiation of AAD-MI from atherosclerotic MI (AMI) is very important. However, there is a paucity of data regarding differentiation between AAD-MI and AMI.

Purpose
To compare the differences of clinical features between AAD-MI and AMI, and develop an effective way of differentiation.

Methods
Among 318 cases with AAD between 1982 and 2020, 18 cases (5.7%) had AAD-MI, of which 13 had inferior wall AAD-MI. Clinical features were compared with 25 consecutive inferior ST elevation AMI cases between 2017-2019. Categorial data and numerical data were compared using Fisher’s exact test and Student T test, respectively.

Results
Mean age and male/female ratio in AAD-MI and AMI were similar at 67.5 vs 66.3 years and 7/6 vs 13/12, respectively. The distribution of coronary risks factors and pain as presenting symptoms were similar in both groups. Initial systolic blood pressure (SBP) was significantly lower, and the incidence of shock was significantly higher in AAD-MI group compared to AMI group (SBP: 97.5 ± 26.4 vs 124.6 ± 32.7 mmHg, P = 0.014. shock: 9/13, 69.2% vs 5/25 20.0%, P = 0.0048). Although the heart rate was similar in both groups, AAD-MI group was more tachypnoeic than AMI group (27.8 ± 7.4 vs 22.7 ± 5.9/min, P = 0.046). All cases in both groups had ST elevation &gt;1mm in inferior leads (by definition). There were no differences of the degree of ST elevation (2.46 ± 1.19 vs 2.54 ± 1.50 mm. P = 0.87), and the incidence of arrhythmias such as AV block. Chest X-ray showed higher incidence of mediastinal widening (MW) in AAD-MI group compared to AMI group (11/13, 84.6% vs 5/25, 20.0%. P =0.0003), whereas the incidence rates of cardiomegaly and congestive heart failure were not different. Pulse deficit (PD) and hemiplegia were seen in AAD-MI group only (pulse deficit: 5/13, 38.5% vs 0/25, 0%. P = 0.0026. hemiplegia: 2/13, 15.4% vs 0/25, 0% P = 0.11). The incidence of tamponade (T) and aortic regurgitation (AR) were higher in AAD-MI group than in the AMI group (T: 7/13, 53.8% vs 0/25, 0%. p=0.00014. AR: 8/13, 61.5% vs 4/25 16.0% P = 0.009). The combination of either PD, AR, or T increased the sensitivity up to 84.6% while the specificity was 84.0%. Intimal flap was successfully identified by bedside echocardiography in 7 out of 9 cases (77.8%) in AAD-MI group.

Conclusion
ADD-MI and AMI present with similar risk factors, clinical symptoms, and electrocardiographic findings. However, ADD-MI cases were associated with worse findings, such as, lower initial SBP, tachypnoea and had higher incidences of shock, PD, MW, T, and AR compared to AMI cases. Echo is of critical importance as it can identify abnormalities more specific for AAD (AR, T) and can make final diagnosis of AAD through visualizing the intimal flap.Summary tableA representative case