Myocardial infarction in patients with normal coronary arteries: proposed pathogenesis and predisposing risk factors

Risk factor comparison in young patients presenting with acute coronary syndrome with atherosclerotic coronary artery disease vs. angiographically normal coronaries

Background: Acute myocardial infarction is a relatively rare phenomenon in the young population. The incidence has nevertheless increased from years past, likely due to the presence of multiple risk factors from an increasingly younger age. Regardless of whether they have atherosclerotic coronary artery disease or normal coronary angiogram, young patients with risk factors for coronary artery disease (CAD), chest pain, and positive troponin, are initially treated in a similar fashion. Our goal was to shed light on whether risk factors between these two groups differ to help guide physicians in clinically determining whether or not an atherosclerotic cardiovascular event has occurred, as well as to potentially identify young patients at risk of acute coronary syndrome (ACS) despite normal coronary arteries. Methods: A retrospective cross sectional study was undertaken over an 8 year period at Tawam Hospital. 576 patients aged 50 or under who underwent coronary angiography were selected for the study. Medical records were analyzed for the patient's demographics and CAD risk factor profile, including the following variables: family history of CAD, smoking status, Body Mass Index category, lipid profile, and diagnosis of hyperlipidemia, diabetes, or hypertension. Details of the coronary angiogram were also reviewed. Results: Statistically significant outcomes included a higher prevalence of diabetes, hyperlipidemia, and smoking history in patients with CAD compared to the patients with normal coronary angiogram. Diabetes was one of the strongest risk factors in CAD patients, with an odds ratio of 1.98 (p= 0.011), followed by hyperlipidemia at 1.85 (p= 0.021). Smoking history had an odds ratio of 2.93 (p <0.001). Conclusion: Risk factors were present in both groups, but significantly more in the CAD group. No particular risk factor stood out for the development of ACS in those with normal coronary arteries, other than mean BMI being slightly higher in this group. Based on our analysis, no single variable can accurately predict the risk for ACS in normal coronaries. To our knowledge, few studies have been done in the young population with angiographically normal coronary arteries to determine possible risk factors for development of ACS. Further research needs to be done to determine whether the risk factors that were common amongst both groups are coincidental, or a cause of ACS in those with normal coronary arteries.

Myocardial Infarction Without Obstructive Coronary Artery Disease is Not a Benign Condition (ANZACS-QI 10)

BACKGROUND

Non-obstructive coronary artery disease (CAD) on coronary angiography after myocardial infarction (MI) is associated with a lower risk of adverse outcomes, but the prognosis may not be benign. Our aim was to assess outcomes in MI with and without obstructive CAD, and in an age and sex matched comparison cohort without known cardiovascular disease.

METHODS

We performed a single centre analysis of consecutive patients undergoing coronary angiography for MI between 2007 and 2012. Patients were classified into those with obstructive CAD (≥50% epicardial coronary artery stenosis) and those without obstructive CAD (<50%). Myocardial infarction patient data was collected in an electronic registry and linked anonymously to national hospitalisation and mortality records. Age and sex matched patients without known CVD were identified from the community PREDICT cohort.

RESULTS

Of the 2070 patients with MI, 302 (15%) had non-obstructive CAD. Compared to patients with obstructive disease they were younger (mean 57 v 61 years, p<0.001), more likely to be women (50% vs 23%, p<0.001), to be of Maori or Pacific vs. European ethnicity (p<0.001), more likely to be lifelong non-smokers (46% v 38%, p=0.02), non-diabetic (80v 73%, p <0.01), have no ST-segment deviation (78% v 46%, p<0.001), and have a low risk Global Registry of Acute Coronary Events acute coronary syndrome (GRACE ACS) score (54 v 35%, p<0.001). They were also less likely to receive 'triple therapy' secondary prevention medications (81% v 94%, p<0.0001). The cumulative two-year Kaplan-Maier composite outcome of mortality or non-fatal MI was 14.3% for MI with obstructive CAD, 4.6% for MI without obstructive disease, and 2.2% for patients without prior CVD (p<0.001).

CONCLUSION

Myocardial infarction without obstructive coronary disease is common (∼1 in 7 patients) and is not clinically benign, with an adverse outcome rate double that of age and sex matched patients without CVD.

Cardiogenic shock without flow-limiting angiographic coronary artery disease: (from the Should We Emergently Revascularize Occluded Coronary Arteries for Cardiogenic Shock Trial and Registry)

Myocardial infarction often develops when thrombosis occurs at lesions that have not previously been flow limiting. However, the development of cardiogenic shock complicating acute myocardial infarction in such circumstances has received little attention. The characteristics of 15 patients with cardiogenic shock who had no flow-limiting angiographic stenoses were compared with those of 767 patients with > or =1 stenosis who were enrolled in the Should We Emergently Revascularize Occluded Coronary Arteries for Cardiogenic Shock (SHOCK) trial and registry. Compared with patients with > or =1 flow-limiting stenosis, patients with no flow-limiting stenoses were less likely to have pulmonary edema on chest x-ray (29% vs 62%, p = 0.008) and to be white (53% vs 82%, p = 0.011), and they had lower median highest creatine kinase levels (702 vs 2,731 U/L, p = 0.018). For SHOCK trial patients, 1-year survival was 49% for patients with > or =1 flow-limiting stenosis and 71% for those with no flow-limiting stenoses (p = 0.268). In conclusion, patients with cardiogenic shock without flow-limiting stenosis have different characteristics, and potentially disease mechanisms, and they do not require revascularization.