The objective of this research study is to test the accuracy of preexisting criteria versus expert interpretation for the diagnosis of acute coronary occlusion (major heart attack due to a completely blocked blood vessel). If our hypothesis proves to be true, this would provide a significant improvement in the care for patients who present to the hospital with possible symptoms of coronary ischemia (symptoms due to lack of blood flow to the heart).

The primary analysis will be designed as a multi-center, retrospective case-control study.

In this retrospective, 2-center, case-control study the investigators will investigate and compare the accuracy of various ECG criteria and expert interpretation to diagnose Acute Coronary Occlusion (ACO), with an emphasis on the diagnosis of patients with ACO but without obvious ST segment Elevation Myocardial Infarction (STEMI) criteria. The investigators will use two cohorts of patients who present with symptoms consistent with acute MI, one subsequently proven to have ACO and one proven to not have ACO.

The groups will be identified by chart reviewers who will use all clinical data except the ECGs to determine, in retrospect, and using strict criteria, if the patient had ACO at the time of the ECGs to be evaluated, or not. These reviewers will be blinded to all ECGs. The diagnosis of ACO will be dependent upon angiographic occlusion. Because in many cases of ACO, the artery spontaneously opens by the time of the angiogram, the investigators will need to have surrogate endpoints: this will be culprit on the angiogram PLUS a very elevated peak troponin, as peak troponin I > 10.0 ng/mL and peak troponin T > 1.0 ng/mL are highly correlated with ACO.

The investigators will find cases of subtle STEMI (ACO without STEMI criteria) by searching for all myocardial infarction cases that underwent angiography and percutaneous coronary intervention (PCI). The investigators will attempt by various criteria to determine from all available sources other than the ECG (angiography, echo, troponins) whether the involved artery was occluded at the time of the most diagnostic ECG that was recorded while the patient had symptoms and before the angiogram. Reviewers determining ACO or not ACO will be blinded to the ECGs. The investigators will use each pre-angiogram ECG, in sequence, for analysis, to determine if expert interpretation can not only identify occlusion that is not identified by STEMI criteria, but also to find if expert interpretation can identify occlusion on an earlier ECG. Expert ECG interpreters will interpret the ECG for evidence of ACO. Their accuracy will be compared to traditional STEMI criteria and other methods of interpretation if available.

The investigators will use as controls patients with any ST elevation, or ST depression, of any etiology that are proven to NOT have occlusion. The investigators will establish absence of occlusion by a combination of objective data points including angiogram (if performed), troponins, echocardiograms, clinical course, etc. Details of the methods are below, including specific outcome definitions used to claim the presence or absence of ACO.

Inclusion Criteria:

• Recorded EKG prior to cardiac catheterization

Exclusion Criteria:

• Absence of documented EKG prior to cardiac catheterization

The investigators plan to review and include all individuals that underwent urgent or emergent cardiac catheterization over the course of one year (January 1, 2017 - December 31, 2017).