The number of patients with cardiovascular implantable electronic devices (CIED), including ventricular pacemakers, continues to increase. However, there are no accurate electrocardiographic (ECG) criteria to diagnose acute myocardial infarction (AMI), even if due to acute coronary occlusion (ACO), with a ventricular pacemaker in situ. In this retrospective, multicenter, case-control study the investigators will examine ECG criteria to diagnose ACO in patients with ventricular paced rhythms. During this process, the investigators will also create a database from which investigators will be able to answer multiple additional questions on this population of patients.

BACKGROUND Diagnosis and management of ACO (the anatomic substrate for ST-elevation myocardial infarction) is time sensitive. Diagnosis necessitates emergent reperfusion therapy. An important predictor of death from ACO includes time to reperfusion.1 Delays in reperfusion therapy, including primary percutaneous coronary intervention (PCI) or fibrinolysis, are associated with worse 30-day and 1-year mortality. American Heart Association (AHA) guidelines for treatment of ACO recommend that the first medical contact to device time be less than 120 minutes in patients who have no contraindications to treatment.2 Though cardiac biomarkers are helpful in making the diagnosis in uncertain cases, the time sensitive nature of intervention for ACO precludes their use to direct emergent reperfusion therapy. Furthermore, biomarkers do not diagnose ACO but rather any AMI, including those without occlusion that do not need emergent intervention.

The "traditional" ECG diagnosis of ACO, which includes ST-elevation cutoffs based upon age and sex, excludes patients with ventricular paced rhythm (VPR).3 The small field of research on the topic of ACO in VPR has extrapolated and analyzed data from patients with left bundle branch block (LBBB). That is because VPR with right ventricular pacing and LBBB both result in depolarization from right to left through myocardium (not through conducting fibers) and thus result in similar ECG findings (e.g. wide QRS, delayed onset of depolarization, and abnormal repolarization with "discordant" [in the opposite direction of the QRS] T-waves and ST-segment deviation). In the presence of known LBBB, AHA guidelines recommend using the Sgarbossa criteria to make the diagnosis of ACO.4 Sgarbossa et al. proposed requiring at least 3 points from the following criteria for the diagnosis of acute myocardial infarction in the presence of LBBB: (1) concordant ST-segment elevation of 1 mm (0.1 mV) in at least 1 lead (5 points), (2) concordant ST-segment depression of at least 1 mm in leads V1 to V3 (3 points), or (3) excessively discordant ST-segment elevation, defined as greater than or equal to 5 mm of ST-segment elevation when the QRS complex is negative (2 points). There have been only a handful of evaluations of Sgarbossa's criteria in VPR, with variable methodologies and patient populations; sensitivities in the studies ranged from 10-53% and specificities ranged from 84-99%.5,6 Neither study used angiographic endpoints, but only used biomarker definitions of AMI; one study used a very flawed biomarker definition with no adjudication. Thus, the number of occlusions is entirely unknown and probably very small.

For LBBB, Smith et al. derived and validated a "modified Sgarbossa rule" in which they replaced Sgarbossa's third criterion (excessively discordant ST elevation as defined by 5 mm) with a proportion-based criterion (defined by > 25% of the previous S-wave) (see Table 1). This rule resulted in much higher sensitivity and accuracy for diagnosis of ACO than the original Sgarbossa.7,8

Table 1: MODIFIED SGARBOSSA CRITERIA

1. ST-segment elevation >= 1 mm and concordant with the QRS in any lead
2. ST-segment depression >= 1 mm and concordant with the QRS in any of leads V1- V3
3. Proportionally excessive discordant ST-segment elevation in at least one lead, as defined by ST/S (\

Inclusion Criteria:

• 18 year old at least, ischemic symptoms (e.g., chest pain, shortness of breath, etc.), ventricular paced rhythm on the Electrocardiogram (ECG).

Exclusion Criteria:

• Exclusion from Primary Analysis:

  1. Extreme tachycardia (heart rate > 130 bpm) at the time of presentation
  2. Severe hypertension (diastolic blood pressure > 120 mmHg) at the time of presentation
  3. Respiratory failure (defined as need for positive pressure ventilation) due to pulmonary edema at the time of presentation.
  4. Hyperkalemia (serum potassium > 5.5 mEq/L) at the time of presentation.

I. Adults who presented either 1) directly through the Emergency Department (ED), 2) as a transfer or referral patient, or 3) as a direct ambulance admission to the Catheterization Laboratory, who also:

1. Underwent urgent or emergent coronary angiography during the index presentation for suspected ischemic symptoms, and
2. Had a ventricular paced rhythm (VPR) on the ECG
3. Had sufficient troponins to rule in or rule out acute myocardial injury, per the study site's institutional protocol.

II. Next, each study site will identify all adult ED patients with a VPR ECG recorded during the index presentation who presented with suspected ischemic symptoms. Simple random selection will be used to identify subjects from this population. There may be overlap between this group and the angiogram group above and this will be considered at the data analysis stage (see Procedures Manual for more detail).

The first group will not be a probability sample, but the second group will be.