In a U.S. study of 1,070 low-risk chest pain patients, MACE occurred in 0.6 percent (95% CI, 0.2–1.1%) of patients with a HEART score of 0–3 within 30 days.⁷ Use of the HEART score to guide patient disposition would have resulted in 5 cases of missed ACS (0.5 percent) and a potential cardiac function testing/imaging decrease of 82 percent. Functional testing was routinely performed in the observation unit where these patients were treated, and 94 percent had an exercise stress ECG, dobutamine stress ECG, coronary CT angiogram, or stress cardiac MRI. ECG stress testing without imaging was not performed, nor was technetium or sestamibi myocardial perfusion imaging.

Whether a 30-day to six-week time frame for MACE to develop (what about six months?) is reasonable or whether one in 60 to 167 patients meets the “acceptable miss rate” are reasonable concerns. It should be noted that, given the extraordinary low yield of positive stress tests/imaging studies, some have concluded that they not be performed in low-risk HEART score patients, despite the 2010 recommendation of the AHA/ACC (which were not changed in the 2015 update) that further testing occur within 72 hours in discharged patients.^8,9

In 2015, a head-to-head randomized comparison of the HEART pathway and usual care (as based on ACC/AHA recommendations) was conducted.¹⁰ A total of 282 patients with chest pain suspicious of ACS but with ECGs negative for ST elevation took part. With the HEART pathway, patients stratified to low risk (0–3) and who had negative standard-sensitivity troponins at zero and three hours of arrival were discharged without further testing, but were advised to follow up with their primary provider. When compared with usual care, the low-risk patients treated via the HEART pathway had decreased testing at 30 days by 12 percent, a shorter length of stay by nine hours in the hospital, and increased early discharge of 21 percent. No patient identified for early discharge had a MACE within 30 days.

Too good to be true? There are a few caveats. The clinicians were all at one academic facility and were not bound to follow the HEART pathway. Nonadherence to the HEART pathway occurred in 26 percent of the cases, although adherence in these cases would still have been associated with a 0 percent 30-day MACE rate in that no patient who was discharge via the HEART pathway or usual care had a MACE within 30 days. Also, the 30-day MACE rate for all the patients in the study was only 6 percent, and all occurred during the initial admission. Finally, there was a moderate bit of “kick the can down the road” in that further testing occurred during follow up in 57 percent of the low-risk HEART score patients versus 69 percent of usual care patients, so the absolute decrease in testing was small.

2015 Summary of Most Recent Medication Recommendations of the AHA and ACC for ACS

There was an extensive update of the AHA recommendations in 2015.⁹ Below are some changes from the 2010 guidelines. Updates regarding aspirin (ASA), nitroglycerine, and morphine were not included.

• Adenosine diphosphate receptor (ADP) inhibitors: In STEMI patients undergoing PCI, dual antiplatelet agents in advance improves clinical outcomes. An option to provide these medications in the prehospital setting is noted, but there seems to be no advantage over giving them in the emergency department. No recommendation regarding which ADP inhibitor to use is made. The assumption is made that all patients have receive 180 mg of non-enteric coated ASA.
• Unfractionated heparin
  • In the setting of a STEMI patient anticipated to have a PCI, prehospital administration is a reasonable option, as is enoxaparin.
• Routine Supplemental Oxygen
  • In normoxic ACS patients, the benefit of supplemental oxygen has not been established. Withholding oxygen may be associated with minimally reduced infarction size.
• Fibrinolytic Therapy
  • Prehospital administration is reasonable if transport times exceed 30 minutes in patients with a STEMI and they are going to a hospital where thrombolytic treatment is the standard.
  • If a STEMI patient is being taken to a PCI center, prehospital fibrinolytic therapy is without evidence of benefit and associated with a small risk of intracranial bleeding.

2017 Summary of the European Guidelines for Managing AMI with ST-Segment Elevation

The ESC released a total update of the guidelines for ST-segment and non-STEMI infarctions.11 It now advises:

• Left and right bundle branch block are considered equal for recommending urgent angiography if ischemic symptoms are of “STEMI diagnosis.”
  • PCI is preferred over thrombolysis if the time to get a wire across the clot is 120 minutes or less from time zero.
  • The maximum delay time from “STEMI diagnosis” to bolus of fibrinolysis is 10 minutes.
  • The “door-to-balloon” phase is eliminated.

Over the last 50 years there have been remarkable gains in the management of ACS. Mortality of STEMI patients is now in the range of 4 to 5 percent when just 50 years ago it was in the teens. Now there is active curative therapy, while in the past, palliative therapy (rest) was really the only treatment.