Prehospital ECG diagnostic algorithm for STEMI in HK: High sensitivity, fair specificity

A rule-based prehospital electrocardiogram (PHECG) algorithm universally utilized in Hong Kong for diagnosis of ST-elevation myocardial infarction (STEMI) should not be solely relied on for primary diversion of patients with chest pain to centres capable of primary percutaneous coronary intervention (PCI), as the algorithm is highly sensitive but only fairly specific, a study has shown.

The prospective observational study analyzed data from a territory-wide audit of the Prehospital 12-Lead Electrocardiogram for Chest Pain Protocol led by the Hospital Authority (HA) Coordinating Committee in Accident and Emergency. The Protocol, jointly launched on 1 February 2021 by HA and the Hong Kong Fire Services Department, entails performance of 12-lead ECG on scene or in a stationary ambulance compartment for all patients with complaints of chest pain, excluding those who were below 12 years of age, in cardiac arrest, with unmanageable airway or breathing, having a Glasgow Coma Scale score of ≤13, a first systolic blood pressure of <90 mm Hg, a respiratory rate of <10 or >29 breaths per minute, or refused or unable to give consent. [Hong Kong Med J 2024;doi.org/10.12809/hkmj2310827]

A total of 2,334 PHECGs carried out between 1 October and 31 December 2021 were analyzed to determine the diagnostic performance of the PHECG algorithm for STEMI. Overall, 62.9 percent of the patients were male, mean age of the patients was 67.7 years, and 405 (17.4 percent) PHECGs were classified as STEMI by the algorithm. In total, 83.6 percent of patients were placed on stretchers upon arrival at the emergency department (ED).

Using adjudicated blinded rating by two investigators as the reference standard, the study found that the rule-based PHECG algorithm had a sensitivity of 94.6 percent (95 percent confidence interval [CI], 88.2–97.8 percent), specificity of 87.9 percent (95 percent CI, 86.4–89.2 percent), positive predictive value of 29.4 percent (95 percent CI, 24.8–34.4 percent), and negative predictive value of 99.7 percent (95 percent CI, 99.3–99.9 percent) (all p<0.05).

Due to possibility of false-positive or false-negative results, the investigators underscored the importance of clinical judgment in conjunction with algorithmic assessments in optimizing patient care and outcomes.

“One in eight ECGs showed false-positive results for STEMI, with early repolarization [38 percent], left bundle branch block [15.7 percent], and extreme tachycardia [>140 beats per minute; 13.3 percent] being the leading causes,” the investigators reported.

“The findings indicate that primary diversion of STEMI patients to PCI-capable centres should not be implemented solely based on the PHECG algorithm’s diagnosis,” they suggested. “A hybrid two-step ECG interpretation model, involving a physician’s remote interpretation of ECGs that are classified as STEMI by the computerized algorithm, could be adopted to minimize overactivation and ensure prudent use of healthcare resources.”

While STEMI can be reasonably excluded by the PHECG diagnostic algorithm due to its high negative predictive value, evolving ECG patterns, subtle ST-segment elevation, and STEMI equivalents were found to be responsible for false-negative diagnoses (STEMI missed by the algorithm using diagnosis on hospital discharge as the reference standard). “Hence, physicians should be aware of STEMI equivalents that are not identified by the algorithm,” noted the investigators.