Usefulness of High-frequency QRS Analysis in the Evaluation of Patients With Chest Pain

Overview

Accurate detection of a heart attack (an acute myocardial infarction) is one of the most pressing needs in medicine. Recordings of the electrocardiogram (ECG) (electrical activity of the heart) are one of the first tools used to diagnose a heart attack, but the ECG is not very accurate, especially at the beginning of a heart attack. A new technique for analysing a special part of the ECG may provide more accurate detection of a heart attack. The study hypothesis is that this new technique, the HFQRS analysis, will provide important additional information to that available from the regular ECG.

Chest pain is one of the leading reasons for hospital emergency department (ED) visits worldwide. In the United States (US), over 6 million people annually undergo evaluation in the ED for acute chest pain. Despite the wealth of knowledge available about acute coronary syndrome (ACS), this condition continues to be among the most difficult to predict or diagnose. Nearly half of patients hospitalized for unstable angina eventually receive a non-cardiac-related diagnosis. Nonetheless, 2-8% of patients with myocardial infarction (MI) are inappropriately discharged from the ED and mortality rates among patients with an MI who were mistakenly sent home are disproportionately higher (25-33%) than those among patients who were admitted. Although the ECG is a mainstay in the management of suspected ACS, it has major limitations in both sensitivity and specificity for diagnosis of ACS. The initial 12-lead ECG in the ED is often non-diagnostic in ACS patients, especially in non-ST elevation MI (NSTEMI) and unstable angina (UA), and therefore cannot rule-out ischemia or infarction. Elevation in serum biomarkers is usually not detectable for 4-6 hours after an MI, and some patients do not show a biomarker elevation for as long as 12 hours. Consequently, new clinical tools for early risk stratification of patients with acute chest pain are being sought. Conventional analysis of ST segment deviations aims to detect repolarization abnormalities. However, ischemia may also bring about changes in the depolarization phase of the electrical cardiac cycle. These depolarization changes can be detected and quantified using analysis of the high-frequency components of the QRS complex (HFQRS). HFQRS analysis has been previously reported to be a sensitive method for detection of demand ischemia during exercise testing. Preliminary studies have shown that HFQRS-derived indices can also identify supply ischemia caused by prolonged balloon occlusion, and transient ischemic episodes in patients with chest pain.