High-frequency QRS analysis in patients with acute myocardial infarction: a preliminary study

Abstract

Background: The 12-lead electrocardiogram (ECG) is a primary tool in the evaluation and risk stratification of patients with suspected acute myocardial infarction (AMI), even though the initial ECG of these patients is often normal or nondiagnostic. Myocardial ischemia induces depolarization changes that can be quantified by analysis of high-frequency QRS (HFQRS) components. We aimed to demonstrate the potential usefulness of HFQRS analysis in diagnosing myocardial ischemia by characterizing the morphological patterns of the HFQRS signals in patients with AMI before and following reperfusion.

Methods: Five-minute high-resolution ECG was acquired from 30 patients with AMI (age 55 ± 11 years, 26 men) upon their admission to the intensive coronary care unit (ICCU). Serial ECGs were acquired following coronary revascularization and after additional 24 hours (24h). High-frequency morphology index (HFMI), quantifying the extent of ischemic patterns was computed by a custom software, and its values were compared between the serial ECG measurements.

Results: HFMI values were significantly higher on the admission ECG as compared to the post intervention ECG (4.6 ± 2.9% vs 3.4 ± 2.3%, P < 0.05) and to the 24h ECG (4.6 ± 2.9% vs 2.8 ± 2.1%, P < 0.01). In 79% of the patients who were successfully revascularized HFMI value decreased from admission ECG to 24h ECG.

Conclusions: Analysis of HFQRS morphology in patients with AMI provides information about the existence and severity of myocardial ischemia. HFQRS analysis may aid in risk stratification of patients with suspected myocardial ischemia, complementarily to conventional ECG.

Trial registration: ClinicalTrials.gov NCT01150825.

©2012, Wiley Periodicals, Inc.

Figures

Figure 1

Flowchart of the study protocol. AMI = acute myocardial infarction; ICCU = intensive coronary care unit; PCI = percutaneous coronary intervention; HFQRS = high‐frequency QRS.

Figure 2

Principles of high‐frequency QRS (HFQRS) analysis. (A) QRS complexes are detected while rejecting arrhythmias and noisy complexes. (B) The detected QRS complexes are aligned and averaged to suppress noise. (C) Filtering in the 140–250 Hz frequency band produces the HFQRS signal. (D) HFQRS signal envelope is calculated and reduced area zones (RAZ) are detected and quantified. (E) An index of ischemia is calculated based on RAZ quantification in all 12 leads (E).

Figure 3

ECG and HFQRS signals acquired at admission, post revascularization, and after 24 hours from a 41‐year‐old male with ST‐elevation MI. Note the profound change in the HFQRS signal morphology, showing a significant reduced amplitude zone (RAZ) during admission, which is resolved after 24 hours. Conventional ECG does not exhibit ischemic pattern.

Figure 4

Comparison of average HFMI values at ICCU admission, post angiography, and after 24 hours. Error bar represent standard error of the mean. HFMI = high‐frequency morphology index; angio. = angiography; STEMI = ST elevation myocardial infarction; Urgent reperf. = urgent reperfusion; Spont reperf. = spontaneous reperfusion.

Figure 5

ECG and HFQRS signals of a 30‐year‐old patient with perimyocarditis and symptoms of acute MI. Resting ECG at ICCU admission (A) shows significant ST‐elevation, whereas HFQRS signals (B) reveal normal signal morphology, with mild RAZ pattern in only one lead (V3). Angiography demonstrated normal coronary arteries.