Quantifying QRS changes during myocardial ischemia: Insights from high frequency electrocardiography

Revisiting the diagnostic and prognostic significance of high-frequency QRS analysis in cardiovascular diseases: a comprehensive review

Cardiovascular diseases (CVDs) present a significant global public health threat, contributing to a substantial number of cases involving morbidity and mortality. Therefore, the early and accurate detection of CVDs plays an indispensable role in enhancing patient outcomes. Decades of extensive research on electrocardiography at high frequencies have yielded a wealth of knowledge regarding alterations in the QRS complex during myocardial ischemia, as well as the methodologies to assess and quantify these changes. In recent years, the analysis of high-frequency QRS (HF-QRS) components has emerged as a promising non-invasive approach for diagnosing various cardiovascular conditions. Alterations in HF-QRS amplitude and morphology have demonstrated remarkable sensitivity as diagnostic indicators for myocardial ischemia, often surpassing measures of ST-T segment changes. This comprehensive review aims to provide an intricate overview of the current advancements, challenges, and prospects associated with HF-QRS analysis in the field of CVDs.

The combination of high-frequency QRS and ST-segment alterations during exercise stress tests enhanced the diagnostic efficacy for coronary artery disease

BACKGROUND

High-frequency QRS (HF-QRS) manifests as a novel adjunct electrocardiographic marker with potential utility in coronary artery disease (CAD) detection.

HYPOTHESIS

We hypothesize that HF-QRS analysis may be superior to conventional ST-segment analysis in detecting CAD, and the combination of these two analyses in the exercise stress test may enhance the diagnostic efficacy for CAD.

METHODS

The study incorporated a sample of 157 patients (mean age 62 ± $\pm $  9 years) referred for nonemergent angiography. Before angiography, patients underwent exercise stress testing utilizing an upright bicycle. High-resolution electrocardiogram (ECG) data were collected during the exercise test, facilitating both HF-QRS and conventional ST-segment analyses. The diagnostic efficacy of HF-QRS and ST-segment analysis were compared, utilizing angiographic outcomes as the gold standard. The study design integrated HF-QRS analysis and ST-segment analysis via sequential and concurrent testing protocols.

RESULTS

In terms of CAD detection, HF-QRS analysis displayed superior sensitivity compared to conventional ST-segment analysis (63% vs. 37%, p = .002). The serial test significantly increased specificity from 79% to 97% (p = .002) compared to ST-deviation analysis alone. It showed a markedly low sensitivity of 26%. The parallel test significantly increased sensitivity from 37% to 77% (p < .001), while retaining a moderate level of specificity of 51%. The quantity of ECG leads exhibiting a positive HF-QRS response demonstrated a correlation with the severity of CAD (p < .001).

CONCLUSIONS

HF-QRS analysis exhibited superior sensitivity in detecting angiographically confirmed CAD relative to conventional ST-segment analysis. Moreover, the combination of HF-QRS and ST-segment alterations during exercise stress test enhanced the diagnostic efficacy for CAD.

Changes in High-Frequency Intracardiac Electrogram Indicate Cardiac Ischemia

High-frequency QRS (HFQRS) analysis of surface ECG is a reliable marker of cardiac ischemia (CI). This study aimed to assess the response of HFQRS signals from standard intracardiac electrodes (iHFQRS) to CI in swine and compare them with conventional ST-segment deviations. Devices with three intracardiac leads were implanted in three swine in a controlled environment. CI was induced by inflating a balloon in epicardial coronary arteries. A designated signal-processing algorithm was applied to quantify the iHFQRS content before, during, and after each occlusion. iHFQRS time responses were compared to conventional ST-segment deviations. Thirty-three over thirty-nine (85%) of the occlusions presented significant reduction in the iHFQRS signal, preceding ST-segment change, being the only indicator of CI in brief occlusions. iHFQRS was found to be an early indicator for the onset of CI and demonstrated superior sensitivity to conventional ST-segment deviations during brief ischemic episodes.

High-frequency QRS analysis to supplement ST evaluation in exercise stress electrocardiography: Incremental diagnostic accuracy and net reclassification

BACKGROUND

Exercise stress electrocardiography (ECG) alone is underutilized in part due to poor diagnostic accuracy. High-frequency QRS analysis (HF-QRS) is a novel tool to supplement ST evaluation during stress ECG. We compared the diagnostic accuracy and net reclassification of HF-QRS analysis compared with ST evaluation for substantial myocardial ischemia by exercise SPECT myocardial perfusion imaging (MPI).

METHODS AND RESULTS

Exercise SPECT MPI was performed in 257 consecutive eligible patients (mean age 59 ± 12, 67% male). An ischemic HF-QRS pattern was defined as a ≥ 1 µV absolute reduction and a ≥ 50% relative reduction of the root-mean-square of the 150-250 Hz band signal in ≥ 3 leads. Left ventricular ischemia of ≥ 10% on SPECT MPI was the diagnostic standard for substantial myocardial ischemia. HF-QRS analysis demonstrated incremental diagnostic value to ST evaluation plus clinical risk factors (AUC 0.804 vs 0.749, P < .0001). A HF-QRS + ST -analysis strategy identified 92.3% of subjects with substantial ischemia and no abnormality in 59.9% of the cohort. No cardiac events occurred in patients without substantial ischemia identified by HF-QRS analysis.

CONCLUSIONS

In this prospective analysis, exercise stress ECG with HF-QRS analysis identified any and substantial ischemia with high diagnostic accuracy and may allow more than half of referred patients to safely avoid imaging.

High-Frequency ECG for Detection of Myocardial Ischemia Associated with Right Coronary Artery Stenosis in IHD Patients

The aim of the investigation was to study the parameters of high-frequency ECG in leads V1, V3R, V4R, V5R, V6R as additional diagnostic criteria for detecting the areas of myocardial ischemia associated with stenosis of the right coronary artery (RCA) in IHD patients.

MATERIALS AND METHODS

The study involved 47 patients who underwent selective coronary angiography (SCA) for detection of IHD. The patients were divided into two groups based on the SCA results: group 1 included 28 patients with hemodynamically significant RCA stenosis; group 2 consisted of 19 patients with hemodynamically non-significant RCA stenosis. Prior to SCA, all patients underwent resting high-frequency ECG recording in 12 conventional leads and in leads V3R-V6R for 5 min. The study also involved 15 volunteers with no history of cardiovascular disease or IHD symptoms (control group) who underwent ECG in the same leads. The resulting data were processed and analyzed using the ArMaSoft-12-Cardio software (©ArMaSoft, 1995-2019, Russia), which made it possible to determine the presence or absence of reduced amplitude zones (RAZ) of the QRS complex in all morphological variants, the root-mean-square (RMS) deviation, and excess kurtosis.

RESULTS

Statistically significant differences in the RAZ parameter of the QRS complex were revealed in high-frequency ECG of patients with hemodynamically significant and non-significant RCA stenosis. The RAZ sum in leads V1, V3R, V4R, V5R, V6R was 7.86±0.77 and 3.58±0.53, respectively, while in patients with no IHD signs, it equaled 1.87±0.43 (p=0.00001).The RMS value in patients with no IHD signs was 3.89±0.42, in patients with hemodynamically non-significant and significant RCA stenosis it equaled 3.51±0.34 and 2.73±0.24, respectively (p=0.008).The kurtosis value was statistically significantly higher in patients with hemodynamically significant stenosis (1.07±0.12), in contrast to those with hemodynamically non-significant stenosis and without IHD (0.78±0.05 and 0.64±0.03, respectively).An average correlation between the value of coronary stenosis and the sum of RAZ scores was found (r=0.66).However, RMS and kurtosis parameters correlate with the degree of RCA stenosis at a lower level.According to ROC analysis, the RAZ parameter showed better diagnostic results compared to RMS and kurtosis. Given the nonparametric nature of the available data, the prognostic capabilities of the studied parameters can be considered satisfactory as shown by the results of binary logistic regression.

CONCLUSION

The RAZ parameter of high-frequency ECG in leads V1, V3R, V4R, V5R, V6R may serve as an additional diagnostic criterion for identifying the areas of myocardial ischemia associated with RCA stenosis in IHD patients.

A Case of Acute Coronary Occlusion in a Morbidly Obese Patient Masked on Electrocardiogram by Low QRS Voltage

Timely diagnosis of acute coronary occlusion is essential to avoid chronic cardiac impairment and death. We describe an uncommon case of acute myocardial infarction masked by low QRS voltage secondary to morbid obesity. This case highlights the importance of considering the degree of ST-segment elevation proportionally to the QRS amplitude if there is clinical suspicion of acute coronary occlusion.

Functional aging in health and heart failure: the COmPLETE Study

BACKGROUND

Cardiovascular (CV) diseases including heart failure are the leading causes of morbidity, with age being the primary risk factor. The combination of age-related organic functional impairment and reduced physical fitness can drastically impact an individual's healthspan. One's lifespan can potentially be prolonged by the preservation or improvement of physical fitness. However, it remains unclear as to which biomarkers are most suitable for distinguishing between healthy aging and the impaired organ function associated with heart failure. Therefore, a comprehensive assessment of the components of physical fitness and CV function will be performed to identify the most important factors contributing to aging in relation to both health and disease.

METHODS

This cross-sectional investigation will consist of two parts: COmPLETE-Health (C-Health) and COmPLETE-Heart (C-Heart). C-Health will examine the aging trajectories of physical fitness components and CV properties in a healthy population sample aged between 20 and 100 years (n = 490). Separately, C-Heart will assess the same markers in patients at different stages of chronic heart failure (n = 80). The primary outcome to determine the difference between C-Health and C-Heart will be cardiorespiratory fitness as measured by cardiopulmonary exercise testing on a bicycle ergometer. Secondary outcomes will include walking speed, balance, isometric strength, peak power, and handgrip strength. Physical activity as a behavioural component will be assessed objectively via accelerometry. Further, CV assessments will include pulse wave velocity; retinal, arterial, and venous diameters; brachial and retinal arterial endothelial function; carotid intima-media thickness; and systolic and diastolic function. The health distances for C-Health and C-Heart will be calculated using the methodology based on statistical (Mahalanobis) distance applied to measurements of quantitative biomarkers.

DISCUSSION

This research seeks to identify physical fitness and CV biomarkers that best resemble underlying CV risk with age. Further, it will examine which physical fitness markers are impaired most in heart failure. The presented integrative approach could define new recommendations for diagnostic guidance in aging. Ultimately, this study is expected to offer a better understanding of which functional characteristics should be specifically targeted in primary and secondary prevention to achieve an optimal healthspan.

Analysis of the High-Frequency Content in Human QRS Complexes by the Continuous Wavelet Transform: An Automatized Analysis for the Prediction of Sudden Cardiac Death

BACKGROUND

Fragmentation and delayed potentials in the QRS signal of patients have been postulated as risk markers for Sudden Cardiac Death (SCD). The analysis of the high-frequency spectral content may be useful for quantification.

METHODS

Forty-two consecutive patients with prior history of SCD or malignant arrhythmias (patients) where compared with 120 healthy individuals (controls). The QRS complexes were extracted with a modified Pan-Tompkins algorithm and processed with the Continuous Wavelet Transform to analyze the high-frequency content (85-130 Hz).

RESULTS

Overall, the power of the high-frequency content was higher in patients compared with controls (170.9 vs. 47.3 10³nV²Hz^-1; p = 0.007), with a prolonged time to reach the maximal power (68.9 vs. 64.8 ms; p = 0.002). An analysis of the signal intensity (instantaneous average of cumulative power), revealed a distinct function between patients and controls. The total intensity was higher in patients compared with controls (137.1 vs. 39 10³nV²Hz^-1s^-1; p = 0.001) and the time to reach the maximal intensity was also prolonged (88.7 vs. 82.1 ms; p < 0.001).

DISCUSSION

The high-frequency content of the QRS complexes was distinct between patients at risk of SCD and healthy controls. The wavelet transform is an efficient tool for spectral analysis of the QRS complexes that may contribute to stratification of risk.

ECG features and methods for automatic classification of ventricular premature and ischemic heartbeats: A comprehensive experimental study

Accurate detection of cardiac pathological events is an important part of electrocardiogram (ECG) evaluation and subsequent correct treatment of the patient. The paper introduces the results of a complex study, where various aspects of automatic classification of various heartbeat types have been addressed. Particularly, non-ischemic, ischemic (of two different grades) and subsequent ventricular premature beats were classified in this combination for the first time. ECGs recorded in rabbit isolated hearts under non-ischemic and ischemic conditions were used for analysis. Various morphological and spectral features (both commonly used and newly proposed) as well as classification models were tested on the same data set. It was found that: a) morphological features are generally more suitable than spectral ones; b) successful results (accuracy up to 98.3% and 96.2% for morphological and spectral features, respectively) can be achieved using features calculated without time-consuming delineation of QRS-T segment; c) use of reduced number of features (3 to 14 features) for model training allows achieving similar or even better performance as compared to the whole feature sets (10 to 29 features); d) k-nearest neighbours and support vector machine seem to be the most appropriate models (accuracy up to 98.6% and 93.5%, respectively).

High-frequency power within the QRS complex in ischemic cardiomyopathy patients with ventricular arrhythmias: Insights from a clinical study and computer simulation of cardiac fibrous tissue

BACKGROUND

The distribution of frequency power (DFP) within the QRS complex (QRS) is unclear. This study aimed to investigate the DFP within the QRS in ischemic cardiomyopathy (ICM) with lethal ventricular arrhythmias (L-VA). A computer simulation was performed to explore the mechanism of abnormal frequency power.

METHODS

The study included 31 ICM patients with and without L-VA (n = 10 and 21, respectively). We applied the continuous wavelet transform to measure the time-frequency power within the QRS. Integrated time-frequency power (ITFP) was measured within the frequency range of 5-300 Hz. The simulation model consisted of two-dimensional myocardial tissues intermingled with fibroblasts. We examined the relation between frequency power calculated from the simulated QRS and the fibroblast-to-myocyte ratio (r) of the model.

RESULTS

The frequency powers significantly increased from 180 to 300 Hz and from 5 to 15 Hz, and also decreased from 45 to 80 Hz in patients with ICM and L-VA compared with the normal individuals. They increased from 110 Hz to 250 Hz in ICM alone. In the simulation, the high-frequency power increased when the ratio (r) were 2.0-2.5. Functional reentry was initiated if the ratio (r) increased to 2.0.

CONCLUSIONS

Abnormal higher-frequency power (180-300 Hz) may provide arrhythmogenic signals in ICM with L-VA that may be associated with the fibrous tissue proliferation.

Ventricular dyssynchrony assessment using ultra-high frequency ECG technique

Purpose

The aim of this proof-of-concept study is to introduce new high-dynamic ECG technique with potential to detect temporal-spatial distribution of ventricular electrical depolarization and to assess the level of ventricular dyssynchrony.

Methods

5-kHz 12-lead ECG data was collected. The amplitude envelopes of the QRS were computed in an ultra-high frequency band of 500–1000 Hz and were averaged (UHFQRS). UHFQRS V lead maps were compiled, and numerical descriptor identifying ventricular dyssynchrony (UHFDYS) was detected.

Results

An electrical UHFQRS maps describe the ventricular dyssynchrony distribution in resolution of milliseconds and correlate with strain rate results obtained by speckle tracking echocardiography. The effect of biventricular stimulation is demonstrated by the UHFQRS morphology and by the UHFDYS descriptor in selected examples.

Conclusions

UHFQRS offers a new and simple technique for assessing electrical activation patterns in ventricular dyssynchrony with a temporal-spatial resolution that cannot be obtained by processing standard surface ECG. The main clinical potential of UHFQRS lies in the identification of differences in electrical activation among CRT candidates and detection of improvements in electrical synchrony in patients with biventricular pacing.

Electronic supplementary material

The online version of this article (doi:10.1007/s10840-017-0268-0) contains supplementary material, which is available to authorized users.

Diagnostic and Prognostic Value of Lead aVR During Exercise Testing in Patients Suspected of Having Myocardial Ischemia

We aimed to assess the diagnostic and prognostic value of ST-segment deviation in aVR, a lead often ignored in clinical practice, during exercise testing and to compare it to the most widely used criterion of ST-segment depression in V₅. We enrolled 1,596 patients with suspected myocardial ischemia referred for nuclear perfusion imaging undergoing bicycle stress testing. ST-segment amplitudes in leads aVR and V₅ were automatically measured. The presence of inducible myocardial ischemia was the diagnostic end point and adjudicated based on nuclear perfusion imaging and coronary angiography. Major adverse cardiac events (MACE) during 2 years of follow-up including death, acute myocardial infarction, and coronary revascularization were the prognostic end point. Exercise-induced myocardial ischemia was detected in 470 patients (29%). Median ST amplitudes for leads aVR and V₅ differed significantly among patients with and without ischemia (p <0.01). The diagnostic accuracy of ST changes for myocardial ischemia as quantified by the area under the receiver operating characteristic curve was highest 2 minutes into recovery and similar in aVR and V₅ (0.62, 95% confidence interval CI 0.60 to 0.65 vs 0.60, 95% confidence interval 0.58 to 0.63, p = 0.08 for comparison). In multivariate analysis, ST changes in lead aVR, but not lead V₅, contributed independent diagnostic information on top of clinical parameters and manual electrocardiographic interpretation. Within 2 years of follow-up, MACE occurred in 33% of patients with ST elevations in aVR and in 16% without (p <0.001). In conclusion, ST elevation in lead aVR during exercise testing indicates inducible myocardial ischemia independently of ST depressions in lead V₅ and clinical factors and also predicts MACE during follow-up.

Diagnostic value of ST-segment deviations during cardiac exercise stress testing: Systematic comparison of different ECG leads and time-points

BACKGROUND

Exercise ECG stress testing is the most widely available method for evaluation of patients with suspected myocardial ischemia. Its major limitation is the relatively poor accuracy of ST-segment changes regarding ischemia detection. Little is known about the optimal method to assess ST-deviations.

METHODS

A total of 1558 consecutive patients undergoing bicycle exercise stress myocardial perfusion imaging (MPI) were enrolled. Presence of inducible myocardial ischemia was adjudicated using MPI results. The diagnostic value of ST-deviations for detection of exercise-induced myocardial ischemia was systematically analyzed 1) for each individual lead, 2) at three different intervals after the J-point (J+40ms, J+60ms, J+80ms), and 3) at different time points during the test (baseline, maximal workload, 2min into recovery).

RESULTS

Exercise-induced ischemia was detected in 481 (31%) patients. The diagnostic accuracy of ST-deviations was highest at +80ms after the J-point, and at 2min into recovery. At this point, ST-amplitude showed an AUC of 0.63 (95% CI 0.59-0.66) for the best-performing lead I. The combination of ST-amplitude and ST-slope in lead I did not increase the AUC. Lead I reached a sensitivity of 37% and a specificity of 83%, with similar sensitivity to manual ECG analysis (34%, p=0.31) but lower specificity (90%, p<0.001).

CONCLUSION

When using ECG stress testing for evaluation of patients with suspected myocardial ischemia, the diagnostic accuracy of ST-deviations is highest when evaluated at +80ms after the J-point, and at 2min into recovery.

Ambulatory monitoring of myocardial ischemia in the 21st century-an opportunity for high frequency QRS analysis

Ambulatory monitoring represents an effective tool for the assessment of silent and transient myocardial ischemia during routine daily activities. Incidence of silent ischemia can provide important prognostic information about patients with coronary artery disease or acute coronary syndrome, as well as about post-myocardial infarction patients. The current technological progress enables development of powerful and miniaturized wearable devices for Holter monitoring. Higher sampling rates, dynamic range, and extended computational and storage capacity allow for considering of more complex methodological solutions such as high-frequency QRS analysis for diagnosing myocardial ischemia. Implementation of suitable methodologies for advanced detection of myocardial ischemia into modern ambulatory monitoring devices creates the potential of making the ambulatory myocardial ischemia monitoring a valuable diagnostic tool in clinical practice.

Can we hear ventricle dyssynchrony? Yes, we can

This study introduces a method for detection of ventricular depolarization activity and the transfer of this activity into an audible stereo audio signal. Heart potentials are measured by an ultra-high-frequency high-dynamic-range electrocardiograph (UHF-ECG) with a 25-kHz sampling rate. Averaged and prolonged UHF amplitude envelopes of V1-3 and V4-6 leads at a frequency range of 500-1000 Hz are used as a modulating function for two carrier audio frequencies. The right speaker makes it possible to listen to the depolarization of the septum and right ventricle (V1-3) and the left speaker the left ventricle lateral wall (V4-6). In the healthy heart, both speakers can be heard simultaneously. A delayed L or R speaker represents the dyssynchronous electrical activation of the ventricles. Examples of the normal heart, right bundle branch block and left bundle branch block can be heard at www.medisig.com/uhfecg.

Intra-QRS spectral changes accompany ST segment changes during episodes of myocardial ischemia

BACKGROUND

Coronary artery disease and myocardial ischemia cause substantial morbidity and mortality. While ischemia is traditionally diagnosed on the 12-lead electrocardiogram (ECG) by shifts in the ST segment, electrical changes are also produced within the QRS complex during depolarization of ischemic ventricular tissue, though these are often of small amplitude and can be missed in traditional ECG analysis. We explore the utility of an easily implemented spectral analysis method for detecting intra-QRS changes during episodes of myocardial ischemia, using Holter recordings from the European ST-T database.

METHODS

Time-frequency distributions of QRS complexes from each recording were computed using the continuous wavelet transform. Indices corresponding to frequency content of four overlapping frequency bands were computed: F1 (24-35Hz), F2 (30-45Hz), F3 (40-60Hz), and F4 (50-80Hz). Values of these indices were compared during annotated episodes of ST change and during a baseline during the recording.

RESULTS

Marked changes in intra-QRS frequency content were identified during ischemia, grouped by ECG lead analyzed. In lead III, a pronounced and statistically significant increase in the highest frequency sub-bands (F3 and F4) was consistently observed. Analysis of anterior precordial leads also showed significant increases in F4.

CONCLUSIONS

Intra-QRS time-frequency analysis using the continuous wavelet transform can identify a spectral signature corresponding to myocardial ischemia in the range 24-80Hz. Intra-QRS spectral analysis has the potential for many clinical applications.