Electrocardiographic changes during prolonged coronary artery occlusion in man: comparison of standard and high-frequency recordings

COMPUTER MODELS OF DEPOLARIZATION ALTERATIONS INDUCED BY MYOCARDIAL ISCHEMIA: THE EFFECT OF SUPERIMPOSED ISCHEMIC INHOMOGENEITIES ON PROPAGATION IN SPACE AND TIME-FREQUENCY DOMAINS

A two-dimensional modified Luo-Rudy model was created to represent a 40 mm by 40 mm slab of myocardial tissue. An inhomogeneity was introduced to simulate acute myocardial ischemia, with components of hyperkalemia, acidosis and anoxia. Simulations were carried out for various degrees of ischemia, to study both the interaction of the propagation front with the inhomogeneity, and the reconstructed signals. The simulations utilized a modified LR model, with a realistic anisotropy of myocardial tissue. Each cluster (.4 mm ×.4 mm) was given bulk electric properties, Rx and Ry (25Ω and 250Ω, respectively). The slab was stimulated and the 2D depolarization pattern was computed by numerical integration. To study ischemia, a circular inhomogeneity with concentric regions (ro=12.8 mm{border zone, BZ} , ri=11.2 mm{extreme zone, EZ} ) regions was introduced in the model. From the 2D simulations and the regional action potentials (AP), unipolar and bipolar lead potentials were reconstructed. Time-frequency decomposition was performed on the lead signals by wavelet analysis. Isochrone and (dV/dt) max maps were obtained to study depolarization. Our results indicate that spatial inhomogeneities yield dramatic spatial dispersion of the wavefront and are the origin of mid-frequency intra-QRS components in cardiac signals. Severe APD shortening and spatial distortion of the isochrone and upstroke maps are also observed.

High-frequency electrocardiogram as a supplement to standard 12-lead ischemia monitoring during reperfusion therapy of acute inferior myocardial infarction

BACKGROUND

Resolution of ST-segment elevation in the electrocardiogram (ECG) is used as a reperfusion sign during thrombolytic therapy in acute myocardial infarction. Analysis of high-frequency QRS components (HF-QRS) might provide additional information. The study compares changes in HF-QRS (150-250 Hz) to ST-segment changes in the standard ECG during thrombolytic therapy.

METHODS

Twelve patients receiving intravenous thrombolytic therapy were included. A continuous 12-lead ECG recording was acquired for 4 hours.

RESULTS

After 1 hour of therapy, 3 patients showed ST-elevation resolution as well as an increase in HF-QRS. These changes in ST and HF-QRS occurred simultaneously. No other patient showed significant changes in ST or HF-QRS after 1 hour. After 2 and 4 hours, there was less concordance between the standard and high-frequency ECGs.

CONCLUSIONS

In patients with early ST-elevation resolution, the standard and high-frequency ECGs show similar results. Later changes are more disparate and may provide different clinical information.

High-frequency QRS electrocardiogram

The standard 12-lead electrocardiogram (ECG) is one of the most commonly used methods for diagnosing heart disease. Standard ECG is not always optimal, however, and new ECG methods can provide additional information. Analysis of high-frequency QRS components (HF-QRS) has been shown to increase the diagnostic performance of the ECG. Several investigators have studied HF-QRS in different cardiac conditions, including acute myocardial ischaemia and myocardial infarction, but more knowledge is needed about the characteristics of HF-QRS before clinicians can use it as an adjunct to standard ECG.

High-frequency electrocardiogram analysis in the ability to predict reversible perfusion defects during adenosine myocardial perfusion imaging

BACKGROUND

A previous study has shown that analysis of high-frequency QRS components (HF-QRS) is highly sensitive and reasonably specific for detecting reversible perfusion defects on adenosine myocardial perfusion imaging (MPI) scans. The purpose of the present study was to try to reproduce those findings.

METHODS

Twelve-lead high-resolution electrocardiogram recordings were obtained from 100 patients before (baseline) and during adenosine (99m)Tc-tetrofosmin MPI tests. The HF-QRS were analyzed regarding morphology and changes in root mean square voltages from before the adenosine infusion to peak infusion.

RESULTS

The best area under the curve (AUC) was found in supine patients (AUC = 0.736) in a combination of morphology and root mean square changes. None of the measurements, however, were statistically better than tossing a coin (AUC = 0.5).

CONCLUSION

Analysis of HF-QRS was not significantly better than tossing a coin for determining reversible perfusion defects on MPI scans.

Reduced high-frequency QRS components in electrocardiogram leads facing an area of the heart with intraventricular conduction delay due to bundle branch block

BACKGROUND

The mechanisms underlying high-frequency QRS components (HF-QRS) are incompletely understood. One theory is that HF-QRS are related to the conduction velocity of the heart. The purpose was to test this hypothesis by comparing HF-QRS in patients with left or right bundle branch block (LBBB and RBBB, respectively) to those in healthy subjects and in patients with ischemic heart disease (IHD).

METHODS

Twenty-two patients with LBBB, 19 patients with RBBB, 63 normal subjects, and 64 patients with IHD were included. Twelve-lead electrocardiograms were analyzed in the frequency interval 150 to 250 Hz.

RESULTS

The study showed reduced HF-QRS in patients with LBBB compared with healthy subjects and patients with IHD. The difference, however, was small in lead V(1) and V(2). In patients with RBBB, no differences in HF-QRS could be detected except in few leads; among those is lead V(1).

CONCLUSION

The results support the theory that HF-QRS are related to the conduction velocity of the heart.

Lack of impact of myocardial ischemia on the signal-averaged ECG assessment by time-domain analysis

BACKGROUND

Late potentials represent an arrhythmogenic substrate in chronically infarcted myocardium. It is hypothesized that acute transient ischemia enhances anisotropic electrical ventricular activation and facilitates reentry mechanisms. Study aim was the prospective assessment of the impact of dipyridamole-induced myocardial ischemia on the signal-averaged ECG.

METHODS

Dipyridamole stress thallium-201 SPECT imaging was utilized to avoid noise contamination of the signal-averaged ECG from exercise and to document evidence and localization of myocardial ischemia or persistent perfusion defects in 68 patients with suspected coronary artery disease. Before and during dipyridamole-induced vasodilatation serial signal-averaged ECG was performed to evaluate the influence of transient ischemia on the occurrence of late potentials.

RESULTS

There was a significant difference between heart rate at rest and heart rate under dipyridamole influence in patients with inducible ischemia (70 +/- 13 vs. 87 +/- 13; P < 0.0001) in contrast to patients without dipyridamole-induced ischemia (74 +/- 20 vs. 80 +/- 16; n.s.). The number of averaged beats and achieved noise level was comparable between both groups. Thirty-three of 68 patients (49%) revealed dipyridamole-induced ischemia; however, no changes of the SAECG parameters, such as QRS, RMS, LAS at 25-250 and 40-250 Hz bandpass filtering in the leads X, Y, Z and vector magnitude, respectively, were observed as a result of ischemia.

CONCLUSION

These results suggest that transient myocardial ischemia does not affect the signal-averaged ECG. Clinically, the signal-averaged ECG analysis seems not to be helpful in identifying patients with silent ischemia.

Determination of the ability of high-frequency ECG to estimate left ventricular mass in humans, determined by magnetic resonance imaging

BACKGROUND

Previous studies have shown a significantly higher correlation between left ventricular mass index (LVMi) and high-frequency QRS components (HF-QRS) than between LVMi and QRS amplitudes in the standard frequency range in rabbits. The purpose of the present study was to compare ECG measurements from standard and high-frequency ranges with left ventricular mass (LVM) and LVMi determined by magnetic resonance imaging in humans.

METHODS

Sixty-two normal subjects were studied. Signal-averaged ECGs from the 12 standard leads were analysed in the standard frequency range (0.05-150 Hz), in the middle (25-100 Hz) and high end (50-150 Hz) of the standard frequency range and in the 150-250 Hz range. Root-mean square (RMS) values from the HF-QRS and QRS amplitude measurements from the standard ECGs were compared with LVM and LVMi.

RESULTS

The correlations between LVMi and HF-QRS were similar to those between LVMi and standard ECG. When regarding LVM, however, the correlations found in the standard ECG were higher than those found in HF-QRS.

CONCLUSIONS

Contrary to previous results in animals, we found in humans no better correlation between HF-QRS and LVM/LVMi than between standard ECG and LVM/LVMi.

High-frequency QRS electrocardiogram predicts perfusion defects during myocardial perfusion imaging

BACKGROUND

Changes in high-frequency (HF) QRS components of the electrocardiogram (ECG) (150-250 Hz) are more sensitive than changes in conventional ST segments for detecting myocardial ischemia. We investigated the accuracy of 12-lead HF QRS ECG in detecting perfusion defects during adenosine tetrofosmin myocardial perfusion imaging (MPI).

METHODS AND RESULTS

12-lead HF QRS ECG recordings were obtained from 45 patients before and during adenosine technetium Tc 99m tetrofosmin MPI tests. Before the adenosine infusions, recordings of HF QRS were analyzed according to a morphologic score that incorporated the number, type, and location of reduced amplitude zones (RAZs) present in the 12 leads. During the adenosine infusions, recordings of HF QRS were analyzed according to the maximum percentage changes (in both the positive and negative directions) that occurred in root mean square voltage amplitudes within the 12 leads. The best set of prospective HF QRS criteria had a sensitivity of 94% and a specificity of 83% for correctly identifying the MPI result. The sensitivity of simultaneous ST-segment changes (18%) was significantly lower than that of any individual HF QRS criterion (P < .001).

CONCLUSIONS

Analysis of 12-lead HF QRS ECG is highly sensitive and reasonably specific for detecting perfusion defects during adenosine MPI stress tests and significantly more sensitive than analysis of conventional ST segments.

Twelve-lead high-frequency QRS electrocardiography during anesthesia in healthy subjects

Analysis of the high-frequency (HF) components of the QRS complex has been shown to be a more sensitive indicator of myocardial ischemia and infarction than conventional ST segment analysis in settings outside of the operating room. In this study, we documented the effect of general anesthesia on HF QRS analysis in healthy patients as the first step in determining the potential of this technique for monitoring anesthetized patients. HF QRS electrocardiograms (ECGs) were obtained from all 12 ECG leads in 30 healthy subjects before and after the induction of anesthesia. When compared with preinduction values, there were significant postinduction changes in multiple variables of the HF QRS in many leads studied that were within previously described normal limits. Additional study is needed to understand the potential of this monitoring technique for enhancing detection of myocardial ischemia in the anesthetized population.

Reduced high-frequency QRS components in patients with ischemic heart disease compared to normal subjects

Analysis of high-frequency QRS components (HF-QRS) might provide an additional method when diagnosing various heart diseases, for example ischemic heart disease (IHD). This study compares HF-QRS in normal subjects to those in patients with IHD, and also analyzes HF-QRS considering gender and age. A total of 63 normal subjects and 64 patients with IHD were included. Signal-averaged electrocardiograms (ECGs) from the 12 standard leads were analyzed in the frequency interval of 150-250 Hz. The results showed that the summed 12 lead HF-QRS in patients with IHD were significantly lower than in normal subjects (mean summed HF-QRS was 33.5 microV in the IHD group, 43.7 microV in normal individuals, P <.0005). HF-QRS were not statistically associated with gender or age (P =.820 and P =.573, respectively). However, the inter-individual variation of HF-QRS was large in both groups which probably limits the clinical usefulness of the method.

High-frequency components in ECG analysed in guinea-pig Langendorf preparations

High-frequency components in ECG during global ischaemia were studied in isolated guinea-pig hearts perfused ad modum Langendorf. Electrocardiograph recordings were carried out from the epicardial surface both in normo- and low-flow perfusion. After bandpass filtering (5-500 Hz), signal-averaging, was undertaken. The high-frequency components either increased or decreased after low-flow perfusion was instituted. Root-mean-square voltage (RMS) of the depolarization signal correlated poorly with the signal amplitude, but highly with the first and second derivative, i.e. the velocity and the acceleration of the signal. It is concluded that high-frequency components are not pathological phenomena per se, but reflect the shape of the original electrocardiographic signal.

The absence of high-frequency QRS changes in the presence of standard electrocardiographic QRS changes of old myocardial infarction

BACKGROUND

This study compares the high-frequency QRS components (HF-QRS) in patients with and without standard electrocardiogram (ECG) changes indicative of old myocardial infarction (MI). Previous studies have indicated that patients with an old MI differ in their HF-QRS compared with healthy subjects. The HF-QRS has been reported to be decreased during acute coronary occlusion and increased after reperfusion. However, there is controversy about the appearance of HF-QRS after the acute phase of MI.

METHODS

A total of 154 patients were included, 57 with and 97 without QRS changes of old MI on the standard ECG. The patients with old MI were divided into subgroups on the basis of the MI location indicated by the standard ECG. Signal-averaged ECGs from the 12 standard leads were recorded. The root-mean-square values of the HF-QRS were determined within two frequency bands: 150 to 250 Hz and 80 to 300 Hz.

RESULTS

There was a large interindividual variation in HF-QRS in patients without MI as well as in those with different MI locations. There were no significant differences between the groups in the summed HF-QRS of all 12 leads or in the pattern of lead distribution of the HF-QRS. Not even the patients with the greatest QRS changes of old MI could be differentiated from those without any changes of old MI on the standard ECG. The results were the same in both analyzed frequency bands.

CONCLUSIONS

This study shows, contrary to previous studies, that analysis of HF-QRS cannot differentiate between patients with and without old MI.

Changes in high-frequency QRS components are more sensitive than ST-segment deviation for detecting acute coronary artery occlusion

OBJECTIVES

This study describes changes in high-frequency QRS components (HF-QRS) during percutaneous transluminal coronary angioplasty (PTCA) and compares the ability of these changes in HF-QRS and ST-segment deviation in the standard 12-lead electrocardiogram (ECG) to detect acute coronary artery occlusion.

BACKGROUND

Previous studies have shown decreased HF-QRS in the frequency range of 150-250 Hz during acute myocardial ischemia. It would be important to know whether the high-frequency analysis could add information to that available from the ST segments in the standard ECG.

METHODS

The study population consisted of 52 patients undergoing prolonged balloon occlusion during PTCA. Signal-averaged electrocardiograms (SAECG) were recorded prior to and during the balloon inflation. The HF-QRS were determined within a bandwidth of 150-250 Hz in the preinflation and inflation SAECGs. The ST-segment deviation during inflation was determined in the standard frequency range.

RESULTS

The sensitivity for detecting acute coronary artery occlusion was 88% using the high-frequency method. In 71% of the patients there was ST elevation during inflation. If both ST elevation and depression were considered, the sensitivity was 79%. The sensitivity was significantly higher using the high-frequency method, p<0.002, compared with the assessment of ST elevation.

CONCLUSIONS

Acute coronary artery occlusion is detected with higher sensitivity using high-frequency QRS analysis compared with conventional assessment of ST segments. This result suggests that analysis of HF-QRS could provide an adjunctive tool with high sensitivity for detecting acute myocardial ischemia.