Detection and localization of prolonged epicardial electrograms with 64-lead body surface signal-averaged electrocardiography

Magnetocardiographic mapping of QRS fragmentation in patients with a history of malignant tachyarrhythmias

BACKGROUND

The identification of patients at increased risk for ventricular tachycardia or ventricular fibrillation (VT/VF) and sudden cardiac death has consequences for therapeutic options and thus may reduce mortality in patients with coronary artery disease (CAD).

HYPOTHESIS

We hypothesized that the intra-QRS fragmentation in magnetocardiographic recordings is increased in patients with CAD and with a history of VT/VF.

METHODS

Multichannel magnetocardiography (MCG) was carried out in 34 healthy controls, 42 patients with CAD without a history of VT/VF, and 43 patients with CAD and with a history of VT/VF. The intra-QRS fragmentation was quantified by a new fragmentation score. Its spatial distribution was investigated using two-dimensional (2-D) contour maps according to the sensor position of the 49-channel magnetogradiometer.

RESULTS

Patients with CAD and with a history of VT/VF had significantly increased QRS fragmentation compared with patients with CAD without VT/VF or controls (72.9+/-37.5, 48.5+/-14.3, and 42.5+/-7.8, respectively: p <0.05). The area of high fragmentation in 2-D contour maps was twice as large in patients with than in those without a history of VT/VF (represented by the number of MCG channels with high fragmentation: 26.3+/-15.5 vs. 12.4+/-9.9, p<0.0001). Patients prone to VT/VF could be identified with a sensitivity of 64% and a specificity of 90%.

CONCLUSION

In patients with CAD and with a history of VT/VF, intra-QRS fragmentation is increased and the area of high fragmentation in 2-D contour maps is enlarged. These findings may be helpful in identifying patients with CAD at risk for malignant tachyarrhythmias.

Late QRS activity in signal-averaged magnetocardiography, body surface potential mapping, and orthogonal ECG in postinfarction ventricular tachycardia patients

BACKGROUND

Delayed electrical activity necessary for re-entrant ventricular tachycardia (VT) is detectable noninvasively with high resolution techniques. We compared high resolution signal-averaged analysis of magnetocardiography (MCG), body surface potential mapping (BSPM), and orthogonal three-lead ECG (SA-ECG) in the identification of patients prone to VT after myocardial infarction (MI).

METHODS

Patients with remote myocardial infarction and cardiac dysfunction were studied, 22 with (VT group) and 22 without VT (control group). MCG with seven channels and BSPM with 63 and SA-ECG with three orthogonal leads were registered. After signal-averaging and highpass filtering, three time domain analysis (TDA) parameters describing late electrical activity were computed: QRS duration (QRSd), root mean square amplitude (RMS) of the last 40 ms of QRS, and the duration of the low-amplitude QRS end (LAS).

RESULTS

All parameters by each method were significantly different between the patients' groups. For example, LAS parameter in MCG was 59 (SD 22) ms in the VT group vs. 37 (SD 13) ms in controls (P < 0.001), 77 (SD 22) ms vs. 56 (SD 19) ms in BSPM (P = 0.002), and 60 (SD 24) ms vs. 39 (SD 22) ms in SA-ECG (P = 0.005). The combination of LAS parameter in MCG and SA-ECG resulted in improved performance in comparison to any single parameter with 95% sensitivity and 68% specificity.

CONCLUSIONS

All three high resolution methods identified VT propensity among post-MI patients with cardiac dysfunction and between-method differences were small. Information in MCG and SA-ECG may be complementary and their combination could be of value in postinfarction arrhythmia risk assessment.

Localization of late potential sources in myocardial infarction

INTRODUCTION

Late potentials (LP) are markers of arrhythmogenic events after myocardial infarction (MI). The localization of LP sources would help to identify arrhythmogenic myocardium. The purpose of this study was to localize these LP sources from non-invasive body surface mapping data.

METHODS AND RESULTS

Six patients were investigated with cardiac MRI and signal averaged 62-lead magnetocardiography after MI. Three of them were suffering from sustained ventricular tachycardia (VT). Sophisticated computer algorithms were used in order to compute the current density on the surface of the left ventricle. We compared these current density distributions for the entire QRS complex and the high frequency LP signals. In the three patients which had premature ventricular complexes (PVCs) we localized the exit sites of these arrhythmias. We found a close matching of the low current density areas based on the QRS complexes and the high current density areas based on the LP signals. These areas predominantly corresponded to sites of the infarctions. Exit sites of PVCs were located close to these areas.

CONCLUSIONS

By means of sophisticated computer algorithms we were able to localize LP sources. This would be useful in steering catheter ablation and coronary revascularization therapies. However, the method has to be proven with the help of invasive mapping in a larger number of patients.

Relation between spatial distribution of late potentials and location of origin of premature ventricular complexes on body surface map in patients with postinfarction ventricular tachycardia

We studied the relationship between the spatial distribution of late potentials (LPs) and the origin of premature ventricular complexes (PVCs) using body surface maps in 55 patients with postinfarction sustained ventricular tachycardia (VT). Body surface maps were recorded from 87 leads to construct departure maps during sinus rhythm and signal-averaged ECGs were recorded from 32 unipolar leads to construct a LP map. The root-mean-square values during 40 ms intervals behind the QRS end were computed as LPs. The PVC map was recorded simultaneously in 14 patients presenting PVC with similar morphology to VT during LP detection. The origin of PVC was localized at the site of isopotential minimum when the potential exceeded -0.5 mV during the early QRS period. The LP area and the departure area showed a similar distribution. However, the PVC origin was closer to the site of LP maximum than the departure minimum in 11 (79%) patients, and the spatial correlation between the LP maximum and the PVC origin was good in 12 (86%) patients. LP and PVC mapping from the body surface is feasible and of worth to predict noninvasively the site of origin of ventricular arrhythmias in patients with remote myocardial infarction and sustained VT.

Voltage sum of filtered ECG signal--a sensitive parameter of ventricular activation

On the basis of the signal averaged ECG (SA ECG) principle the authors analyse the gradually filtered ECG signal (in ranges of 0-120 Hz with increments of 10 Hz). The voltage sums are determined in eight segments of the QRS complex. The described VSF-ECG method (Voltage Sum of Filtered ECG) was applied in a group of healthy probands and in groups of selected patients. The measurements in healthy probands were used to determine the value of standard in healthy subjects. Repeated measurements confirmed a good reproducibility of the VSF-ECG method. The method enables a precise quantification of heart activation progression. VSF-ECG is a method revealing the changes of heart activation progression being not reflected as late potentials. Parameters of the method are indicators of activation splitting upon the infarction area and also an indicator of the electric milieu of the entire heart.

Electrocardiographic predictors in the ESVEM trial: unsustained ventricular tachycardia, heart period variability, and the signal-averaged electrocardiogram

Sudden death remains a major problem because the causes are uncontrolled and accurate predictors have not been identified. However, new forms of electrocardiographic (ECG) analyses may provide prognostic information. The Electrophysiologic Study Versus Electrocardiographic Monitoring (ESVEM) trial provides a unique perspective to this issue because baseline and follow-up data were prospectively acquired on a relatively large sample of patients who were homogeneous with respect to sustained ventricular tachyarrhythmias, frequent ectopic activity, and inducible sustained ventricular tachyarrhythmias. Although analysis of the large amount of ECG data collected is in progress, initial studies have provided information about unsustained ventricular tachycardia (VTu), heart period (R-R) variability, and the signal-averaged ECG. VTu has been reported to have prognostic implications in several disorders, but its clinical significance in patients with sustained ventricular tachyarrhythmias is unknown. The significance of VTu recorded in the baseline (antiarrhythmic drug-free) 48-hour ECG recording in ESVEM study patients was examined; no variable representing the presence of VTu, the frequency of VTu events, or the duration of the longest episode of VTu was a significant predictor of arrhythmia recurrence, arrhythmic death, or all-cause mortality, although a trend was present for worse all-cause mortality in patients with VTu. R-R variability provides powerful prognostic information after acute myocardial infarction (AMI) and in patients with chronic ischemic heart disease. In general, R-R variability decreases dramatically at the time of AMI and recovers somewhat during the year after infarction. Although most patients in the ESVEM trial had chronic ischemic heart disease, R-R variability, which has been determined in about three fourths of the patients, was much lower than that reported in patients 1 year after MI. Instead, the mean values were closer to the more depressed values observed shortly after MI. This suggests a greater degree of autonomic dysfunction in patients with sustained ventricular tachyarrhythmias, frequent ventricular ectopic activity, and low ejection fractions, as compared with that for patients with chronic ischemic heart disease in general. Signal-averaged ECGs have also been shown to predict arrhythmic events in patients with ischemic heart disease. In a subset of the ESVEM patients, antiarrhythmic drugs that block sodium channels were found to prolong the filtered, signal-averaged QRS duration, especially the late potential portion. This correlated with prolongation of the cycle length of induced ventricular tachycardia. Sotalol appeared to have a differential effect on the signal-averaged ECG; the signal-averaged QRS shortened slightly in patients in whom induction of VT was suppressed by sotalol, whereas it appeared to lengthen slightly in patients in whom VT remained inducible despite sotalol. This suggests that sotalol may affect conduction in diseased tissue in some patients, and that this may affect suppression of ventricular arrhythmia induction by programmed stimulation.

Endocardial fragmented electrogram and prediction of ventricular tachycardia by body surface signal-averaged electrocardiographic mapping

Signal-averaged (SA) electrocardiography and SA electrocardiographic mapping were performed in 50 patients with old myocardial infarction, 19 of whom had left ventricular aneurysm and 11 of whom had clinical sustained ventricular tachycardia. The SA electrocardiogram and SA electrocardiographic mapping data were then compared with those obtained by endocardial catheter mapping in patients with or without fragmented electrograms, sustained ventricular tachycardia, and ventricular aneurysm. Compared to SA electrocardiography, the SA map correlates with sustained VT with improved sensitivity but decreased specificity. However, SA electrocardiographic mapping had the advantage of displaying the extent of the body surface area that was positive for late potentials. In addition, the site of the longest endocardial fragmented electrogram could be predicted by SA electrocardiographic mapping, suggesting that this technique deserves wider clinical application.

Phase and group-delay characteristics of signal-averaged electrocardiograms from patients with ventricular tachycardia

Fourier analysis of the signal-averaged ECG (SAECG) has previously revealed significant differences in magnitude spectra that differentiate patients with ventricular tachycardia (VT) from those without VT. To determine additional distinguishing features in the frequency domain, we analyzed phase spectra of SAECG's of sinus beats from 57 patients with VT, 65 without VT, and 20 normal controls. Unwrapped phase spectra from SAECG's of the entire cardiac cycle were calculated with respect to three fiducial points: onset of the P and Q waves, and the negative of the slope of the phase (group delay) for frequencies in the band, which accounted for 97.5% of the energy in the vector magnitude of the Frank SAECG leads. Phase spectra of SAECG's from patients with VT differed from the non-VT patients at frequencies > or = 21 Hz (p = 0.000039) for the P-wave fiducial, at frequencies > or = 60 Hz (p = 0.00085) for the Q-wave fiducial, and at frequencies < or = 62 Hz (p = 0.0035) for the 97.5% energy fiducial. Group delays in SAECG's from patients with and without VT differed from 10 to 26 Hz (p = 0.000016) for the P-wave fiducial, and from 14 to 24 Hz (p = 0.00000070) for the Q-wave fiducial. Group delays with respect to the Q-wave fiducial in the VT patients in the 14-24 Hz band were, on average, 9 ms and 5 ms longer than those of the non-VT's and normals, respectively. Thus, phase spectra of SAECG's contain previously undetected features that together with magnitude may be helpful in improving methods for stratifying the risk of VT.

Correlation of the endocardial fragmented electrogram with body surface signal-averaged electrocardiographic mapping

We compared signal-averaged electrocardiography (SAE), SAE mapping, and left ventricular catheter mapping in 60 patients with ischemic heart disease. Using the data obtained in patients with no fragmented electrograms (FE) in the left ventricle, the late potential was defined by SAE as a filtered QRS duration > 131 msec or a root mean square voltage < 16 microV for the last 40 msec of the QRS complex. SAE mapping was performed by recording the signal-averaged electrocardiogram at 48 sites on the body surface. With SAE mapping, the filtered QRS duration and the area in the last 20 msec of the QRS complex were significantly different between the patients with and without FEs. The late potential was defined by SAE mapping as a filtered QRS duration > 136 msec or an area < 28 microV.msec for the last 20 msec of the QRS complex. The sensitivity and specificity of detecting FEs were 46% and 88%, respectively, by the SAE filtered QRS criterion, while they were 66% and 88% by the root mean square criterion. In contrast, SAE mapping gave values of 66% and 92% by the filtered QRS criterion, as well as values of 100% and 92% by the area criterion. Thus, SAE mapping provided better detection of the FE and was more closely correlated with the results of catheter mapping, suggesting its potential for clinical application.

Identifying the end of ventricular activation: body surface late potentials versus electrogram measurements in a canine infarction model

INTRODUCTION

Identification of the end of the QRS is perhaps the single most important feature obtained from the high resolution signal-averaged electrocardiogram (SAECG). This point relies on computer algorithms to select a point above the noise levels. Prior studies to substantiate this approach using electrograms for comparison have demonstrated many examples of the body surface recordings failing to detect the full extent of the late potentials.

METHODS AND RESULTS

An animal model that generates late potentials was used in conjunction with epicardial cardiac mapping system to systematically examine the reasons for these failures. In 11 of 13 dogs we found a concordance between the signal-averaged recordings and the epicardial recordings within 5 msec. The two discordant studies were attributed to a failure of epicardial mapping to record all late potential sources. Also, a means of accurately comparing measurements from the two recording technologies was required in this study as well as a new definition for identifying the end of activation currents in epicardial electrograms.

CONCLUSION

To achieve these results required approaches different from those used in the clinical setting to record the SAECG. These include: (1) the analysis of individual XYZ leads as opposed to the vector magnitude derived from these leads; (2) visual identification of very low level signals, as automatic algorithms often fail to detect low level signals; and (3) the use of finite impulse response digital filters instead of the bidirectional Butterworth filter.