Termination of Atrial Fibrillation by Catheter Ablation Can Be Successfully Predicted from Baseline ECG

Termination of Atrial Fibrillation by Catheter Ablation Can Be Successfully Predicted from Baseline ECGButtu A.1, Van Zaen J.1, Viso A.1, Forclaz A.2, Pascale P.2, Narayan S.3, Vesin J.1, Pruvot E.21Applied Signal Processing Group, Swiss Federal Institute of Technology EPFL, Lausanne Switzerland2Department of Cardiology, University Hospital Center Vaudois CHUV, Lausanne Switzerland3University of California, San Diego - USACardiostim 2012IntroductionThe success rate of stepwise radiofrequency ablation (step-CA) for patients (pts) with long-standing persistent atrial fibrillation (LS-pAF) appears limited.

Multiple parameters have been used to predict the outcome of step-CA (AF cycle length AFCL, AF duration..).Limited success.

Aim of our study:To develop innovative indices from baseline ECG recordings (i.e. before ablation) that can predict the termination of AF during step-CA.

For patients with long-standing persistent atrial fibrillation, the success rate of stepwise radiofrequency ablation appears limited as the amount of ablation to achieve AF termination is unknown.Multiple parameters have been used to predict the outcome of stepwise catheter ablation (such as AF-duration) and also to monitor the effect of stepwise ablation such as the AF cycle length. However, with limited successTherefore, our study is aimed at developing innovative indices computed from the baseline ECG (during the procedure, before ablation) that can predict the termination of AFib during stepwse catheter ablation.2Methods17 consecutive male patients included. Clinical characteristics:Study populationAge (y)60 5AF duration (y)7 5Sustained AF (month)21 13BMI (kg/m2)30 6LVEF (%)48 11LA volume (ml)173 37Our study included 17 consecutive mal patients with the following characteristics.The mean age is 60 years old, they suffered from Afib since 7 years, and the mean time in sustained AFib before ablation was 21 months.3MethodsElectrophysiological study:Effective anticoagulation therapy for > 1 month.Antiarrhythmic drugs (except amiodarone and beta-blockers) were discontinued 5 half-lives before the procedure.General anesthesia.Catheter for mapping and ablation: 3.5 mm cooled-tip Navistar (Webster).Chest lead V6 was placed in the back (V6b), within the cardiac silhouette.

All patients had effective oral anticoagulation for more then 1 month.All antiarrhythmic drugs (except amiodarone and beta-blockers) were discontinued from more the 5 half-lives before the procedure which was performed under general anesthesia.Importantly, chest lead V6 was placed in the back (V6b), within the cardiac silhouette, to improve the recording of the antero-posterior activity of the atria.4MethodsAblation protocol:

Procedural end point:Termination of AF into sinus rhythm (SR) or atrial tachycardia (AT).Non terminated AF were cardioverted electrically.

Ablation started with the isolation of the pulmonary veins, followed by CFAEs ablation and left atrium linear ablation (roof and mitral isthmus). Then, if AF was not terminated, right atrium CFAEs and cavotricuspid isthmus ablation were also performed.5

MethodsSignal processing: adaptive harmonic frequency tracking

Power spectrum density

Dominant frequency?Time-frequency representation

Dominant frequencyFirst harmonicHow to extract the frequency content?Adaptive harmonic frequency tracking- The method applied on the pre-ablation ECG is called adaptive harmonic frequency tracking. Random signal generated with sinusoids and random noise similar to the fibrillatory waves of the ECG during Afib after QRST cancellation. If we look at its power spectrum density, it is difficult to tell where is the dominant frequency Because we dont look at the frequency content correctly. This panel shows you a time-frequency represensation showing on the x-axis the time and on the y-axis the instantaneous frequency.Note the variation over time of the instantaneous DF which explains the two peaks on the spectrum. As well as greater variations of its first harmonic, which explains the broadening at twice the DF.To overcome the limitation of analysis by blocks, we used an adaptive harmonic frequency tracking.6Methods

In this movie, the top plot shows the input signal, the middle plot the time-frequency representation and the bottom plot shows two filter with central frequencies corresponding to the instantaneous frequencies of the dominant of first harmonic respectively.The black line in the bottom plot illustrates the instantaneous spectrum. We can see that the dominant and first harmonic frequencies are moving over time and the filters correctly follow these variations, with a negligible adaptation delay.Note how accurate is the tracking over time of the DF fluctuations as shown in red as well as its first harmonic fluctuations in blue.7Methods Organization Measurements

Quantifies the cyclicity of the oscillations

Two organization measurements:Adaptive organization index (AOI): ratio between the power of the extracted components and the total power of the signal.Mean0.7 = Adaptive techniques allows us to extract the temporal signal corresponding to the dominant frequency in red and its first harmonic in blue. The first measure we can extract is the AOI defined as the ratio between the power of the dominant plus the first harmonic and the total power of the input signal.Example And by computing the mean of the AOI on given sequence, this index will quantify the cyclicity of the oscillations of the DF and its first harmonic. The closer to one, to more organized the signal will be. In this example, we have a mean AOI of 0.7, reflecting a well organized signal.8Methods Organization MeasurementsVariance of the phase difference (PD): variance of the slope of the phase difference.

Variance = 6.5 10-6Quantifies the regularity of the oscillations- The second measure we can derive, is based on the phase difference between the dominant and it first harmonic, which is shown in the middle plot. By computing the slope the phase difference, we assess of its variation. If the shape of oscillations doesnt change over time, the phase difference is linear and therefore its slope is constant. A change in the shape of the oscillations will translate into a change in the slope. Therefore the variance of the slope quantifies the regularity of the oscillations. The closer to zero, the higher the coupling between the dominant and its first harmonic.9MethodsAOI and PD were compared to classical indices:AFCL computed from the inverse of the dominant frequency (classical method) of chest leads V1 and V6b after QRST cancellation2.Organization index (OI)1: ratio of the power in a 1-Hz band centered on the dominant peak to the total power in the spectrum (FFT).

All the considered measures were computed from 10-sec ECG recordings at baseline, after QRST cancellation2.

1 Everett T. H. et al. IEEE J BME 2001; 48; 969-782 Lemay M. et al. IEE Trans Biomed Eng 2007; 54; 542-6

OI = 0.24In this study, these two adaptive indices were compared to classical ones:AFCL computed from the ECG by inversing the dominant frequency of all chest leads after QRST subtraction.The organization index (similar to the OI introduced by Everett) defined here as the ratio of the power in a 1-Hz band centered on the dominant peak. This panel shows you the peak DF and the frequency band used to compute the power. The OI is the ratio of the power in around the DF and its first hamonic (as shown in black), and the total power in blue. The OI here is equal to 0.24, typical for low organized signals.

All the considered measures were computed from 10-sec ECG recordings at baseline after QRST cancellation. It is essential to perform the QRST subtraction as a first step because it improves the reliability of AF analysis in ECG recordings.10ResultsStudy populationLeft terminated (LT = 11, 65%)Right terminated (RT = 2, 12%)Not terminated(NT = 4, 23%)Age (y)60 559 657 163 5AF duration (y)7 58 67 04 2Sustained AF (month)21 1317 811 2 39 11BMI (kg/m2)30 632 628 427 7LVEF (%)48 1144 1058 4 54 13LA volume (ml)173 37179 26178 87164 33Cumulative ablation time (min)55 1449 1163 2165 15 - Among the 17 patients, 11 were terminated during ablation within the left atrium (including PVI, CFAEs and linear ablation), 2 during right atrium ablation and 4 were not terminated and required electrical cardioversion. Among all the characteristics between the different three groups, it is interesting to note that only the mean duration of sustained AF was much larger for the NT group. The other characteristics were similar, including the left atrial volume.11Results

This panel shows you the various indices measured on lead V1 for the upper row, and on dorsal lead V6b for the lower row.AFCL computed on lead V1 was on average longer for left terminated patients, but with an important overlap with right terminated and non terminated patients, and no significance between the groups can be observed.The classical organization index showed a higher organization on V1 (with three outliers and a small overlap), but no difference could be observed on the dorsal lead V6b.Importantly AOI on V1 distinguished significantly LT patients (with no overlap, compared to OI). As previous studies have shown the V1 activity mostly correlates with activity from the right atrial appendage, our result suggests that patients where AF terminated during ablation within the left atrium had a higher organization into the RA appendage at baseline.Interestingly, the distribution of the PD was significantly different when measured on the dorsal lead V6b, showing a gradient of organization from LT, being the most organized one to RT which showed an intermediate pattern and NT which was the less organized. Interestingly, previous studies have shown that dorsal electrodes reflects activity from the LA. Our results suggest that LT patients also have a higher organization within the LA before ablation.12ConclusionsAdaptive algorithms based on the instantaneous tracking of the dominant frequency (and its harmonics) improve the assessment of organization during AF.

Our findings are suggestive of a higher baseline bi-atrial organization in LT patients.

Innovative adaptive indices appear as promising parameters to predict patients that can be left terminated.

Validation on a larger population is needed.Thank youVentricular activity cancellationImproves the reliability of ECG analysis during AF.Single-beat method2:QRS complexes and T-waves are treated separetly:QRS cancellation is an interpolation of atrial activity with weighted sinusoids.T-wave cancellation based on a dominant T-wave approach.Advantages: Independent of the length the ECG recording.No discontinuities and QRS residues in the resulting signals.2 Lemay M. et al. IEE Trans Biomed Eng 2007; 54; 542-6Ventricular activity cancellationExample (signal duration 10-sec, sampling frequency: 1kHz):

Chest lead V1SampleFrequency (Hz)Ventricular activity cancellationExample (signal duration 10-sec, sampling frequency: 1kHz):

Dorsal lead V6bSampleFrequency (Hz)Study presented at HRS 2012: Contribution of Left and Right Atrial Appendage Activities to ECG Fibrillation Waves.Methods:Clinical characteristics: prior to ablation, catheters (CAT) were introduced in 10 consecutive patients (605 y, continuous AF duration 2214 m):Quadripolar CAT in the RAA.Decapolar CAT in the coronary sinus (CS).Dudecapolar CAT in the LAA.10-sec epochs for a total duration of 270 sec were usedSignal processing:EGMs: automatic computation of AFCL from LAA, RAA and CS recordings.ECG: after QRST cancellation, computation of AFCL on all chest leads (V1 to V6b).Correlation: using Pearsons correlation coefficient, the correlation between AFCL was computed for each combination of chest leads and EGMs.ResultsRAA AFCL was best correlated with chest lead V1 (R = 0.96) and progressively dropped until V5 (R = 0.26).Interestingly, LAA AFCL showed the opposite pattern with the highest correlation in V6b (R = 0.95) and the lowest one in V2 (R = 0.26).

V1 reflects the activity from the RAA and the dorsal lead V6b reflects the LAA activityClinical resultsSites of AF termination for LT and RTLeft terminated (LT = 11, 65%)Right terminated (RT = 2, 12%)Left Atrium Roof2 LAA1 Coronary sinus2 Mitral isthmus6Right Atrium Cavotricuspid isthmus1 RAA1