Dominant Frequency Maps Research Articles

Is verapamil a double-edged sword in rate control of paroxysmal atrial fibrillation?

Over the last decade, remarkable progress has been made in the field of atrial fibrillation (AF) pathophysiology and management. There is no doubt that radiofrequency catheter ablation therapy improves the quality of life and left ventricular function in patients with symptomatic AF by improving the maintenance of sinus rhythm. 1 A new antiarrhythmic agent, dronedarone, was recently shown to reduce the composite outcome of cardiovascular hospitalization and death in patients with AF. 2 Moreover, novel approaches such as the dominant frequency (DF) analysis of atrial electrograms have offered clinicians a better insight into the pathogenesis of AF. 3 Despite these advancements, longterm maintenance of sinus rhythm is challenging, and persistent or permanent AF still develops in many patients. In these cases, control of the ventricular rate has an essential role in alleviating the symptoms and preventing the development of tachycardia-induced cardiomyopathy. Spectral analysis of atrial recordings increasingly has been used to detect areas with high atrial activation rate during AF. The main benefit of frequency domain analysis is that it can be applied to the complex electrograms of AF more easily than time domain measurements. 3 Experimental and clinical studies indicate that the DF sites within the pulmonary veins (PV) have an important role in the initiation and maintenance of paroxysmal AF. 4,5 Furthermore, it has been postulated that DF mapping can be used to guide rapid identification of extrapulmonary sites that drive AF. 6 In this issue, Kushiyama et al 7 report the results of a study that evaluated the effects of verapamil on regional distribution of DFs in the PVs and atria in 43 patients undergoing catheter ablation of paroxysmal AF. They found that the highest DF was localized in the PVs and showed that there was a substantial PV-to-atria DF gradient at baseline. These findings are in agreement with previous studies indicating that the PVs are the main drivers of paroxysmal AF. 4,5 It is well established that beta-blockers, calcium channel antagonists, and digitalis slow ventricular rate, but much fewer data are available on their effect on atrial arrhythmogenesis. Verapamil is a nondihydropyridine calcium channel antagonist with potent negative chronodropic and dromodropic effects. Due to its use-dependent dromodropic action, verapamil is highly effective in controlling rapid ventricular rate in AF, but has less effect on atrioventricular (AV) nodal conduction at a normal rate. Kushiyama et al 7 showed that verapamil caused variable changes in the PV excitation. The maximum PV DF increased in 65% of the patients and decreased in the remaining 35%. In contrast, verapamil consistently increased the DFs in all of the atrial recording sites. As a result of these tissue-specific effects, verapamil eliminated the PV-to-atria DF gradient. According to the investigators, this is attributable to regional heterogeneities of action potential morphology and ionic currents responsible for the repolarization (e.g., I CaL ) in the PV myocardial muscle sleeves and atria rather than to a reflex increase in sympathetic tone in response to a reduction in blood pressure. Prior studies indicate that the extrapulmonary DF areas and the absence of the PV-to-atria frequency gradient can be used to identify additional ablation targets. For example, Lin et al 6 have shown that the DF shifts to the right atrium when AF is initiated in the superior vena cava. Sanders et al 5 reported that termination of permanent AF requires ablation of extrapulmonary high-frequency sites in addition to PV isolation. Hence, it is tempting to speculate that ablation of the verapamil-induced atrial high-frequency areas may improve the long-term efficacy of catheter ablation of paroxysmal AF. The results of Kushiyama et al 7 are also important with regard to rate control of AF because they raise the possibility that verapamil may provoke paroxysmal AF by creating new high-frequency sources in the atria. In keeping with this, verapamil facilitated the induction of sustained AF. That is, in all of the 6 patients with no inducible AF at baseline, sustained AF was easily induced after verapamil by burst pacing from the coronary sinus. These findings are consistent with experimental data indicating that verapamil promotes maintenance of AF by shortening the atrial refractory period and AF cycle length and enhancing reentrant activity in the atria. 8 In lieu of these data, the usefulness of verapamil for ventricular rate control in patients with paroxysmal AF may be limited by its profibrillatory effect in

Letter by Berenfeld and Jalife Regarding Article “Dominant Frequency of Atrial Fibrillation Correlates Poorly With Atrial Fibrillation Cycle Length”

To the Editor: We read with interest the recent article by Elvan et al in Circulation: Arrhythmia and Electrophysiology .1 They compared the reliability of time-domain versus frequency-domain methods in determining the local activation rate in patients during atrial fibrillation (AF).2 The study provided potentially important information regarding the analysis of unipolar versus bipolar recordings. Unfortunately, essential details regarding the methods used for both the time-domain and the frequency-domain analyses were not presented. For example, information on the noise and frequency rejection criteria used for determination of AF cycle length in the time domain was nowhere to be found. Also crucial information on the …

The temporal variability of dominant frequency and complex fractionated atrial electrograms constrains the validity of sequential mapping in human atrial fibrillation

It has been proposed that sequential mapping of dominant frequency (DF) and complex fractionated atrial electrograms (CFAE) can identify target sites for ablation of atrial fibrillation (AF). These mapping strategies are valid only if DF and CFAE are temporally stable on the timescale of the mapping procedure. We postulate that DF and CFAE are temporally variable; consequently, sequential mapping can be misleading. To make prolonged spatially stable multielectrode recordings to assess the temporal stability of DF and CFAE. We recorded electrical activity for 5 minutes with the use of a 64-electrode basket catheter placed in the left atrium of 18 patients presenting for AF ablation. DF and CFAE were determined off-line, and their temporal variability was quantified. Maps created from simultaneous versus sequentially acquired data were compared. DF was temporally variable: the average temporal coefficient of variation was 22.7% +/- 5.4%. DF sites were transient, meeting criteria for only 22.1 seconds out of 5 minutes. Similarly, CFAEs were transient (average duration of CFAE 8.8 +/- 11.3 seconds). DF and CFAE sequential maps failed to identify 93.0% +/- 12.4% and 35.9% +/- 14.9% of DF and CFAE sites, respectively. Because of temporal variability, sequential DF and CFAE maps do not accurately reflect the spatial distribution of excitation frequency during any given sampling interval. The spatial distribution of DF and CFAE sites on maps created with sequential point acquisition depends upon the time at which each site is sampled.

Dominant Frequency Mapping of Atrial Fibrillation: Comparison of Contact and Noncontact Approaches

The ability to acquire a dominant frequency (DF) map during atrial fibrillation (AF) instantaneously using noncontact mapping has significant advantages over the current sequential contact mapping approach; however, the relationship between DFs determined from contact bipolar and noncontact unipolar recordings is unknown. We sought to determine the difference between DFs determined using contact bipolar, contact unipolar, noncontact unipolar, and noncontact pseudobipolar recordings. Sustained AF was induced in 5 canines with 10 weeks of atrial tachy-pacing at 440 ppm. A noncontact multielectrode array was positioned in the left atrium (LA). Two simultaneous contact signals (unipolar and bipolar) and 3 noncontact signals (unipolar, pseudobipolar, and pseudobipolar Laplacian) were recorded from multiple LA sites. Fourier analysis was performed, and the DFs of contact and noncontact signals were compared. Recordings were obtained from 389 LA locations in 5 canines. The correlation was best between contact bipolar and noncontact QRS-subtracted unipolar signals (r = 0.58, P < 0.001), and weaker between contact bipolar and noncontact best-fit pseudobipolar (r = 0.50, P < 0.01) and noncontact Laplacian bipolar (r = 0.49, P < 0.01). There was no significant difference in the mean DFs between contact bipolar and noncontact unipolar signals; however, there was a significant difference in the DFs comparing contact bipolar to noncontact pseudobipolar signals (11.6 +/- 1.8 vs 11.2 +/- 2.5 Hz; P = 0.004) and a small nonsignificant difference comparing contact bipolar DF and noncontact pseudobipolar Laplacian DF (11.4 +/- 1.8 vs 11.1 +/- 1.6 Hz; P = NS). We found that estimation of DFs using noncontact mapping is feasible and that QRS-subtracted noncontact unipolar signals perform better than noncontact pseudobipolar signals at estimating contact bipolar DFs. This has important implications for developing algorithms for noncontact frequency mapping of AF.

Real-time dominant frequency mapping and ablation of dominant frequency sites in atrial fibrillation with left-to-right frequency gradients predicts long-term maintenance of sinus rhythm

Spectral analysis identifies localized sites of high-frequency activity during atrial fibrillation (AF). This study sought to determine the effectiveness of using real-time dominant frequency (DF) mapping for radiofrequency ablation of maximal DF (DFmax) sites and elimination of left-to-right frequency gradients in the long-term maintenance of sinus rhythm (SR) in AF patients. DF mapping was performed in 50 patients during ongoing AF (32 paroxysmal, 18 persistent), acquiring a mean of 117 +/- 38 points. Ablation was performed targeting DFmax sites, followed by circumferential pulmonary vein isolation. Ablation significantly reduced DFs (Hz) in the LA (7.9 +/- 1.4 vs. 5.7 +/- 1.3, P <.001), coronary sinus (CS) (5.7 +/- 1.1 vs. 5.3 +/- 1.2, P = .006), and RA (6.3 +/- 1.4 vs. 5.4 +/- 1.3, P <.001) abolishing baseline left-to-right atrial DF gradient (1.7 +/- 1.7 vs. 0.2 +/- 0.9; P <.001). Only a significant reduction in DFs in all chambers with a loss of the left-to-right atrial gradient after ablation was associated with a higher probability of long-term SR maintenance in both paroxysmal and persistent AF patients. After a mean follow-up of 9.3 +/- 5.4 months, 88% of paroxysmal and 56% of persistent AF patients were free of AF (P = .02). Ablation of DFmax sites was associated with a higher probability of remaining both free of arrhythmias (78% vs. 20%; P = .001) and free of AF (88% vs. 30%; P <.001). Radiofrequency ablation leading to elimination of LA-to-RA frequency gradients predicts long-term SR maintenance in AF patients.

Spatial-temporal filter effect in a computer model study of ventricular fibrillation / Räumlicher und zeitlicher Filtereffekt in einer Computermodellstudie zum Herzkammerflimmern

Prediction of countershock success from ventricular fibrillation (VF) ECG is a major challenge in critical care medicine. Recent findings indicate that stable, high frequency mother rotors are one possible mechanism maintaining VF. A computer model study was performed to investigate how epicardiac sources are reflected in the ECG. In the cardiac tissues of two computer models - a model with cubic geometry and a simplified torso model with a left ventricle - a mother rotor was induced by increasing the potassium rectifier current. On the epicardium, the dominant frequency (DF) map revealed a constant DF of 23 Hz (cubic model) and 24.4 Hz (torso model) in the region of the mother rotor, respectively. A sharp drop of frequency (3-18 Hz in the cubic model and 12.4-18 Hz in the torso model) occurred in the surrounding epicardial tissue of chaotic fibrillatory conduction. While no organized pattern was observable on the body surface of the cubic model, the mother rotor frequency can be identified in the anterior surface of the torso model because of the chosen position of the mother rotor in the ventricle (shortest distance to the body surface). Nevertheless, the DFs were damped on the body surfaces of both models (4.6-8.5 Hz in the cubic model and 14.4-16.4 Hz in the torso model). Thus, it was shown in this computer model study that wave propagation transforms the spatial low pass filtering of the thorax into a temporal low pass. In contrast to the resistive-capacitive low pass filter formed by the tissue, this spatial-temporal low pass filter becomes effective at low frequencies (tens of Hertz). This effect damps the high frequency components arising from the heart and it hampers a direct observation of rapid, organized sources of VF in the ECGs, when in an emergency case an artifact-free recording is not possible.

Activation of Inward Rectifier Potassium Channels Accelerates Atrial Fibrillation in Humans

It is unclear whether atrial fibrillation (AF) drivers in humans are focal or reentrant. To test the hypothesis that functional reentry is involved in human AF maintenance, we determined the effects of adenosine infusion on local dominant frequency (DF) at different atrial sites. By increasing inward rectifier potassium channel conductance, adenosine would increase DF of reentrant drivers but decrease it in the case of a focal mechanism. Thirty-three patients were studied during AF (21 paroxysmal, 12 persistent) using recordings from each pulmonary vein-left atrial junction (PV-LAJ), high right atrium, and coronary sinus. DFs were determined during baseline and peak adenosine effect. In paroxysmal AF, adenosine increased maximal DF at each region compared with baseline (PV-LAJ, 8.03+/-2.2 versus 5.7+/-0.8; high right atrium, 7+/-2.2 versus 5.4+/-0.7; coronary sinus, 6.6+/-1.1 versus 5.3+/-0.7 Hz; P=0.001) and increased the left-to-right DF gradient (P=0.007). In contrast, in persistent AF, adenosine increased DF only in the high right atrium (8.33+/-1.1 versus 6.8+/-1.2 Hz; P=0.004). In 4 paroxysmal AF patients, real-time DF mapping of the left atrium identified the highest DF sites near the PV-LAJ, where adenosine induced an increase in DF (6.7+/-0.29 versus 4.96+/-0.26 Hz; P=0.008). Finally, simulations demonstrate that the frequency of reentrant drivers accelerates proportionally to the adenosine-modulated inward rectifier potassium current. Adenosine accelerates drivers and increases frequency differently in paroxysmal compared with persistent human AF. The results strongly suggest that AF is maintained by reentrant sources, most likely located at the PV-LAJ in paroxysmal AF, whereas non-PV locations are more likely in persistent AF.

Abstract 191: Analysis Of Conduction Block During Ventricular Fibrillation In Langendorff Perfused Explanted Human Hearts.

Purpose Rotors in Ventricular Fibrillation (VF) are known to occur in distinct domains identified by dominant frequency (DF). It has been postulated that VF is driven by these domains of excitation with fibrillatory propagation to adjacent domains with conduction blocks. If the dominant domain hypothesis is applicable to human VF, we postulated that minimally during VF, areas blocks in a DF map should localize at boundaries of DF domains. Methods Explanted hearts from 4 patients undergoing cardiac transplant were perfused with Krebs-Henseilet solution. The epicardial and endocardial mapping was constructed with 112 electrodes disposed on an extensible sock and balloon array. The electrodes were organized in 14 rows of 8 electrodes disposed radially around the apex. 12 episodes of VF from the 4 hearts were analyzed. Fast Fourier Transformation (FFT) analysis was performed with a resolution of 0.25 Hz. DF domain was defined as a region on the DF map with uniform DF. Double peak (DP) an estimate of conduction block, was identified at a time point if a secondary peak was present in the power spectrum of an FFT that was within a maximum separation of 80% of the dominant (highest) peak frequency and that had an amplitude of at least 20% of the amplitude of the dominant peak. Results The average DF was 4.64±1.20 Hz. The mean percentage of blocks was 26.13±12.19 %. The average number of domains per DF map were 9.25±3.77. The mean percent block per domain was 2.95±1.27.The number of domains per map correlated significantly to areas with blocks. (r = 0.49, p=0.014). When the hearts were individually analyzed, the correlation was greater than when analyzed together. Higher occurrence of block is seen with increasing number of DF domains. Conclusions During human VF, areas of blocks in a DF map localize at boundaries of DF domains.

Spectral Analysis Identifies Sites of High-Frequency Activity Maintaining Atrial Fibrillation in Humans

Background— The identification of sites of dominant activation frequency during atrial fibrillation (AF) in humans and the effect of ablation at these sites have not been reported. Methods and Results— Thirty-two patients undergoing AF ablation (19 paroxysmal, 13 permanent) during ongoing arrhythmia were studied. Electroanatomic mapping was performed, acquiring 126±13 points per patient throughout both atria and coronary sinus. At each point, 5-second electrograms were obtained to determine the highest-amplitude frequency on spectral analysis and to construct 3D dominant frequency (DF) maps. The temporal stability of the recording interval was confirmed in a subset. Ablation was performed with the operator blinded to the DF maps. The effect of ablation at sites with or without high-frequency DF sites (maximal frequencies surrounded by a decreasing frequency gradient ≥20%) was evaluated by determining the change in AF cycle length (AFCL) and the termination and inducibility of AF. The spatial distribution ...

Discovery of gradient pattern in dominant frequency maps during fibrillation: implication of rotor drift and epicardial conduction velocity changes

Dominant frequency (DF) maps for mapping epicardial activations of ventricular fibrillation (VF) have been studied mainly using fast Fourier transform (FFT). Small and discrete DF domains exhibited in these DF maps have undermined the hypothesis of mother rotor for VF maintenance. We applied continuous Fourier transform (CFT) to generate high-precision DF maps and studied characteristics of these high-precision DF maps. Optical epicardial activations were recorded in isolated rabbit hearts (n = 10). Continuous Fourier transform of 1-second segments was performed in VF (n = 188) and ventricular tachycardia (n = 189) at 0.1 Hz precisions. Banded gradient patterns of gradual change in DF values were observed in 136 of 188 VF segments, but not in ventricular tachycardia. These gradients were not observed when FFT was used. Gradients were observed along the conduction path of reentrant-like waves with decreasing DF values along the path. Spectra in the gradients did not exhibit bimodal spectra as is usually observed in traditional DF domain boundaries. Time-space plots revealed clear association between gradient pattern and epicardial conduction velocity changes. Prior simulation studies predicted a gradient in activation rate during rotor drift. This gradient pattern has been observed for the first time experimentally by only using CFT, but not FFT. High-precision DF videos indicated the existence of gradient movement from one spatial location to another, smoothly instead of randomly disappearing from one location and appearing in another. The discovery of associated pseudoconduction velocity changes, and gradient patterns might suggest that dominant rotor (mother rotor) drifting plays a maintenance role only detectable by CFT and not FFT.

3D configuration of Mygdonian basin and preliminary estimate of its site response

Euroseistest is currently the longest running test site in the world. It was originally defined as the 2D cross-section of the Mygdonian basin going from Profitis to Stivos villages. In this paper, we present the first results of the effort to extend the idea of test site to a larger portion of the whole sedimentary structure, i.e. the extension of the idea of Euroseistest from a 2D to a 3D structure. To this end we have compiled available geological and geotechnical information. We have analyzed microtremor and earthquake data recorded seven years ago, that had not been thoroughly exploited. We present the results of the analysis of H/V spectral ratios from microtremors recorded at 195 sites, and from earthquake records at 14 stations. The results are validated through comparison with the well studied 2D cross-section. In addition to this, the geometry of the edges of the basin has been deduced from electrical tomographies. The synthesis of all these data allowed us to propose reliable map of dominant frequencies throughout the basin, a good constrain on the geometry of the basin at the edges, and shear-wave velocity profiles at some points. Our results indicate that average shear-wave velocity is not constant throughout, and thus the dominant frequency map is not a faithful image of the geometry of the basin. We have also obtained a reliable estimate of the site response throughout the basin. The results have been used to plan an additional measurement campaign, and are currently used to compute site response using a 3D seismic modelling code. We expect that the usefulness of Euroseistest to understand site effects in 3D geological structures will be as large as it has been in its 2D phase.

Spectral Analysis Identifies Sites of High-Frequency Activity Maintaining Atrial Fibrillation in Humans

The identification of sites of dominant activation frequency during atrial fibrillation (AF) in humans and the effect of ablation at these sites have not been reported. Thirty-two patients undergoing AF ablation (19 paroxysmal, 13 permanent) during ongoing arrhythmia were studied. Electroanatomic mapping was performed, acquiring 126+/-13 points per patient throughout both atria and coronary sinus. At each point, 5-second electrograms were obtained to determine the highest-amplitude frequency on spectral analysis and to construct 3D dominant frequency (DF) maps. The temporal stability of the recording interval was confirmed in a subset. Ablation was performed with the operator blinded to the DF maps. The effect of ablation at sites with or without high-frequency DF sites (maximal frequencies surrounded by a decreasing frequency gradient > or =20%) was evaluated by determining the change in AF cycle length (AFCL) and the termination and inducibility of AF. The spatial distribution of the DF sites was different in patients with paroxysmal and permanent AF; paroxysmal AF patients were more likely to harbor the DF site within the pulmonary vein, whereas in permanent AF, atrial DF sites were more prevalent. Ablation at a DF site resulted in significant prolongation of the AFCL (180+/-30 to 198+/-40 ms; P<0.0001; kappa=0.77), whereas in the absence of a DF site, there was no change in AFCL (169+/-22 to 170+/-22 ms; P=0.4). AF terminated during ablation in 17 of 19 patients with paroxysmal and 0 of 13 with permanent AF (P<0.0001). When 2 patients with nonsustained AF during mapping were excluded, 13 of 15 (87%) had AF termination at DF sites (54% at the initially ablated DF site): 11 pulmonary veins and 2 atrial. In addition, AF could no longer be induced in 69% with termination of AF at a DF site. There were no significant differences in the number or percentage of DF sites detected (5.4+/-1.6 versus 4.9+/-2.1; P=0.3) and ablated (1.9+/-1.0 versus 2.4+/-1.0; P=0.3) in those with and without AF termination. The duration of radiofrequency ablation to achieve termination was significantly shorter than that delivered in those with persisting AF (34.8+/-24.0 versus 73.5+/-22.9 minutes; P=0.0002). All patients with persisting AF had additional DF sites outside the ablated zones. Spectral analysis and frequency mapping identify localized sites of high-frequency activity during AF in humans with different distributions in paroxysmal and permanent AF. Ablation at these sites results in prolongation of the AFCL and termination of paroxysmal AF, indicating their role in the maintenance of AF.

Altered electroanatomic patterns of right ventricle in myotonic dystrophy type 1 patients

Background: Prolongation of the atrial fibrillation cycle length (AFCL) and termination of AF during ablation have been reported. We investigate the significance of regions of maximal dominant frequency (DF) identified by spectral analysis, determining the effect of ablation at these sites located within the pulmonary veins (PV) on the fibrillatory process. Methods: Thirty-two patients undergoing AF ablation during ongoing arrhythmia were studied. Electroanatomic mapping was performed, acquiring 126 13 points/pt throughout both atria and coronary sinus (CS). At each point, 5s electrograms were obtained to determine the highest amplitude frequency on spectral analysis and construct 3D DF maps. Ablation was performed with the operator blinded to the DF maps. The effect of ablation at PVs with or without high-frequency DF sites (maximal frequencies surrounded by a decreasing frequency gradient 20%) was evaluated by determining the change in AFCL within the CS before and after isolation of each PV, and the termination of AF. Results: PV ablation was associated with an increase in AFCL (174 27 to 184 35ms; p 0.0001). While ablation at a PV harboring a DF site resulted in AFCL prolongation (180 30 to 198 40ms; p 0.0001), ablation at a PV without a DF site did not change the AFCL (169 22 to 170 22ms; p 0.4). Ablation at PVs harboring a DF site resulted in an increase in AFCL ( 5ms) within the CS in 89% with the mean increase in AFCL of 18 21ms (range 0-118ms) compared to 0.9 3.9ms (range -10 to 7ms; p 0.0001) after ablation at PVs without a DF site. The increase in AFCL with PV ablation demonstrated a strong concordance with ablation at a DF site (kappa-coefficient of 0.77). PV ablation resulted in AF termination in 14 pts; 11 at a DF site. In the remaining 3, 2 had frequent cessation of arrhythmia during mapping. Conclusion: High frequency PV activity identified by spectral analysis has an important role in maintaining AF. Ablation at these sites resulted in slowing of the fibrillatory process and termination of paroxysmal AF.

Wavebreak formation during ventricular fibrillation in the isolated, regionally ischemic pig heart.

Both fixed and dynamic heterogeneities were implicated in the mechanism of wavebreak (WB) generation during ventricular fibrillation (VF). However, their relative roles remain unclear. We hypothesized that during ischemic VF, the WBs are produced primarily because of a fixed heterogeneity; namely, the gradient of refractoriness across the ischemic border zone (BZ). Ischemia was induced in 15 isolated blood-perfused hearts by occluding the left anterior descending coronary artery. Simultaneous video imaging (approximately 32x32 mm2) of Di-4-ANEPPS fluorescence in the ischemic zone (IZ), the BZ, and the nonischemic zone (NIZ) was performed. Dominant-frequency maps were constructed to assess gradients of refractoriness during VF. We used singularity points analysis to quantify the incidence of WBs per square centimeter per second. During preischemic VF, the distribution of WBs was relatively uniform. Ischemia caused an increase of WBs in the BZ (from 6.2+/-2.8 to 10.8+/-4.0) and a decrease of WBs in the IZ (from 5.8+/-2.8 to 2.8+/-1.4), without a significant change in NIZ (from 6.4+/-2.3 to 4.1+/-1.7). This finding is fully consistent with the dominant-frequency distribution during ischemic VF: the average dominant frequency was significantly slower in IZ than in NIZ (7.8+/-0.7 versus 10.1+/-1.0 Hz), suggesting a large gradient in refractory periods across the BZ. We concluded that acute regional ischemia plays a dual role in the maintenance of VF, decreasing the incidence of WB in the IZ while increasing it in the BZ. This suggests a predominant role of fixed heterogeneities in the formation of WB during VF in acute regional ischemia.

Distribution of Excitation Frequencies on the Epicardial and Endocardial Surfaces of Fibrillating Ventricular Wall of the Sheep Heart

Tissue heterogeneities may play an important role in the mechanism of ventricular tachycardia (VT) and fibrillation (VF) and can lead to a complex spatial distribution of excitation frequencies. Here we used optical mapping and Fourier analysis to determine the distribution of excitation frequencies in >20 000 sites of fibrillating ventricular tissue. Our objective was to use such a distribution as a tool to quantify the degree of organization during VF. Fourteen episodes of VT/VF were induced via rapid pacing in 9 isolated, coronary perfused, and superfused sheep ventricular slabs (3x3 cm(2)). A dual-camera video-imaging system was used for simultaneous optical recordings from the entire epi- and endocardial surfaces. The local frequencies of excitation were determined at each pixel and displayed as dominant frequency (DF) maps. A typical DF map consisted of several (8.2+/-3.6) discrete areas (domains) with a uniform DF within each domain. The DFs in adjacent domains were often in 1:2, 3:4, or 4:5 ratios, which was shown to be a result of an intermittent Wenckebach-like conduction block at the domain boundaries. The domain patterns were relatively stable and could persist from several seconds to several minutes. The complexity in the organization of the domains, the number of domains, and the dispersion of frequencies increased with the rate of the arrhythmia. Domain patterns on the epicardial and endocardial surfaces were not correlated. Sustained epicardial or endocardial reentry was observed in only 3 episodes. Observed frequency patterns during VT/VF suggest that the underlying mechanism may be a sustained intramural reentrant source interacting with tissue heterogeneities.