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Thermal-electrical modeling for epicardial atrial radiofrequency ablation

Epicardial radiofrequency ablation is increasingly being used for intraoperative treatment of atrial fibrillation. However, the effect of different parameters on the lesion characteristics has not been sufficiently characterized. We used a finite element model to calculate the temperature distribution in the atrial tissue under different conditions during a constant voltage radiofrequency ablation. Our simulation results show that although in the case of a thin atrium the lesion was less deep for a thin atrium, it was easier to achieve transmurality. While considering a thinner atrium, the location of the hottest point of the lesion shifted from the electrode tip to epicardial surface. This effect was due to the convective cooling of the circulating blood inside the atrium. This convective cooling phenomenon has almost negligible effects for atria thicker than 3 mm. The variability of the cooling values has no significant effect on the lesion, even for thin atria (1-2 mm). Increasing the electrode insertion depth (ID) in the tissue produced larger lesions. However, for thinner atria (thickness <2 mm), this increase in the ID reduced the lesion width. It was also proved that the presence of a fat layer between the electrode and the atrial tissue decreased significantly the lesion dimensions.

What affects esophageal injury during radiofrequency ablation of the left atrium? An engineering study based on finite-element analysis

Recent studies on intraoperative radiofrequency ablation of atrial fibrillation have reported some cases of injury to the esophagus. The aim of this study was to perform computer simulations using a theoretical model in order to investigate the effect of different factors on the temperature distributions in the esophagus during ablation. A three-dimensional model was built to include an active electrode, atrial tissue, epicardial fat layer and a fragment of esophagus, aorta and lung, all linked by connective tissue. The finite-element method was used to calculate the temperature distribution during a procedure of constant-temperature ablation. The lesion geometry was assessed using a 50 degrees C isotherm. Our results show that the electrical power directly applied to the esophagus is insignificant and hence the esophageal injury is exclusively due to thermal conduction from the atrium. The esophageal lesion is mainly influenced by the thickness of connective tissue. Both the programmed target temperature of the electrode and the duration of the ablation also have a significant effect on the lesion in the esophagus. In contrast, the epicardial fat layer (0.9 mm thickness) did not show a significant influence. In conclusion, this theoretical model allows us to study the effect of different factors on the thermal injury in the esophagus during intraoperative radiofrequency ablation of atrial tissue.

A cooled intraesophageal balloon to prevent thermal injury during endocardial surgical radiofrequency ablation of the left atrium: a finite element study

Recent clinical studies on intraoperative monopolar radiofrequency ablation of atrial fibrillation have reported some cases of injury to the esophagus. The aim of this study was to perform computer simulations using three-dimensional finite element models in order to investigate the feasibility of a cooled intraesophageal balloon appropriately placed to prevent injury. The models included atrial tissue and a fragment of esophagus and lung linked by connective tissue. The lesion depth in the esophagus was assessed using a 50 degrees C isotherm and expressed as a percentage of thickness of the esophageal wall. The results are as follows: (1) chilling the esophagus by means of a cooled balloon placed in the lumen minimizes the lesion in the esophageal wall compared to the cases in which no balloon is used (a collapsed esophagus) and with a non-cooled balloon; (2) the temperature of the cooling fluid has a more significant effect on the minimization of the lesion than the rate of cooling (the thermal transfer coefficient for forced convection); and (3) pre-cooling periods previous to RF ablation do not represent a significant improvement. Finally, the results also suggest that the use of a cooled balloon could affect the transmurality of the atrial lesion, especially in the cases where the atrium is of considerable thickness.

Comparative study of methods for ventricular activity cancellation in atrial electrograms of atrial fibrillation

Atrial fibrillation is a very common cardiovascular disease in clinical practice. One relevant issue to understand its pathophysiological mechanisms is the analysis and interpretation of atrial electrograms (AEG). To study these signals properly, ventricular activity has to be removed from the AEG. In this work, a new application of independent component analysis (ICA) to the AEG is presented, where ventricular activity is removed from atrial epicardial recordings making use of only one reference lead. Therefore the technique is suitable when multi-lead recordings are unavailable as in atrial implantable cardioverter defibrilators. In addition to the proposed new methodology this work also presents the first comparative study, making use of unipolar epicardial AEGs, among the ICA-based technique, template matching and subtraction (TMS), and adaptive ventricular cancellation (AVC) on a database of 20 patients. A performance comparative analysis was carried out by evaluating epicardial atrial waveform similarity (S) and ventricular depolarization reduction (VDR) as a function of atrial rhythm regularity on a beat-by-beat basis. Results indicate that, when the epicardial atrial rhythm is quite organized, ICA is able to preserve the atrial waveform very precisely and better than the other methods (median S = 99.64% +/- 0.31% in contrast to 95.18% +/- 2.71% for TMS and 94.76% +/- 4.12% for AVC). Moreover, ventricular reduction is the best for ICA (median VDR = 6.32 +/- 4.41 dB in contrast to 4.98 +/- 4.48 dB for TMS and 4.12 +/- 2.72 dB for AVC). On the other hand, when the atrial activity is disorganized, TMS notably improves performance (S = 97.72% +/- 1.87%), but ICA still is the best in waveform preservation (S = 98.22% +/- 1.53%) whereas AVC remains similar (S = 93.74% +/- 4.38%). In conclusion, ICA can be considered as notably the best approach to reduce ventricular activity from unipolar atrial electrograms in organized atrial arrhythmias. On the other hand, both TMS and ICA give quite similar results when the atrial arrhythmia is disorganized.

Esophageal Temperature During Radiofrequency‐Catheter Ablation of Left Atrium: A Three‐Dimensional Computer Modeling Study

Introduction: There is current interest in finding a way to minimize thermal injury in the esophagus during radiofrequency‐catheter ablation of the left atrium. Despite the fact that the esophageal temperature is now being monitored during ablation, the influence of different anatomic and technical factors on the temperature rise remains unknown.

Assessment of non-invasive time and frequency atrial fibrillation organization markers with unipolar atrial electrograms.

The standard electrocardiogram (ECG) is the most common non-invasive way to study atrial fibrillation (AF). In this respect, previous works have shown that the surface lead V(1) reflects mainly the dominant atrial frequency (DAF) of the right atrium (RA), which has been widely used to study AF. In a similar way, AF organization and fibrillatory (f) wave amplitude are two recently proposed non-invasive AF markers. These markers need to be validated with invasive recordings in order to assess their capability to reliably reflect the internal fibrillatory activity dynamics. In this work, these two non-invasive metrics have been compared with similar measures recorded from two unipolar atrial electrograms (AEGs). For both ECG and AEG signals, AF organization has been computed by applying a nonlinear regularity index, such as sample entropy (SampEn), to the atrial activity (AA) and to its fundamental waveform, defined as the main atrial wave (MAW). The surface and epicardial f wave amplitude has been estimated through their mean power. Results obtained for 38 patients showed statistically significant correlations between the values measured from surface and invasive recordings, thus corroborating the usefulness of the aforesaid markers in the non-invasive study of AF. Precisely, for AF organization computed from the MAW, the correlation coefficients between surface and both AEGs were R = 0.926 (p < 0.001) and R = 0.932 (p < 0.001). For f wave amplitude, slightly lower significant relationships were noticed, the correlation coefficients being R = 0.765 (p < 0.001) and R = 0.842 (p < 0.001). These outcomes together with interesting linear relationships found among the parameters suggest that AF regularity estimated via SampEn and f wave amplitude can non-invasively characterize the epicardial activity related to AF.

Bipolar electrosurgery with long electrodes for RF coagulation of atrial tissue

We performed experiments on porcine atrial tissue fragments with a custom-built bipolar electrosurgical forceps fitted with long electrodes (20 mm) in order to create long and transmural lesions. Results show that impedance monitoring during heating and visual supervision of the lesion zone, are optimum parameters to control lesion evolution and avoid overheating in the tissue. Transmural lesions without charring were created with 15 watts of power during 10-15 seconds on initial impedances between 50-90 ohm.

Stroke after coronary artery bypass grafting: Preoperative predictive accuracies of CHADS2 and CHA2DS2VASc stroke risk stratification schemes

OBJECTIVE Neurologic events after coronary artery bypass grafting are an infrequent but devastating complication. This study analyzed the preoperative predictive abilities of the CHADS(2) and CHA(2)DS(2)VASc stroke scores in patients undergoing isolated coronary artery bypass grafting. METHODS Included in the study were 2910 patients who underwent isolated coronary artery bypass grafting during a 19-year period. CHADS(2) and CHA(2)DS(2)VASc scores were computed for all patients, and outcomes were evaluated in terms of perioperative stroke and compared with 2 specific models for predicting surgical coronary artery bypass grafting stroke (Northern New England Cardiovascular Disease Study Group and Multicenter Study of Perioperative Ischemia Research Group). Perioperative stroke discrimination was quantified by computing the area under the receiver operating characteristic curve. RESULTS Overall, 62 (2.1%) had perioperative strokes. Areas under the curve were 0.71 (95% confidence interval, 0.64-0.78) for CHADS(2), 0.72 (95% confidence interval, 0.65-0.79) for CHA(2)DS(2)VASc, 0.69 (95% confidence interval, 0.61-0.76) for Northern New England Cardiovascular Disease Study Group, and 0.73 (95% confidence interval, 0.67-0.80) for Multicenter Study of Perioperative Ischemia Research Group scores. Northern New England Cardiovascular Disease Study Group and CHA(2)DS(2)VASc scores were better at discriminating patients with particularly low or high risk of stroke. CONCLUSIONS CHADS(2) and CHA(2)DS(2)VASc scores predicted perioperative coronary artery bypass grafting strokes with discriminatory abilities similar to those of specific predictive surgical coronary artery bypass grafting stroke models. All schemes tested showed similar limitations in discriminating patients with high postoperative stroke risk, with a high proportion being classified as having intermediate stroke risk.

Surgical ablation of permanent atrial fibrillation by means of maze radiofrequency: mid-term results.

Abstract  Background: The maze procedure can be performed surgically with radiofrequency, generating transmural ablation lines. We report our experience with a biatrial pattern of lesions based on the use of epicardial and endocardial radiofrequency ablation in an effort to minimize maze procedure. Method: In 85 patients undergoing cardiac surgery for established permanent atrial fibrillation (>3 months), a biauricular pattern of epicardic–endocardic maze lesions was performed. The main surgical procedures were diverse: 42 mitral valve surgeries, 7 mitrotricuspid valves, 18 mitroaortics, 4 mitroaortic and tricuspids, 2 aortic valves, 3 CABGs, 5 CABG and valve procedures, and 4 atrial septal defects. The mean age of the patients was 61 ± 12 (range 39–78). The mean duration of atrial fibrillation was 5.8 years (range 0.3 to 24). Results: Sixty‐two (72.9%) patients presented postoperative supraventricular arrhythmia. Hospital mortality was seen in five patients (5.8%). Two patients died after a 12‐month mean follow‐up (range 2 to 32). A total of 14.1% of patients remained with their previous atrial fibrillation and 85.9% recovered and maintained sinus rhythm, with two patients having a permanent pacemaker. A total of 56% patients have been followed‐up for a period of more than 6 months, and among them prevalence of sinus rhythm is 87.5%. Echocardiography detected biauricular contraction in 65% of them. After analyzing the data, factors involved in postoperative recurrence of atrial fibrillation after radiofrequency surgery were oldness of the atrial fibrillation (p < 0.01) and pre and postoperative left auricle volume (p < 0.04). Conclusion: Intraoperative radiofrequency has permitted us to perform the maze procedure in a simple way, with a low surgical morbid‐mortality. We have obtained an 85.9% electrographic effectiveness and a 65% recovery of atrial contraction. Postoperative incidence of arrhythmia is the main postoperative problem.

Noninvasive Time and Frequency Predictors of Long-Standing Atrial Fibrillation Early Recurrence after Electrical Cardioversion

Background:  Several clinical factors have been studied to predict atrial fibrillation (AF) recurrence after electrical cardioversion (ECV) with limited predictive value.