Evaluation of functional warm ischemia time during controlled donation after circulatory determination of death using normothermic regional perfusion (ECMO-TT): A prospective multicenter cohort study.

BACKGROUND: Controlled donation after circulatory determination of death (cDCD) seems an effective way to mitigate the critical shortage of available organs for transplant worldwide. As a recently developed procedure for organ retrieval, some questions remain unsolved such as the uncertainty regarding the effect of functional warm ischemia time (FWIT) on organs´ viability. METHODS: We developed a multicenter prospective cohort study collecting all data from evaluated organs during cDCD from 2017 to 2020. All the procedures related to cDCD were performed with normothermic regional perfusion. The analysis included organ retrieval as endpoint and FWIT as exposure of interest. The effect of FWIT on the likelihood for organ retrieval was evaluated with Relative distribution analysis. RESULTS: A total amount of 507 organs´ related information was analyzed from 95 organ donors. Median donor age was 62 years, and 63% of donors were male. Stroke was the most common diagnosis before withdrawal of life-sustaining therapy (61%), followed by anoxic encephalopathy (21%). This analysis showed that length of FWIT was inversely associated with organ retrieval rates for liver, kidneys, and pancreas. No statistically significant association was found for lungs. CONCLUSIONS: Results showed an inverse association between functional warm ischemia time (FWIT) and retrieval rate. We also have postulated optimal FWIT's thresholds for organ retrieval. FWIT for liver retrieval remained between 6 and less than 11 min and in case of kidneys and pancreas, the optimal FWIT for retrieval was 6 to 12 min. These results could be valuable to improve organ utilization and for future analysis.

A Novel Signal Restoration Method of Noisy Photoplethysmograms for Uninterrupted Health Monitoring.

Health-tracking from photoplethysmography (PPG) signals is significantly hindered by motion artifacts (MAs). Although many algorithms exist to detect MAs, the corrupted signal often remains unexploited. This work introduces a novel method able to reconstruct noisy PPGs and facilitate uninterrupted health monitoring. The algorithm starts with spectral-based MA detection, followed by signal reconstruction by using the morphological and heart-rate variability information from the clean segments adjacent to noise. The algorithm was tested on (a) 30 noisy PPGs of a maximum 20 s noise duration and (b) 28 originally clean PPGs, after noise addition (2-120 s) (1) with and (2) without cancellation of the corresponding clean segment. Sampling frequency was 250 Hz after resampling. Noise detection was evaluated by means of accuracy, sensitivity, and specificity. For the evaluation of signal reconstruction, the heart-rate (HR) was compared via Pearson correlation (PC) and absolute error (a) between ECGs and reconstructed PPGs and (b) between original and reconstructed PPGs. Bland-Altman (BA) analysis for the differences in HR estimation on original and reconstructed segments of (b) was also performed. Noise detection accuracy was 90.91% for (a) and 99.38-100% for (b). For the PPG reconstruction, HR showed 99.31% correlation in (a) and >90% for all noise lengths in (b). Mean absolute error was 1.59 bpm for (a) and 1.26-1.82 bpm for (b). BA analysis indicated that, in most cases, 90% or more of the recordings fall within the confidence interval, regardless of the noise length. Optimal performance is achieved even for signals of noise up to 2 min, allowing for the utilization and further analysis of recordings that would otherwise be discarded. Thereby, the algorithm can be implemented in monitoring devices, assisting in uninterrupted health-tracking.

Novel Entropy-Based Metrics for Long-Term Atrial Fibrillation Recurrence Prediction Following Surgical Ablation: Insights from Preoperative Electrocardiographic Analysis.

Atrial fibrillation (AF) is a prevalent cardiac arrhythmia often treated concomitantly with other cardiac interventions through the Cox-Maze procedure. This highly invasive intervention is still linked to a long-term recurrence rate of approximately 35% in permanent AF patients. The aim of this study is to preoperatively predict long-term AF recurrence post-surgery through the analysis of atrial activity (AA) organization from non-invasive electrocardiographic (ECG) recordings. A dataset comprising ECGs from 53 patients with permanent AF who had undergone Cox-Maze concomitant surgery was analyzed. The AA was extracted from the lead V1 of these recordings and then characterized using novel predictors, such as the mean and standard deviation of the relative wavelet energy (RWEm and RWEs) across different scales, and an entropy-based metric that computes the stationary wavelet entropy variability (SWEnV). The individual predictors exhibited limited predictive capabilities to anticipate the outcome of the procedure, with the SWEnV yielding a classification accuracy (Acc) of 68.07%. However, the assessment of the RWEs for the seventh scale (RWEs7), which encompassed frequencies associated with the AA, stood out as the most promising individual predictor, with sensitivity (Se) and specificity (Sp) values of 80.83% and 67.09%, respectively, and an Acc of almost 75%. Diverse multivariate decision tree-based models were constructed for prediction, giving priority to simplicity in the interpretation of the forecasting methodology. In fact, the combination of the SWEnV and RWEs7 consistently outperformed the individual predictors and excelled in predicting post-surgery outcomes one year after the Cox-Maze procedure, with Se, Sp, and Acc values of approximately 80%, thus surpassing the results of previous studies based on anatomical predictors associated with atrial function or clinical data. These findings emphasize the crucial role of preoperative patient-specific ECG signal analysis in tailoring post-surgical care, enhancing clinical decision making, and improving long-term clinical outcomes.

An Efficient Hybrid Methodology for Local Activation Waves Detection under Complex Fractionated Atrial Electrograms of Atrial Fibrillation.

Local activation waves (LAWs) detection in complex fractionated atrial electrograms (CFAEs) during catheter ablation (CA) of atrial fibrillation (AF), the commonest cardiac arrhythmia, is a complicated task due to their extreme variability and heterogeneity in amplitude and morphology. There are few published works on reliable LAWs detectors, which are efficient for regular or low fractionated bipolar electrograms (EGMs) but lack satisfactory results when CFAEs are analyzed. The aim of the present work is the development of a novel optimized method for LAWs detection in CFAEs in order to assist cardiac mapping and catheter ablation (CA) guidance. The database consists of 119 bipolar EGMs classified by AF types according to Wells' classification. The proposed method introduces an alternative Botteron's preprocessing technique targeting the slow and small-ampitude activations. The lower band-pass filter cut-off frequency is modified to 20 Hz, and a hyperbolic tangent function is applied over CFAEs. Detection is firstly performed through an amplitude-based threshold and an escalating cycle-length (CL) analysis. Activation time is calculated at each LAW's barycenter. Analysis is applied in five-second overlapping segments. LAWs were manually annotated by two experts and compared with algorithm-annotated LAWs. AF types I and II showed 100% accuracy and sensitivity. AF type III showed 92.77% accuracy and 95.30% sensitivity. The results of this study highlight the efficiency of the developed method in precisely detecting LAWs in CFAEs. Hence, it could be implemented on real-time mapping devices and used during CA, providing robust detection results regardless of the fractionation degree of the analyzed recordings.

Practical Considerations for the Application of Nonlinear Indices Characterizing the Atrial Substrate in Atrial Fibrillation.

Atrial fibrillation (AF) is the most common cardiac arrhythmia, and in response to increasing clinical demand, a variety of signals and indices have been utilized for its analysis, which include complex fractionated atrial electrograms (CFAEs). New methodologies have been developed to characterize the atrial substrate, along with straightforward classification models to discriminate between paroxysmal and persistent AF (ParAF vs. PerAF). Yet, most previous works have missed the mark for the assessment of CFAE signal quality, as well as for studying their stability over time and between different recording locations. As a consequence, an atrial substrate assessment may be unreliable or inaccurate. The objectives of this work are, on the one hand, to make use of a reduced set of nonlinear indices that have been applied to CFAEs recorded from ParAF and PerAF patients to assess intra-recording and intra-patient stability and, on the other hand, to generate a simple classification model to discriminate between them. The dominant frequency (DF), AF cycle length, sample entropy (SE), and determinism (DET) of the Recurrence Quantification Analysis are the analyzed indices, along with the coefficient of variation (CV) which is utilized to indicate the corresponding alterations. The analysis of the intra-recording stability revealed that discarding noisy or artifacted CFAE segments provoked a significant variation in the CV(%) in any segment length for the DET and SE, with deeper decreases for longer segments. The intra-patient stability provided large variations in the CV(%) for the DET and even larger for the SE at any segment length. To discern ParAF versus PerAF, correlation matrix filters and Random Forests were employed, respectively, to remove redundant information and to rank the variables by relevance, while coarse tree models were built, optimally combining high-ranked indices, and tested with leave-one-out cross-validation. The best classification performance combined the SE and DF, with an accuracy (Acc) of 88.3%, to discriminate ParAF versus PerAF, while the highest single Acc was provided by the DET, reaching 82.2%. This work has demonstrated that due to the high variability of CFAEs data averaging from one recording place or among different recording places, as is traditionally made, it may lead to an unfair oversimplification of the CFAE-based atrial substrate characterization. Furthermore, a careful selection of reduced sets of features input to simple classification models is helpful to accurately discern the CFAEs of ParAF versus PerAF.

Splitting the P-Wave: Improved Evaluation of Left Atrial Substrate Modification after Pulmonary Vein Isolation of Paroxysmal Atrial Fibrillation.

Atrial substrate modification after pulmonary vein isolation (PVI) of paroxysmal atrial fibrillation (pAF) can be assessed non-invasively by analyzing P-wave duration in the electrocardiogram (ECG). However, whether right (RA) and left atrium (LA) contribute equally to this phenomenon remains unknown. The present study splits fundamental P-wave features to investigate the different RA and LA contributions to P-wave duration. Recordings of 29 pAF patients undergoing first-ever PVI were acquired before and after PVI. P-wave features were calculated: P-wave duration (PWD), duration of the first (PWDon-peak) and second (PWDpeak-off) P-wave halves, estimating RA and LA conduction, respectively. P-wave onset (PWon-R) or offset (PWoff-R) to R-peak interval, measuring combined atrial/atrioventricular and single atrioventricular conduction, respectively. Heart-rate fluctuation was corrected by scaling. Pre- and post-PVI results were compared with Mann-Whitney U-test. PWD was correlated with the remaining features. Only PWD (non-scaling: Δ=-9.84%, p=0.0085, scaling: Δ=-17.96%, p=0.0442) and PWDpeak-off (non-scaling: Δ=-22.03%, p=0.0250, scaling: Δ=-27.77%, p=0.0268) were decreased. Correlation of all features with PWD was significant before/after PVI (p<0.0001), showing the highest value between PWD and PWon-R (ρmax=0.855). PWD correlated more with PWDon-peak (ρ= 0.540-0.805) than PWDpeak-off (ρ= 0.419-0.710). PWD shortening after PVI of pAF stems mainly from the second half of the P-wave. Therefore, noninvasive estimation of LA conduction time is critical for the study of atrial substrate modification after PVI and should be addressed by splitting the P-wave in order to achieve improved estimations.

Quantitative Transthoracic Echocardiography of the Response to Dobutamine in Cardiac Surgery Patients With Low Cardiac Output Syndrome.

OBJECTIVE: To quantify the acute effects of dobutamine in postoperative low cardiac output syndrome (LCOS) using transthoracic echocardiographic, hemodynamic, and blood biomarker monitoring and to assess its association with clinical outcomes. DESIGN: Observational prospective study. SETTING: Single university hospital. PARTICIPANTS: Patients undergoing elective cardiac surgery. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Echocardiographic parameters, hemodynamic data, and plasma biomarkers were obtained before and early after inotrope initiation. The diagnostic value of transthoracic echocardiographic parameters and their association with clinical outcome were evaluated. Thirty-eight LCOS patients and 12 control patients were included. The left ventricular outflow tract velocity time integral was significantly lower in LCOS patients (11.75 v 19.08 cm; p < 0.001) and showed a marked improvement after dobutamine administration (∼37% increase). Dobutamine improved left and right ventricular function, increased mean arterial pressure and urine output, and lowered lactate levels. The duration of dobutamine support, but not in-hospital mortality, was associated with echocardiographic estimates of cardiac performance early after dobutamine initiation. CONCLUSIONS: Early transthoracic echocardiographic assessment and the acute response to inotropic therapy may provide rapid and highly valuable information in the diagnostic workup and risk evaluation of patients with suspected LCOS after cardiac surgery.

Short-Time Estimation of Fractionation in Atrial Fibrillation with Coarse-Grained Correlation Dimension for Mapping the Atrial Substrate.

Atrial fibrillation (AF) is currently the most common cardiac arrhythmia, with catheter ablation (CA) of the pulmonary veins (PV) being its first line therapy. Ablation of complex fractionated atrial electrograms (CFAEs) outside the PVs has demonstrated improved long-term results, but their identification requires a reliable electrogram (EGM) fractionation estimator. This study proposes a technique aimed to assist CA procedures under real-time settings. The method has been tested on three groups of recordings: Group 1 consisted of 24 highly representative EGMs, eight of each belonging to a different AF Type. Group 2 contained the entire dataset of 119 EGMs, whereas Group 3 contained 20 pseudo-real EGMs of the special Type IV AF. Coarse-grained correlation dimension (CGCD) was computed at epochs of 1 s duration, obtaining a classification accuracy of 100% in Group 1 and 84.0-85.7% in Group 2, using 10-fold cross-validation. The receiver operating characteristics (ROC) analysis for highly fractionated EGMs, showed 100% specificity and sensitivity in Group 1 and 87.5% specificity and 93.6% sensitivity in Group 2. In addition, 100% of the pseudo-real EGMs were correctly identified as Type IV AF. This method can consistently express the fractionation level of AF EGMs and provides better performance than previous works. Its ability to compute fractionation in short-time can agilely detect sudden changes of AF Types and could be used for mapping the atrial substrate, thus assisting CA procedures under real-time settings for atrial substrate modification.

Improved Hypertension Risk Assessment with Photoplethysmographic Recordings Combining Deep Learning and Calibration.

Hypertension, a primary risk factor for various cardiovascular diseases, is a global health concern. Early identification and effective management of hypertensive individuals are vital for reducing associated health risks. This study explores the potential of deep learning (DL) techniques, specifically GoogLeNet, ResNet-18, and ResNet-50, for discriminating between normotensive (NTS) and hypertensive (HTS) individuals using photoplethysmographic (PPG) recordings. The research assesses the impact of calibration at different time intervals between measurements, considering intervals less than 1 h, 1-6 h, 6-24 h, and over 24 h. Results indicate that calibration is most effective when measurements are closely spaced, with an accuracy exceeding 90% in all the DL strategies tested. For calibration intervals below 1 h, ResNet-18 achieved the highest accuracy (93.32%), sensitivity (84.09%), specificity (97.30%), and F1-score (88.36%). As the time interval between calibration and test measurements increased, classification performance gradually declined. For intervals exceeding 6 h, accuracy dropped below 81% but with all models maintaining accuracy above 71% even for intervals above 24 h. This study provides valuable insights into the feasibility of using DL for hypertension risk assessment, particularly through PPG recordings. It demonstrates that closely spaced calibration measurements can lead to highly accurate classification, emphasizing the potential for real-time applications. These findings may pave the way for advanced, non-invasive, and continuous blood pressure monitoring methods that are both efficient and reliable.

Dominant frequency and organization index maps in a realistic three-dimensional computational model of atrial fibrillation.

AIMS: To study, using simulation, the spectral characteristics of different patterns of atrial fibrillation (AF) at high spatial resolution. Dominant frequency (DF) and organization index (OI) maps have been used to approximate the location of the focal source of high frequency during AF events. METHODS AND RESULTS: A realistic three-dimensional model of the human atria that includes fibre orientation, electrophysiological heterogeneity, and anisotropy was implemented. The cellular model was modified to simulate electrical remodelling. More than 43 000 electrograms were calculated on the surface, and were processed to reconstitute the DF and OI maps. Atrial fibrillation episodes were triggered by a source of transitory and of continuous activity (both with a cycle length of 130 ms) in five different locations. The maps obtained during the AF events triggered by transitory foci did not show areas with high DF or OI values. When continuous foci were applied, the DF maps show ample zones with high values in the atrium where the focus was applied; while OI maps display smaller areas with high values, always within the areas of high DF and, in three of five locations, this high-value area was located at the site of focus application and at the nearby area. In the other two locations, the area presenting the highest OI values is small and located at the site of focus application, which allowed its precise localization. CONCLUSION: Organization index maps provide a better approximation than DF maps for the localization of ectopic sources of high frequency and continuous activity during episodes of simulated AF in remodelled tissue.

The Relevance of Heart Rate Fluctuation When Evaluating Atrial Substrate Electrical Features in Catheter Ablation of Paroxysmal Atrial Fibrillation.

Coronary sinus (CS) catheterization is critical during catheter ablation (CA) of atrial fibrillation (AF). However, the association of CS electrical activity with atrial substrate modification has been barely investigated and mostly limited to analyses during AF. In sinus rhythm (SR), atrial substrate modification is principally assessed at a global level through P-wave analysis. Cross-correlating CS electrograms (EGMs) and P-waves' features could potentiate the understanding of AF mechanisms. Five-minute surface lead II and bipolar CS recordings before, during, and after CA were acquired from 40 paroxysmal AF patients. Features related to duration, amplitude, and heart-rate variability of atrial activations were evaluated. Heart-rate adjustment (HRA) was applied. Correlations between each P-wave and CS local activation wave (LAW) feature were computed with cross-quadratic sample entropy (CQSE), Pearson correlation (PC), and linear regression (LR) with 10-fold cross-validation. The effect of CA between different ablation steps was compared with PC. Linear correlations: poor to mediocre before HRA for analysis at each P-wave/LAW (PC: max. +18.36%, p = 0.0017, LR: max. +5.33%, p = 0.0002) and comparison between two ablation steps (max. +54.07%, p = 0.0205). HRA significantly enhanced these relationships, especially in duration (P-wave/LAW: +43.82% to +69.91%, p < 0.0001 for PC and +18.97% to +47.25%, p < 0.0001 for LR, CA effect: +53.90% to +85.72%, p < 0.0210). CQSE reported negligent correlations (0.6−1.2). Direct analysis of CS features is unreliable to evaluate atrial substrate modification due to CA. HRA substantially solves this problem, potentiating correlation with P-wave features. Hence, its application is highly recommended.

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. METHODS: A method able to predict robustly long-standing AF early recurrence by characterizing noninvasively the electrical atrial activity (AA) with parameters related to its time course and spectral features is presented. To this respect, 63 patients (20 men and 43 women; mean age 73.4 ± 9.0 years; under antiarrhythmic drug treatment with amiodarone) who were referred for ECV of persistent AF were studied. During a 4-week follow-up, AF recurrence was observed in 41 patients (65.1%). RESULTS: RR variability and the studied AA spectral features, including dominant atrial frequency (DAF), its first harmonic and their amplitude, provided poor statistical differences between groups. On the contrary, f waves power (fWP) and Sample Entropy (SampEn) of the AA behaved as very good predictors. Patients who relapsed to AF presented lower fWP (0.036 ± 0.019 vs 0.081 ± 0.029 n.u.(2) , P < 0.001) and higher SampEn (0.107 ± 0.022 vs 0.086 ± 0.033, P < 0.01). Furthermore, fWP presented the highest predictive accuracy of 82.5%, whereas SampEn provided a 79.4%. The remaining features revealed accuracies lower than 70%. A stepwise discriminant analysis (SDA) provided a model based on fWP and SampEn with 90.5% of accuracy. CONCLUSIONS: The fWP has proved to predict long-standing AF early recurrence after ECV and can be combined with SampEn to improve its diagnostic ability. Furthermore, a thorough analysis of the results allowed outlining possible associations between these two features and the concomitant status of atrial remodeling.

Risk Factors for Postoperative Pacemaker Implantation After Rapid Deployment Aortic Valve Replacement: Results from the RADAR Registry.

INTRODUCTION: Rapid deployment aortic valve replacement has been recently introduced in clinical practice. Different studies have reported a significant reduction in surgical times with excellent hemodynamic profiles and short-term results. However, an increase in permanent pacemaker requirements compared with conventional aortic valve replacement has been described. Nevertheless, risk factors for postoperative pacemaker implantation are not well known. The aim of this study is to report our early outcomes with rapid deployment aortic valve replacement within the RADAR Registry, especially focusing on risk factors for postoperative pacemaker implantation. METHODS: Between April 2012 and January 2016, 164 patients undergoing isolated or combined aortic valve replacement with Edwards INTUITY Elite (Edwards Lifesciences, Irvine, CA, USA) were included in the RADAR Registry. Pre-, intra- and postoperative clinical data results and complications were recorded, especially focusing on risk factors for the development of postoperative complete or high-grade AV block requiring pacemaker implantation. Patients were followed up for up to 1 year with evaluation of clinical and echocardiographic outcomes. RESULTS: A total of 164 consecutive patients were included in this study, where 128 patients (78.05%) had an isolated aortic valve replacement (group 1) and 36 (21.95%) a concomitant procedure (group 2). The surgical approach was ministernotomy in 61 patients (37.20%) and median sternotomy in 100 patients (60.98%). Complications with valve implantation were observed in three patients. Postoperative complete or high-degree AV block requiring a permanent pacemaker implantation developed in ten patients (6.9%). Seven patients died in-hospital (4.27%). No significant differences between groups were found in terms of stroke, postoperative infection, mortality, atrial fibrillation and postoperative atrioventricular block. Seven patients presented acute renal impairment (5.51%) in group 1 versus seven patients (20%) in group 2 (p = 0.007). In multivariate analysis, low weight and preoperative arrhythmia (atrial fibrillation, bifascicular block, left bundle branch block) emerged as risk factors for postoperative AV block requiring a pacer. In median follow-up of 1 year, seven (4.27%) patients died, and no cases of structural valve deterioration or endocarditis were observed. Significant patient-prosthesis mismatch was found in seven (4.27%) patients. CONCLUSION: Initial experience with rapid deployment aortic valve replacement in the RADAR Registry demonstrates low rates of implantation complications and good perioperative and 1-year clinical and echocardiographic outcomes. Incidence of postoperative AV block requiring a pacer correlated with low weight and preoperative arrythmias (atrial fibrillation, bifascicular block and left bundle branch block). Avoidance of oversizing and careful consideration of implantation of this technology in patients with pre-existing arrythmias could minimize the risk for postoperative pacemaker implantation.

Esophagus histological analysis after hyperthermia-induced injury: implications for cardiac ablation.

PURPOSE: To evaluate and numerically score histological alterations observed in the acute phase in the esophagus after being exposed to a hyperthermic dosage and subsequently to correlate the scores obtained with the hyperthermic treatment parameters (i.e. temperature (T) and time (t)). MATERIAL AND METHODS: Esophagus samples obtained from New Zealand white rabbits were immersed in a temperature-controlled saline bath at 40, 50, 60 and 70 degrees C for 30, 60 and 90 s. Samples were then processed for histological analysis (Masson Trichrome technique), and evaluated by searching for objective heat-damage signs. A numerical value was assigned to each sample for each finding. RESULTS: In general, all the layers were affected by the treatment, however, the greatest alterations were found in the epithelium and deeper muscular layers (circular and longitudinal). We found no damage (i.e. no differences to control) in all of the samples treated at 40 degrees C, and severe damage in treatments at 60 and 70 degrees C, regardless of exposure time. On the other hand, samples treated at 50 degrees C did show different results related to time: no damage for 30 s, light damage for 60 s, and moderate damage for 90 s. We assigned a score value to each hyperthermic dosage, and obtained the fitted equation based on a logarithmic transformation of the Arrhenius equation: Score = 130.7 - 40,851/(T + 273) + log t, (R(2) = 0.9326, P < 0.0001). CONCLUSIONS: Hyperthermic treatment mainly affects the epithelium and deeper muscular layers. The results suggest a damage threshold of 50 degrees C for treatments of 30-90 s. The proposed scoring system provides a good fit with the hyperthermic parameters.

Reliability assessment of a cooled intraesophageal balloon to prevent thermal injury during RF cardiac ablation: an agar phantom study.

UNLABELLED: Cooled Balloon Prevents Thermal Injury During RF Ablation. INTRODUCTION: The use of a cooled intraesophageal balloon has recently been proposed to minimize the risk of thermal injury in the esophagus during radiofrequency (RF) ablation of the left atrium. However, the capacity of this device to adequately protect the esophagus under different procedural and anatomical conditions remains unknown. METHODS AND RESULTS: An agar phantom-based model was built that provided temperature readings not only on the cooled balloon (T(b)) but also at a hypothetical point between the esophageal lumen and myocardium at a distance of 2 mm (T(2-mm)). The RF ablations were conducted considering two anatomical factors (total distance between the electrode and balloon and flow rate around the electrode) and two procedural factors (angle and pressure between the electrode and agar surface). The results show that most of the parameters studied have no significant influence on the temperature measured on the cooled balloon (T(b)), the exception being a variation in the flow rate, which was found to influence the temperature. On the other hand, T(2-mm) was affected to a great extent by all the factors considered, the smallest influence being that of the contact pressure. The results also suggest that when an intraesophageal balloon is employed, the applied power is not a good predictor either of the temperature on the balloon or of the temperature measured at a distance 2 mm away. CONCLUSION: The results suggest that a cooled intraesophageal balloon provides effective thermal protection of the esophageal lumen. However, under certain circumstances, the temperature reached at a distance 2 mm away could possibly put at risk the integrity of the inner layers of the esophagus.

A cooled water-irrigated intraesophageal balloon to prevent thermal injury during cardiac ablation: experimental study based on an agar phantom.

A great deal of current research is directed to finding a way to minimize thermal injury in the esophagus during radiofrequency catheter ablation of the atrium. A recent clinical study employing a cooling intraesophageal balloon reported a reduction of the temperature in the esophageal lumen. However, it could not be determined whether the deeper muscular layer of the esophagus was cooled enough to prevent injury. We built a model based on an agar phantom in order to experimentally study the thermal behavior of this balloon by measuring the temperature not only on the balloon, but also at a hypothetical point between the esophageal lumen and myocardium (2 mm distant). Controlled temperature (55 degrees C) ablations were conducted for 120 s. The results showed that (1) the cooling balloon provides a reduction in the final temperature reached, both on the balloon surface and at a distance of 2 mm; (2) coolant temperature has a significant effect on the temperature measured at 2 mm from the esophageal lumen (it has a less effect on the temperature measured on the balloon surface) and (3) the pre-cooling period has a significant effect on the temperature measured on the balloon surface (the effect on the temperature measured 2 mm away is small). The results were in good agreement with those obtained in a previous clinical study. The study suggests that the cooling balloon gives thermal protection to the esophagus when a minimum pre-cooling period of 2 min is programmed at a coolant temperature of 5 degrees C or less.

Restoring sinus rhythm in patients with previous pacemaker implantation submitted to cardiac surgery and concomitant surgical ablation of atrial fibrillation.

OBJECTIVE: Some patients submitted to cardiac surgery have concomitant atrial fibrillation and a previously implanted pacemaker. Because it is unknown if there is any potential for these patients to reassume a regular rate sinus rhythm after ablation of atrial fibrillation, we reviewed the results of all patients with pacemaker enrolled in the Registry of Atrial Fibrillation. MATERIALS: Thirty-six patients were included in this study. Twenty-six had valve disease, seven had coronary disease and three had congenital heart disease. They were submitted concomitantly to ablation of atrial fibrillation using biatrial approaches (seven patients), left sided (27), or right sided (three patients). Thirty-three hospital survivors had a mean follow-up of 18 months, and a maximum of 25 months. RESULTS: At 1 year (n=21), patients' rhythm was sinus non-pacing dependent (52%), sinus pacing-dependent (14%), and atrial fibrillation (14%). At 2 years (n=14), patients' rhythm was sinus non-pacing dependent (57%) and atrial fibrillation (43%). The only factor that may have had impact on the recovery of sinus rhythm at 1 year was the small size of the left atrium (p=0.05). CONCLUSIONS: We conclude that in a significant number of patients, having a pacemaker before surgery does not preclude sinus rhythm recovery after a cardiac operation and ablation for concomitant atrial fibrillation.

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 monitoring during radiofrequency catheter ablation: experimental study based on an agar phantom model.

Although previous studies have established the feasibility of monitoring esophageal temperature during radiofrequency cardiac ablation using an esophageal temperature probe (ETP), some questions remain regarding its efficacy. The aims of this study were to study the effect of the location of the ETP on the temperature reached, and to test the characteristics of ETP as used in clinical practice. We constructed an agar phantom to model the thermal and electrical characteristics of the biological tissues (left atrium, esophagus and connective tissue). The ETP was positioned at 6.5 mm from an ablation electrode and at distances of 0, 5, 10, 15, 20 mm from the catheter axis. A thermocouple was located on the probe to measure the actual temperature of the external esophageal layer during the ablations (55 degrees C, 60 s). The mean temperatures reached at the thermocouple were significantly higher than those measured by the ETP (48.3 +/- 1.9 degrees C versus 39.6 +/- 1.1 degrees C). The temperature values measured with the ETP were significantly lower when the probe was located further from the catheter axis (up to 2.5 degrees C lower when the distance from the probe-catheter axis was 2 cm). The dynamic calibration of the ETP showed a mean value for the time constant of 8 s. In conclusion, the temperature measured by the ETP always underestimates the temperature reached in the thermocouple. This fact can be explained by the distance gap between the thermocouple and probe and by the dynamic response of the ETP. The longer the distance between the ETP and catheter axis, the higher is the temperature difference.