A Review on Atrial Fibrillation (Computer Simulation and Clinical Perspectives)

Atrial fibrillation (AF), a heart condition, has been a well-researched topic for the past few decades. This multidisciplinary field of study deals with signal processing, finite element analysis, mathematical modeling, optimization, and clinical procedure. This article is focused on a comprehensive review of journal articles published in the field of AF. Topics from the age-old fundamental concepts to specialized modern techniques involved in today’s AF research are discussed. It was found that a lot of research articles have already been published in modeling and simulation of AF. In comparison to that, the diagnosis and post-operative procedures for AF patients have not yet been totally understood or explored by the researchers. The simulation and modeling of AF have been investigated by many researchers in this field. Cellular model, tissue model, and geometric model among others have been used to simulate AF. Due to a very complex nature, the causes of AF have not been fully perceived to date, but the simulated results are validated with real-life patient data. Many algorithms have been proposed to detect the source of AF in human atria. There are many ablation strategies for AF patients, but the search for more efficient ablation strategies is still going on. AF management for patients with different stages of AF has been discussed in the literature as well but is somehow limited mostly to the patients with persistent AF. The authors hope that this study helps to find existing research gaps in the analysis and the diagnosis of AF.

Echocardiography-guided percutaneous per-ventricular laser ablation of ventricular septum: in vivo study in a canine model

Surgical myectomy and ethanol ablation are established intervention strategies for left ventricular outflow obstruction in hypertrophic cardiomyopathy. Safety and efficacy limitations of these interventions call for a minimally invasive, potentially safer, and more efficacious strategy. In this study, we aimed to evaluate the feasibility of echocardiography-guided percutaneous per-ventricular laser ablation of a ventricular septum in a canine model. Six domestic dogs were chosen for the study. A 21G needle was inserted into the right ventricle with its tip reaching the targeted basal to mid-septum, after which laser ablation was performed as follows: 1-W laser for 3 min (180 J) at the basal segment and 5 min (300 J) at middle segment of the septum, respectively. Echocardiography, blood chemistry tests, and pathology examination were performed to assess the results of laser ablation. No death or major complications, i.e., tamponade, pericardial effusion, or ventricular fibrillation, occurred. The laser-ablated areas were well demarcated in the results of the pathological examination. The diameters of the ablated regions were 4.42 ± 0.57 and 5.28 ± 0.83 mm for 3 and 5 min ablation, respectively. Pre-ablation and post-ablation, cardiac enzymes were found to increase significantly while no significant differences were found among M-mode, 2D (LVEF), pulsed-wave (PW) Doppler, and tissue Doppler imaging (TDI) measurements. Contrast echocardiography confirmed the perfusion defects in the ablated regions. Microscopically, the ablated myocardium showed coagulative changes and a sparse distribution of disappearing nuclei and an increase in eosinophil number were observed. Our study suggests that percutaneous and per-ventricular laser ablation of the septum is feasible, potentially safe and efficacious, and warrants further investigation and validation.

Histopathology of Bipolar Radiofrequency Ablation in the Human Atrium

BACKGROUND

The Cox maze IV operation has become the preferred surgical treatment for atrial fibrillation, as it is associated with less morbidity and complexity than the Cox maze III procedure, yet is still highly effective. Numerous studies have been conducted in animals to examine the histopathology of this operation on the heart but studies on human hearts that have undergone the Cox maze IV operation have not been performed.

METHODS

We report the histopathologic findings in 3 patients from whom tissue was available for histologic study. In 2 patients it was obtained at autopsy within a month after undergoing a Cox maze IV operation, and in the remaining patient, atrial tissue was obtained immediately after ablation.

RESULTS

The lesions were clearly visible on the atria at day 6 and day 18. Microscopic examination showed that the hearts were in different stages of healing. We also found that, compared with animal models, human myocardium had significant preexisting underlying damage with myocyte hypertrophy and fibrosis. Although most of the ablative lesions were transmural, not all spanned from the epicardium to the endocardium. The chronic changes present in these hearts may have prevented transmurality by impeding energy delivery from fully penetrating the tissue.

CONCLUSIONS

The atrial myocardial substrate studied in experimental conditions is markedly different from the human hearts that frequently express histopathologic changes secondary to the underlying disease process. That may prevent creating true transmural lesions and impact final efficacy of the procedure.

Surgical therapy of atrial fibrillation

Atrial fibrillation (AF) can be found in an increasing number of cardiac surgical patients due to a higher patient's age and comorbidities. Atrial fibrillation is known, however, to be a risk factor for a greater mortality, and one aim of intraoperative AF treatment is to approximate early and long-term survival of AF patients to survival of patients with preoperative sinus rhythm. Today, surgeons are more and more able to perform less complex, that is, minimally invasive cardiac surgical procedures. The evolution of alternative ablation technologies using different energy sources has revolutionized the surgical therapy of atrial fibrillation and allows adding the ablation therapy without adding significant risk. Thus, the surgical treatment of atrial fibrillation in combination with the cardiac surgery procedure allows to improve the postoperative long-term survival and to reduce permanent anticoagulation in these patients. This paper focuses on the variety of incisions, lesion sets, and surgical techniques, as well as energy modalities and results of AF ablation and also summarizes future trends and current devices in use.

Surgical treatment of lone atrial fibrillation

Currently, off-pump video-assisted thoracoscopic epicardial pulmonary vein isolation offers an attractive alternative to on-pump Maze procedures for surgical treatment of lone atrial fibrillation. Nevertheless, on-pump Maze procedures through a mid-sternotomy approach still play an important role in patients with lone atrial fibrillation on many occasions, especially in patients with failed percutaneous pulmonary vein alone. The aim of this article was to give a brief review of the surgical strategies for treating lone atrial fibrillation, and present the possible indications for on-pump Maze procedures through a mid-sternotomy approach.

A strategic approach for cardiac MR left ventricle segmentation

Quantitative evaluation of cardiac function from cardiac magnetic resonance (CMR) images requires the identification of the myocardial walls. This generally requires the clinician to view the image and interactively trace the contours. Especially, detection of myocardial walls of left ventricle is a difficult task in CMR images that are obtained from subjects having serious diseases. An approach to automated outlining the left ventricular contour is proposed. In order to segment the left ventricle, in this paper, a combination of two approaches is suggested. Difference of Gaussian weighting function (DoG) is newly introduced in random walk approach for blood pool (inner contour) extraction. The myocardial wall (outer contour) is segmented out by a modified active contour method that takes blood pool boundary as the initial contour. Promising experimental results in CMR images demonstrate the potentials of our approach.