Atrial fibrillation, often called AF, causes the heart to beat rapidly and irregularly and frequently causes symptoms such as chest pain, shortness of breath, light headedness and palpitations until it either stops racing or is slowed by medications. Because AF prevalence is increasing due to the aging population, the costs to the healthcare system are significant – $815 million dollars in Canada in 2010 alone.
A relatively minimally invasive therapy, called catheter ablation, delivers treatment to the sources of AF to prevent it from coming back. Studies have consistently shown that once a patient has failed an anti-arrhythmic drug, ablation is far better at preventing future AF. Because of the good results, catheter ablation has grown rapidly. Unfortunately, a first procedure works only 50-70% of the time and a second procedure is common. Often this is due to small gaps in the therapy, and easily treated at a short second procedure. New technologies are promising to limit the number of gaps that need to be redressed.
In some patients, ablation fails to work because the atria (top chamber of the heart where AF originates) are so severely diseased that ablation is unlikely to make a significant impact regardless of the number of ablation procedures. In such patients repeated failed ablation offers little benefit but repeated risks of 3% per procedure. A method of measuring the severity of the atrial disease prior to ablation would allow patients and their physicians to make better decisions. Alternative therapies, like AV node ablation and pacemaker might be chosen instead, with maintenance of a high quality of life without repeated ineffective ablation procedures and the associated risk of serious complication.
In this research program, we will perform 3 consecutive projects designed to develop atrial imaging as a new tool (project 1), incorporate the atrial imaging tool into patient care (project 2) and test to make sure it works (project 3).
Project 1 will develop new imaging methods, like MRI and PET scanning, to measure the severity of disease in the atria. The work we propose will bring together Canada’s most skilled heart imaging scientists, experts in MRI and PET from multiple centers (Ottawa, London and Calgary) to collaborate on new methods of atrial disease imaging. Most centers, even large, well known US centers, work independently using a single imaging method (either MRI alone or PET alone). By forming a new network and working collaboratively, in a unique arrangement using multiple imaging methods, the network promises to develop new imaging tools that are directly correlated to the severity of atrial disease.
In project 2, we will incorporate the new imaging tools developed in project 1, with other patient characteristics, like age and duration of AF, to develop a tool that will predict outcomes for catheter ablation of AF. Our hope is to identify those patients who are unlikely to benefit from ablation despite several ablations, so that this can be avoided. In a second group of patients we will directly test our tool and validate it to make sure it works the way we want.
Project 3 will be the ultimate and most critical test of our tool using a method called a randomized control trial. We expect that, by identifying patients with severe atrial disease and poor outcomes predicted, alternative treatments will be used to maintain a high quality of life without repeated ineffective ablation procedures.
Currently, a massive effort in developing a pre-clinical model of AF and the needed PET imaging, MRI imaging, voltage mapping and histological (microscopic anatomy) tools to follow the progression of heart tissue remodeling and associated functional deterioration has been completed. Preliminary results in this pre-clinical model of left atrial disease are showing that MRI has the capacity to identify abnormal tissue in the left atrium but it now has to be compared to the truth by performing electrical mapping of the left atrium and histological analysis of normal and abnormal left atrial tissue where the tissue sampling locations are guided by MRI. This is the first time in the world that answers to the important question as to what the abnormal tissue seen in MRI actually correponds to can now be addressed so that effective clinical trials can be properly designed.
We anticipate that the outcomes of ablation will be improved resulting in more effective care for all patients with AF, either by getting very effective ablation care or by getting very effective alternative therapy without repeated ineffective ablation procedures. Also importantly, we hope to improve the efficiency of AF care in the Healthcare system by reducing AF ED visits and hospitalizations, improving care for all Canadians with AF.