In this installment of The Scoop, Dr. Laws reviews what is happening during AFib episodes and the effects on the patient’s anatomy over time as the disease is allowed to progress untreated.
The heart is comprised of four main chambers - two top chambers, and two bottom chambers. The top chambers are referred to as the atrial cavities and the bottom chambers referred to as the ventricular cavities. Normal electrical activity originates from within the top right atrial cavity and is generated from the sinoatrial node. This then conducts down to the AV node into the ventricles. There's a sequential activation between the atrial cavities and the ventricles for every cardiac cycle. When atrial fibrillation develops, it usually originates from chaotic electrical activity which originates out of the top left atrial cavity. Invariably, all of the risk factors for development of atrial fibrillation, such as hypertension, valvular heart disease, sleep apnea and diabetes mellitus, lead to increased stretch within the top left atrial cavity. This increased stretch then leads to the development of increased electrical remodeling and ultra-structural changes within the atrial cavity, identified by the presence of fibrosis. Under normal circumstances with gadolinium enhancement, this fibrosis can be visualized with the cardiac MRI imaging. The electrophysiologists at The University of Utah utilized this phenomena to develop the Utah Fibrosis Scoring. The scoring looks at the degree of delayed enhancement within the left atrial cavity. When the degree of delayed enhancement within the left atrial cavity is less than 5%, it is referred to as Utah Heart Classification I and the continuum of delayed enhancement goes up to greater than 35%. When that occurs it is known as Utah Heart Classification IV. These stagings actually have prognostic relevance in development of atrial fibrillation. For instance, when one has a classification of Utah Stage I pulmonary vein isolation, that is the procedural basis for atrial fibrillation ablation, which is usually successful and the risk of recurrence is minimal. When you get to Utah Stage IV ablation techniques are usually not successful and there's a high degree of recurrence. The progression of atrial fibrosis is usually associated with increased stiffness of the left atrial cavity, decreased compliance which overtime leads to dilation of the left atrial cavity which results in a reduction in the systolic function of the left atrial cavity. Hence the left atrial ejection fraction decreases the heart’s ability to pump blood. Ablation techniques and management of risk factors are all aimed at decreasing this phenomenon of atrial fibrosis.
Thanks for your interest in The Scoop. Keep reading the next post to better understand the different types of AFib, and symptoms associated with each variation.