Pathophysiology

Pathophysiology Study Guide

©2018 of 131 case where this enhanced automaticity occurs after every normal sinus beat, it is termed as atrial bigeminy. Reentry In the case of reentry, the normal electric activity of the heart is disturbed. In the initial depolarization phase, a group of isolated fibers is not activated. Before the impulse dies out, excitability is recovered and act as a link to re-excite areas that were depolarized previously and have recovered from initial depolarization. There are two categories of reentry: classic or anatomical reentry and functional reentry. The major difference between the two is the existence of anatomical structures in the circuit in classic reentry. With functional reentry, the circuit is determined by dynamic heterogeneities in electrophysiological features of the tissue. Some types of functional reentry include leading circle, anisotropic reentry, the figure of 8 reentry, reflection, and spiral wave reentry. In a reentry, the myocardial tissue is joined with different electrophysiological properties, conduction, and refraction essential, acting as a substrate. There should also be an area of block due to the presence of unexcitable tissues, which obstruct the normal circulation of the wave. There will be a unidirectional conduction block. The path of the conduction will be slowed down, causing a delay in circulating wave front conduction, and triggering the recovery of refractory tissue to the site of unidirectional blockage. Abnormal Conduction Pathways The progression of the electrical impulse through the heart resulting in the beating of the heart is known as conduction. Disorders of the conduction system can happen in three ways: delay in one particular point, total interruption in the pathway, and non-responsiveness of some part in the conduction pathway. The first one is known as first-degree heart block, which is characterized by a delay in the atrioventricular conduction. This delay causes the elongated time interval between the atria and ventricles conduction. The second one is the second-degree heart block in which the ventricle conduction is half of atria. In this case, every alternate heart beat is blocked, and hence, do not reach the ventricle. The third type denotes complete blockage of the heart as the pathway between the atria and ventricles is fully stopped. In this case, the atria and ventricles beat independent of each other, and the rate of ventricular is much slower than atrial rate. Another conduction disorder is Wolff-Parkinson-White syndrome. This is a pre-excitation arrhythmia in which the accessory tract triggers the conduction of the impulses from atria to ventricles. This accessory tract is not located at the normal conduction system of the heart. The conduction system between the two chambers of the heart is short-circuited and specific parts of the ventricular muscle are prematurely stimulated. This causes distortion of the QRS system in the electrocardiogram. In some cases, a fatal arrhythmia is developed due to abnormal bypass tract. Reentry arrhythmia can also be developed when the conduction time between the normal atrial and ventricular waves are impaired, and instead the bypass tract is activated. This causes the ventricle wave to reach the atrium through another pathway. This can be treated with antiarrhythmic drugs and catheter or surgical ablation, depending on the severity of the case. Achieve Page 48