![]() Myocardial cells in this region display a shorter refractory period compared to surrounding myocardium and patients without AF. Pulmonary vein isolation (PVI) performed during catheter ablation for AF aims to isolate this region from the surrounding myocardium dissipating further development of AF. The most common site for ectopic foci and trigger origin is the left atrial muscular sleeve extending into the pulmonary vein. Re-entry circuits arise, which in turn gives rise to new impulse waves generating additional re-entry circuits that help maintain persistent arrhythmia to overcome such blocks. When these impulses encounter the myocardium with variable excitability or refractoriness, it gives rise to functional electrical blocks. Impulses from such extrasystoles, however, are discharged at high frequency. This after-depolarization can cause extra systole but cannot maintain persistent arrhythmia. Triggers arise when the action potential induces after-depolarization that is strong enough to overcome recovering repolarization. ![]() Triggers are responsible for initiating the event (arrhythmia), and substrate will maintain that arrhythmia. The underlying mechanism for AF is related to a complex interaction between triggers and substrate. The American Heart Association and American College of Cardiology further classified AF as follows: ![]() Typically the heart rate varies from 120 to 160 beats per minute however, heart rate as fast as 200 beats per minute can be seen. Ventricular response to atrial activation depends on the conduction properties of the AV node. As a result of the above effects, atrial contractility is lost, causing an inability to completely empty blood from the atrial appendage leading to the risk of clot formation and subsequent thromboembolic events. AF is the most common sustained arrhythmia characterized by disorganized, rapid, and irregular atrial activation leading to an irregular ventricular response. Atrial fibrillation (AF) is a subtype of SVT that causes an irregularly irregular heart rhythm. Examples of SVT include atrial flutter, atrial fibrillation (AF), atrioventricular nodal reentrant tachycardia (AVNRT), also known as paroxysmal supraventricular tachycardia (PSVT), atrioventricular reentrant tachycardia (AVRT), and multifocal atrial tachycardia (MAT). All pathological arrhythmia can be further classified based on heart rate into tachyarrhythmia (fast), bradyarrhythmia (slow), or tachy-brady (fast-slow) arrhythmia.Īll tachyarrhythmia originating above the ventricles, including atria and atrioventricular node (AV node), are grouped under supraventricular tachycardia (SVT). As the name suggests, sinus arrhythmia originates from the sinus node, but the regularity between each heartbeat varies with inspiration and expiration. ![]() Arrhythmias are almost always pathological except sinus arrhythmia, which is physiological. ![]() Abnormal heart rate or rhythm, which is not physiologically justified, is known as arrhythmia. The stimulus for each heartbeat commonly originates from the sinus node in the right atria, hence the name sinus rhythm. The succession of 3 such regular heartbeats displaying identical waveform leads to a steady rhythm. A normal heartbeat consists of a sequential contraction of atria followed by ventricles in a series of cardiac cycle events. ![]()
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