Second-degree atrioventricular block, type 1. Some, but not all, atrial beats are getting through to the ventricles. There is progressive elongation the the P-R intervals until on P wave is completely dropped. These are usually due to reversible ischemia of the AV node, often associated with acute myocardial infarction. The ischemic node is slow to recover after each depolarization, which results in longer and longer nodal delay until one impulse isn't conducted. Treatment rarely needed.
ATRIOVENTRICULAR NODE (AV NODE) - part of the electrical control system of the heart that coordinates the top of the heart. It electrically connects atrial and ventricular chambers. AV node is an area of specialized tissue between atria & ventricles of the heart, specifically in the posteroinferior region of the interatrial septum near the opening of the coronary sinus, which conducts the normal electrical impulse from the atria to the ventricles | Wikipedia
ELECTRICAL CONDUCTION SYSTEM OF THE HEART - Normal intrinsic electrical conduction of the heart allows electrical propagation to be transmitted from the Sinoatrial Node through both atria and forward to the Atrioventricular Node. Normal/baseline physiology allows further propagation from the AV node to the ventricle or Purkinje Fibers and respective bundle branches and subdivisions/fascicles. Both the SA and AV nodes stimulate the Myocardium | Wikipedia
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Electrical signals fire from multiple locations in the atria, causing abnormal quivering of the atria (1). The atrioventricular node — your heart's natural pacemaker — is unable to prevent all of these chaotic signals from entering the ventricles (2). Your ventricles respond to these extra, chaotic signals by beating faster than normal (3).
AVRT (Atrioventricular reentrant tachycardia) seen in patients with WPW syndrome. electrical impulse make a circuit, which consists of an anterograde limb(normal pathway) and a retrograde limb(accessory pathway). impulse start from atrium → AV node(anterograde) → His-Purkinje → ventricle → accesory pathway(retrograde) → back to atrium narrow QRS regular tachycardia negative P waves seen after QRS complex. no delta wave, since antegrade conduction is not occurring via the accessory pathway