###### Created: 2024-06-14 13:35 ###### Areas & Topics: #medicine #cardiovascular ###### Note Type: #permanent ###### Connected to: [[Peri-Arrest Rhythms]] [[Atrial Fibrillation]] - Atrioventricular (AV) Block, also known as Heart Block or Conduction Disorder, is a condition where there is a delay or disturbance in conduction between the atria and ventricles. - AV blocks can be temporary or permanent, and are broken down into three types depending on their severity. - The most common cause of AV Blocks are idiopathic fibrosis and sclerosis of the conduction systems of the heart. ### First-Degree AV Block - First-Degree AV Block is defined as a consistent prolongation of the PR Interval (i.e. more than 0.2 seconds) - In First-Degree AV Block, impulses between the atria and ventricles are slowed but can still reach the ventricles, meaning no beats are dropped and there is a 1:1 ratio of P-Waves to QRS Complexes. - First-Degree AV Block is a common and often incidental finding. #### ECG - Regular Rhythm - Sinus Rhythm (P-Waves are all followed by a QRS) - Prolonged PR Interval - Normal QRS Complexes ![[First-degree-heart-block.jpg]] #### Clinical Features - Patients with First-Degree AV Block are typically asymptomatic. - If patients are symptomatic a pacemaker can be considered. ### Second Degree AV Block (Type 1) - Second-degree AV block (type 1) is also known as Mobitz Type 1 AV block or Wenckebach phenomenon. - It involves the PR Interval progressively getting longer until an impulse is not conducted to the ventricles, at which point a QRS Complex is dropped. - Following this, the sequence repeats until another QRS is dropped (creating a regularly irregular rhythm). #### ECG - Regularly Irregular Rhythm - P-Waves are normal but aren't always followed by a QRS complex - PR Interval gets longer until a QRS is dropped - Normal QRS Complexes ![[Second-degree-heart-block-mobitz-1.jpg]] #### Clinical Features Common findings of Second-Degree AV Block (Type 1) can include: - Irregular Pulse - Bradycardia - Pre-Syncope/Syncope #### Management - Second-Degree AV Block (Type 1) is typically benign and doesn't require treatment for asymptomatic patients. - If patients are symptomatic a pacemaker can be considered. ### Second Degree AV Block (Type 2) - Second-degree AV block (type 2) is also known as Mobitz type 2 AV block. - In this type, the PR Interval is consistent but QRS complexes are dropped at random points whenever conduction fails. - It normally follows a repeating cycle following every 3rd or 4th P Wave, represented as a ratio (i.e. 3:1 block, 4:1 block etc.) #### ECG - Irregular Rhythm (can be regularly irregular) - P-Waves are normal but there are more P-Waves than QRS Complexes - Consistent PR-Interval - QRS Complexes can be normal or broad (if conduction failure is located distal to the bundle of His) ![[Second-degree-heart-block-mobitz-2.jpg]] #### Clinical Features Common findings of Second-Degree AV Block (Type 2) can include: - Irregular Pulse - Palpitations - Pre-Syncope/Syncope #### Management - Second-Degree AV Block (Type 2) can progress to Third-Degree (Complete) Heart Block, so patients should be placed on a cardiac monitor ASAP. - If no reversible causes are identified, then a permanent pacemaker can be inserted. ### Third Degree (Complete) AV Block - Third Degree Heart Block is also known as Complete Heart Block - It occurs when there is no electrical communication between the atria and ventricles. - This means that P-Waves and QRS complexes will have no association on ECG (as the atria and ventricles are operating independently) #### ECG - Variable Rhythm - No association between P-Waves and QRS Complexes (but both present) - Absent PR Interval (as there is no AV dissociation) ![[Third-degree-complete-heart-block.jpg]] ![[pdd534b.png]] #### Clinical Features Common findings of Third-Degree AV Block can include: - Irregular Pulse - Bradycardia (normally profound) - Palpitations - Pre-Syncope/Syncope - Confusion - Breathlessness - Haemodynamic Compromise - Sudden Cardiac Death #### Management - Patients should be placed on a cardiac monitor ASAP and treated via Peri-Arrest Guidelines (see [[Peri-Arrest Rhythms]]). - A permanent pacemaker is normally required long term. ### Resources Kashou AH, Goyal A, Nguyen T, et al. Atrioventricular Block. [Updated 2024 Feb 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK459147/ Atrioventricular Block - Geeky Medics https://geekymedics.com/atrioventricular-block/