Bradycardia and Heart Block Notes


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Atrioventricular block

Bundle branch block

NOTES NOTES BRADYCARDIA & HEART BLOCK GENERALLY, WHAT ARE THEY? PATHOLOGY & CAUSES ▪ Delay or complete blockage in the electrical conduction system of the heart → abnormal heart rhythm; primarily, bradycardia SIGNS & SYMPTOMS ▪ If symptomatic, may present as lightheadedness, headache, syncope, palpitations, Stokes–Adams attacks, fatigue, dyspnoea etc. CAUSES ▪ Can be caused by defect in ▫ Atrioventricular node ▫ Bundle branches ▫ Sinoatrial node ▪ Idiopathic or secondary to ▫ Myocardial ischemia ▫ Fibrosis ▫ Infections ▫ Congenital heart disease ▫ Cardiomyopathies ▫ Iatrogenic (e.g. medication, postsurgery) COMPLICATIONS ▪ May progress to fatal arrhythmias, heart failure, and/or sudden cardiac death DIAGNOSIS ▪ ECG-based; see individual disorders TREATMENT ▪ May not require treatment MEDICATIONS ▪ E.g. atropine OTHER INTERVENTIONS ▪ Transcutaneous pacing ▪ Pacemaker implantation OSMOSIS.ORG 21
ATRIOVENTRICULAR BLOCK PATHOLOGY & CAUSES ▪ Blockage/delay in electrical signal stimulating contraction between atria, ventricles TYPES ▪ First degree atrioventricular (AV) block ▪ Second degree atrioventricular block ▫ Type I/Mobitz I/Wenckebach ▫ Type II/Mobitz II ▪ Third degree atrioventricular block/complete heart block CAUSES Congenital heart disease Heart damage ▪ Infiltrative/dilated cardiomyopathies, muscular dystrophy, lyme disease, myocardial ischemia, myocarditis, endocarditis with abscess, hyperkalemia, high vagal tone Iatrogenic causes ▪ Medication (beta blockers, calcium channel blockers, cardiac glycosides), post-cardiac surgery, post-catheter ablation, posttranscatheter aortic valve implantation Lev’s disease/Lenegre-Lev syndrome ▪ Idiopathic fibrosis and calcification of heart’s electrical conduction system, most common in elderly COMPLICATIONS ▪ Heart failure secondary to bradycardia; third degree AV block risk for sudden cardiac death 22 OSMOSIS.ORG SIGNS & SYMPTOMS ▪ Presence/severity depends on ventricular rate ▫ Lightheadedness, syncope, fatigue, dyspnea DIAGNOSIS OTHER DIAGNOSTICS ECG ▪ First-degree AV block ▫ Signal delayed; continues to ventricles ▫ PR interval > 200ms due to delayed ventricular contraction ▪ Second degree AV block ▫ Type I/Mobitz I/Wenckebach: PR interval lengthens with each beat until blocked completely (e.g. progressive PR intervals : 200ms → 260ms → 300ms → dropped beat; no QRS). Ventricular escape beat: if ventricle does not receive signal from atrioventricular node after short time, latent pacemaker cells within bundle of His/ventricle kick in, begin pacing heart at slower than normal rate (~20–50bpm) ▫ Type II/Mobitz II: prolonged PR interval (> 200ms). Block commonly in bundle of His → QRS usually wide (> 110ms), intermittent dropped beats (no QRS). Happens randomly; no progressive lengthening of PR interval; every second P wave blocked, may progress to third degree AV block ▪ Third degree AV block/complete heart block ▫ Signal completely blocked every time ▫ Eg. ventricles contract at lower rate than atria (ventricular pacemaker cells establish rate) ▫ No association between P waves, QRS complexes
Chapter 4 Bradycardia & Heart Block TREATMENT ▪ Depends on type/severity ▫ For all: identify electrolyte imbalances/ medication-induced causes ▪ No treatment: ▫ First degree AV block, asymptomatic type I second degree MEDICATIONS MNEMONIC AV blocks If the R is far from P, then you have a First Degree. Longer, longer, longer, drop! Then you have a Wenckebach. If some P’s don’t get through, then you have Mobitz II. If P’s and Q’s don’t agree, then you have a Third Degree. ▪ Atropine: second degree, third degree OTHER INTERVENTIONS Permanent pacemaker ▪ Asymptomatic: type II second degree, third degree ▪ Symptomatic: type I & II second degree, third degree Transcutaneous pacing ▪ Symptomatic: type I & II second degree, third degree Figure 4.1 ECG (lead II) demonstrating first degree atrioventricular block. Figure 4.2 ECG (lead V1) demonstrating Mobitz I (Wenckebach) second degree atrioventiricular block. OSMOSIS.ORG 23
Figure 4.3 ECG (lead V1) demonstrating Mobitz II second degree atrioventricular block. Figure 4.4 ECG (lead V1) demonstrating third degree (complete) atrioventricular block. BUNDLE BRANCH BLOCK PATHOLOGY & CAUSES ▪ Electrical signal for contraction of left/right ventricle completely blocked or delayed Intermittent bundle branch block ▪ Occasional block, unrelated to heart rate TYPES Rate-related bundle branch block ▪ Block occurs when heart rate is relatively fast, temporarily resolves once heart rate slows down ▪ Either right or left bundle branch blocks can be complete or incomplete ▫ Complete: total blockage of signal transmission ▫ Incomplete: slowed signal transmission Right bundle branch block (RBBB) ▪ Signal blocked in right bundle branch ▫ Left ventricle contracts first → signal carried to right side via Purkinje fibers → right ventricle contracts Left bundle branch block (LBBB) ▪ Signal blocked in left bundle branch ▫ Right ventricle contracts → left ventricle contracts Bilateral bundle branch block ▪ Caused by disease involving both right/left bundle branches; on ECG, indistinguishable 24 from complete heart block and may lead to ventricular asystole OSMOSIS.ORG CAUSES ▪ Fibrosis/scarring, formed acutely/chronically Acute ▪ Ischemia, myocardial infarction, myocarditis ▪ Sudden increase in right ventricular pressure → pulmonary embolism ▪ Iatrogenic: right heart catheterization/ ethanol ablation of basal ventricular septum Chronic ▪ Gradual remodelling of heart muscle ▫ Hypertension, coronary artery disease, cardiomyopathies ▫ Pulmonary hypertension ▫ Congenital heart disease
Chapter 4 Bradycardia & Heart Block RISK FACTORS ▪ Increasing age, associated with underlying or advancing heart disease SIGNS & SYMPTOMS RBBB ▪ Asymptomatic; wide splitting on auscultation LBBB ▪ Asymptomatic; reversed splitting on auscultation ▪ LBBB only ▫ Negative V1, positive V6 (away from V1 towards V6) ▫ V1: QS, or “little r”-rS complex. W shape ▫ V6: large, notched R wave. M shape ▪ RBBB only ▫ Positive V1,negative V6 ▫ V1: large terminal R wave. M shape ▫ V6: slurred S wave, W shape TREATMENT ▪ No treatment DIAGNOSIS OTHER DIAGNOSTICS ECG ▪ LBBB and RBBB ▫ Lead II (limb lead) shows long QRS complex > 120ms (normal: 80–120ms) ▫ Longer QRS complex because depolarization starts on time but ends later due to depolarization delay in one ventricle MNEMONIC: WiLLiaM MaRRoW ECG of Left BBB W-shape in V1 Left BBB Left BBB has V6 M-shape ECG of Right BBB M-shape in V1 Right BBB Right BBB has V6 W-shape Figure 4.5 Illustration depicting mnemonic “WiLLiaM MaRRoW.” OSMOSIS.ORG 25
Figure 4.6 ECG demonstrating left bundle branch block. Figure 4.7 ECG demonstrating right bundle branch block. 26 OSMOSIS.ORG
Chapter 4 Bradycardia & Heart Block Figure 4.8 Illustration depicting wide QRS in bundle branch block. Figure 4.9 Illustration depicting M-shape and W-shape in bundle branch blocks. OSMOSIS.ORG 27
SICK SINUS SYNDROME SIGNS & SYMPTOMS PATHOLOGY & CAUSES ▪ Malfunction in sinoatrial node (SA node) characterized by persistent spontaneous sinus bradycardia, alternating sinus bradycardia and tachyarrhythmia (sometimes called tachycardia-bradycardia syndrome) ▪ Stokes–Adams attacks (fainting due to asystole/ventricular fibrillation), syncope, palpitations, chest pain, dyspnea, fatigue, headache, nausea ▪ Variable ECG findings DIAGNOSIS CAUSES ▪ Disorders causing scarring/degeneration/ damage to SA node ▫ Sarcoidosis, amyloidosis, hemochromatosis, Chagas disease, cardiomyopathies ▪ Can be caused/worsened by certain medications ▫ Digoxin, calcium channel blockers, beta blockers, anti-arrhythmics ▪ Congenital ▫ Mutations of SCN5A gene encoding alpha subunit of sodium ion channel RISK FACTORS ▪ ▪ ▪ ▪ Elderly Coronary artery disease High blood pressure Aortic, mitral valve diseases COMPLICATIONS ▪ Sinus arrest, sinus node exit block, sinus bradycardia ▫ May be associated with tachycardia (characterized by long pause after tachycardia), e.g. atrial tachycardia, atrial fibrillation ▫ Associated with azygos continuation of interrupted inferior vena cava 28 OSMOSIS.ORG DIAGNOSTIC IMAGING ECG OTHER DIAGNOSTICS ▪ Tilt table testing ▪ Holter monitor TREATMENT OTHER INTERVENTIONS Pacemaker implantation ▪ For hemodynamically stable individuals, tachycardia can be treated with medication; can be combined with pacemaker in some cases ▪ For hemodynamically unstable individuals, definitive therapy requires pacemaker implantation; medication plays limited role

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