Heart Blocks Leaugeay Webre BS, CCEMT-P, NREMT-P

Atrioventricular Blocks First degree AV block Second- degree Type I (Wenckebach) Second- degree Type II AV Block Third-degree AV block (Complete)

1 st Degree AV Block Arrhythmia in which there is a constant delay in the conduction of electrical impulses, usually through the AV node

Characteristics Abnormally prolonged PR interval PR interval > 0.20 and constant

Diagnostic Characteristics HR- underlying rhythm (sinus or atrial) Rhythm- regular/ underlying rhythm Pacemaker site- underlying rhythm P waves- identical 1:1 conduction PR I- > 0.20 seconds QRS complex- usually normal (0.12 sec)

Cause May be normal Acute inferior or right ventricular MI due to increased vagal tone or AV node ischemia Ischemic heart disease Digitalis toxicity Excessive inhibitory vagal tone Drugs- Ca channel blockers, Beta blockers Electrolyte imbalance- hyperkalemia Myocarditis

Significance Usually not significant Underlying cause should be corrected Usually does not produce Sx

2 nd Degree AV Blocks 2 nd degree Type I AV block- Wenckebach 2 nd degree Type II AV block 2 nd degree 2:1 AV block Advanced or High grade block

2 nd Degree Type I Arrhythmia in which there is a progressive delay following each P wave in the conduction of electrical impulses through the AV node until conduction is completely blocked Most commonly represents defective conduction through the AV node or occasionally in the Bundle of HIS or bundle branches

Characteristics Progressive lengthening of the PR interval until a QRS complex fails to appear after a P wave Repetitive Mobitz type I or Wenckebach

Diagnostic Characteristics HR- underlying sinus or atrial rhythm Rhythm- atrial essentially regular while ventricular is essentially irregular Pacemaker site- underlying rhythm P waves- identical and precede QRS complexes that occur PR interval- gradually lengthen until a QRS complex fails to appear following a non-conducted P wave QRS complex- typically normal

Causes Acute inferior or right ventricular MI due to increased vagal tone or ischemia in the AV node Ischemic heart disease Excessive inhibitory vagal tone Digitalis toxicity Drugs- Beta blockers, Ca channel blockers Electrolyte imbalances- hyperkalemia Myocarditis

Significance Usually transient and reversible Usually produces few Sx May progress to a higher degree block Will respond to atropine if rate requires treatment

2nd degree Type II Mobitz II An arrhythmia in which a complete block of conduction of the electrical impulses occurs in one bundle branch and an intermittent block in the other producing:

Characteristics 1) an AV block with a regularly or irregularly absent QRS complex, commonly producing an AV conduction ratio of 4:3 or 3:2 2) bundle branch block

Diagnostic Characteristics HR- atrial rate of underlying rhythm (sinus, atrial, junctional); ventricular typically less Rhythm- atrial- essentially regular; ventricular – typically regular Pacemaker site- underlying rhythm P wave- identical and precede QRS complexes that occur PR interval- normal or prolonged but constant QRS complex- typically normal may be abnormal with BBB

Conduction Every other P wave conducts QRS 2:1 conduction Every four P waves conducted there are 3 QRS conducted 4:3 Variable conduction will result in irregular ventricular (R-R) rhythm

Cause Extensive damage to the BB i.e. following acute anterior MI May occur in bindle of HIS

Significance More serious Often progresses to 3 rd degree Sx consistent with symptomatic bradycardia Atropine is usually not effective Be prepared for TCP

2 nd Degree 2:1 Advanced AV Block Arrhythmias caused by the defective conduction of electrical impulses through the AV node or the bundle branches or both Produces an AV block characterized by regularly or irregularly absent QRS complexes usually 2:1, 3:1 or > with or without BBB Usually even- 2:1, 4:1…

Diagnostic Characteristics HR- underlying rhythm Rhythm- atrial essentially regular; ventricular regular or irregular depending if variable or constant conduction Pacemaker site- underlying rhythm P wave- identical and precede QRS when they occur PR I- normal or prolonged but constant QRS complex- may be normal or abnormal

Cause 2:1 & Advanced Av blocks with Normal QRS Complexes Usually represent defective conduction of electrical impulses through AV node and are often associated with 2 nd degree Type 1 Acute inferior or right ventricular MI Ischemic heart disease Digitalis toxicity Beta blockers, Ca channel blockers Electrolyte imbalance Myocarditis

Cause 2:1 & Advanced AV Blocks with Abnormal QRS Complexes Usually represent defective conduction of electrical impulse through the bundle branches and are often associated with 2 nd degree Type II Acute anterior MI AV node dysfunction accompanied by preexisting intraventricular conduction disturbance (BBB)

Significance Sx consistent with symptomatic bradycardia 2:1 and advanced with normal QRS complexes often transient Atropine usually effective 2:1 and advanced with abnormal QRS usually progress to 3 rd degree Requires TCP as atropine ineffective

3 rd Degree Av Block Complete absence of conductionof the electrical impulses through the AV node, bundle of HIS, or bundle branches Characterized by independent beating of the atria and ventricles

Diagnostic Characteristics HR- underlying rhythm (sinus, atrial, junctional); ventricle typically may be less, Rhythm- atria regular; ventricles (R-R) regular however, disassociated Pacemaker site- usually sinus, may be atrial or junctional; ventricles escape pacemaker in the Av junction, bundle of HIS, bundle branch, Purkinje P wave- PR interval- vary widely due to no relationship QRS complex- typically exceed 0.12 sec, wide, bizarre

Cause Transient and reversible 3 rd degree AV block is usually associated with normal QRS and HR Acute inferior or right ventricular MI (increased vagal, ischemic AV node) Ischemic heart disease Excessive vagal tone Digitalis toxicity Ca channel blockers, Beta blockers Electrolyte imbalance Myocarditis

Cause Permanent or chronic 3 rd degree is usually associated with wide QRS, HR or < Commonly the result of complete block of both BB Anterior MI Chronic degenerative changes (Lenegre’s, Lev’s diseases) Usually NOT a result of increased vaus stimulation, toxicity

Significance Sx consistent with symptomatic bradycardia, more ominous If Av junction or ventricular escape does not take over following a sudden onset of #rd degree ventricular asystole will occur TCP3 rd degree with narrow QRS may respond to atropine