2 Main PointsPR intervalDerivationPreexcitationAV blocks
3 PR interval derivation Measured from beginning of P to beginning of QRS – more properly “PQ”From exiting SA node to leaving terminal perkinjie systemNormal (3-5 small boxes)Allows atrial-assisted filling of ventricles (“timing belt of the heart”)
4 Preexcitation 3 variants, often simply referred to as a group as “WPW” All involve accessory paths that allow direct activation of ventricles without usual av-his-perkinjie delay2 effects – short PR from bypassing normal delaying mechanism, and slurred initial R/S deflection from direct and dyssynchronous activation of ventricle rather than more simultaneous activation from conducting systemDangerous as re-entrant rhythms are much more stable at high rates than normalAV nodal blocking agents should be avoided, as an anti-dromic tachycardia can be inducedInstead of going down the “regular”path and back up the “accessory path”, slow av conduction reverses the flow, so a narrow tachy becomes a wide tachy
5 Pre-excitation – WPW Type 1 – WPW Pathway from atria myocardium to ventricle myocardiumShort PR from bypassing av nodeDelta wave from direct activation of myocardium
6 Preexcitation – James variant Type 2 – James variantPathway from atria myocardium to post AV node his bundleShort PR from bypassing AV nodeNo delta wave, as inserts into normal conducting system
7 Preexcitation – Mahaim variant Type 3 – Mahaim variantPathway from his to myocardiumNormal PR as impulse passed through AVDelta wave as inserts into myocardium
8 AV blocks Type 1 – PR longer than .20 sec Every beat is conducted PR interval is constant
9 AV blocks2nd degree – involve variable PR intervals, with conduction of at least some beatsTypes 2 and Advanced AV block are likely to progress, pacemaker evaluatiion is warrantedThree kinds –Type 1 – progressive PR lengthening (wenkebach)Type 2 – Fixed ratio of p’s make a lesser number of QRS. Conducted p’s have a constant PRAdvanced AV block – Complete AV block with occasional “capture beats” that make it through the AV node.
10 2nd Degree Type 1The RR interval of the pause is less than the two preceding RR intervals, and the RR interval after the pause is greater than the RR interval before the pause.
11 2nd Degree Type 2PR intervals are constant until a nonconducted P wave occurs. The RR interval of the pause is equal to the two preceding RR intervals.
12 Advanced 2nd Degree Block Complete heart block with occaisional “capture beatsCapture beat has a shorter RR than preceding beats
13 3rd Degree AV Block No conducted beats from atria to ventricles P waves with “march through”Width of QRS suggests place of new pacemaker – Wide = ventricular, Narrow = junctional
14 AV dissociation Atria and ventricles march to entirely different drums Not synonymous with complete heart block, although that is one of the causesGenerally can call when v rate is faster than a rate
15 AV dissociation type 1Type 1 occurs when primary pacemaker (SA node) slows to point of normally suppressed pacemaker taking overi.e. sa node slows so junction loses overdrive suppression and takes overKnown as “default”
16 AV dissociation type 2Subsidiary pacemaker accelerates to point where it overdrive supresses SA nodeKnown as “usurpation”
17 AV dissociation type 3Complete heart block with new pacemaker arising below blockClassic AV dissociation/3rd degree heart block we think of