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8/11/2019 Intraoperative Arrhythmias
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Occurrence: 15-85%Rare complication resulting from cardiacarrhythmia in the healthy patientsLife-threatening arrhythmia during surgery Fewer than 1% of patients Almost all have cardiac disease
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Physiology
The Action Potential
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Physiology
The Action Potential Spontaneous diastolic depolarization
Resting potential not stable in conductive tissue cellSlow spontaneous depolarization until the thresholdpotential is reached
Slope is controlled by ANS
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Physiology
The Action Potential Excitability: depolariztion to specific stimulus
Increased excitability depolarization to a lesser stimuls or an exaggerated
response to normal stimulus
RefractorinessAbsolute refractory period: phase 0,1,2Relative refractory period: late phase 3, early 4
Susceptable to strong stimuli
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Physiology
The Conduct System
most rapid conduction
Control
ventricularresponse toincreased supraventricular rates
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Physiology
Electrophysiology of Arrhythmias Disturbance of SA nodal rate Reentry-associated arrhythmias
Alternate pathwaysOne-way or unidirectional block in one pathway
An area of slow conduction in the other pathway
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Diagnostic Criteria
Supraventricular Arrhythmias Rate
150 - atrial flutter with 2:1 AV block>200 - accessory AV pathway
Regularity
AF: irregular rhythmRegular SVT with variable AV block may bemisleading
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Diagnostic Criteria
Supraventricular Arrhythmias P waves
Presence of P wave before QRS: atrial originNo P wave with regular tachycardia: AV node orbelow
QRS width
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Diagnostic Criteria
Supraventricular Arrhythmias QRS axis
Severe LAD: ventricular origin Paroxysmal SVTSinoatrial node reentry: normal PAtrial tachycardias: upright but abnormal appearing P
Atrioventricular node reentry: no P or invertedAccessory pathway: delta waveAF: irregular narrow QRSA-flutter: atrial rate 300 with AV block
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Diagnostic Criteria
Ventricular Arrhythmias Frequent PVCs, couplets or brief runs of VT
Healthy persons: benignPresence of cardiac dis or LV dysfunction: dangerous
Frequent PVCs(> 6/min) after MI: increased
mortality risk
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Cause and Significance
Congenital Mostly benign Accessory pathway tachycardia: compromise
hemodynamic stability Congenital prolonged Q-T interval: predispose to
vetricular arrhythmia
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Cause and Significance
Acquired Vetricular arrhythmia
IHD., aortic stenosis, dis. associated with LVH Atrial fibrillationIHD., related to aging, distened aorta (MS, CHF)
Acquired prolonged Q-T intervalIHD., electrolyte abnormality, drug side effectProgress polymorphic ventricular tachycardia(torsades de pointes)
CNS dis, ICH, stroke: all types of SVT andvetricular arrhythmia
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Cause and Significance
Electrolyte Imbalance Low potassium may trigger dangerous vetricular
arrhythmia Low magnesium produce primarily SVT Acute changes in pHAnesthesia Calcium antagonistic properties Halothane: sensitize the heart to catecholamines
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Treatment
Class I Block the fast Na channel & decrease the rate of
rapid depolarization Class IA
Vagolytic action, decrease contractility, -adrenergicblockadeQuinidine, disopyramide, procainamide,diphenylhydantoin
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Treatment
Class I Class IB
Lidocaine Used in all types of vetricular arrhythmia Except vetricular arrhythmia d/t prolonged Q-T interval Toxic effect: CNS activation
Class ICSuppressor of phase 0 sodium conductanceIncreased mortality risk
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Treatment
Class II -adrenergic receptor blockers Effective in all tachyarrhythmias Perioperative management of congenital
prolonged Q-T interval
Toxicity related to bronchoconstriction
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Treatment
Class III Prolong reploarization Increase action potential duration & the effective
refractory period Bretylium
Facilitation of ventricular defibrillationEffective in bupivacaine-induced arrhythmias
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Treatment
Class IV Calcium channel antagonists
Supraventricular tachyarrhythmias: useful Ventricular tachycardias: ineffective, severe
cardiac dysfunction
Potentiate the myocardial effects of anesthetics Contraindication: AF with WPW syndrome
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Treatment
Adenosine Effective in acutely converting reentrant nodal
SVT & accessory pathway SVTDigoxin Perioperatively maintain rate control in A-flutter
& AFMagnesium ion Useful in the period around CPB operations
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Conclusion
Tx only associated with hemodynamiccompromise and potential to progress to life-
threatening arrhythmiasMust be familiar with only selective drug