intraoperative arrhythmias

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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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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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

intraoperative arrhythmias

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