Abnormal Cardiac Conduction & Rhythm

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  1. SA Node
    • 60-100bpm
    • 60% Right coronary artery
    • 40% Left circumflex artery
    • Sympathetic and parasympathetic innervation
  2. AV Node
    • 85-90% Right coronary Artery
    • 10-15% Left circumflex coronary artery
    • Sympathetic and parasympathetic innervation
  3. Right Bundle Branch
    • Thin bundle of fibers coursing down the RV and branching at the RV apex
    • More vulnerable to interruption due to late branching
    • Blood from the left anterior descending coronary a.
  4. Left Bundle Branch
    • Branches into left anterior superior fascicle and left posterior inferior fascicle (less vulnerable to interruption).
    • Blood from the left anterior descending coronary a. 
    • Left posterior inferior fascicle also receives good from the posterior descending coronary artery and is more difficult block.
  5. PR Interval
    • Time between atrial and ventricular depolarization
    • 0.12-0.2 sec
  6. QRS Complex
    • Ventricular depolarization
    • 0.05-0.1 sec
  7. ST Segment
    • Ventricular depolarization to ventricular repolarization
    • T wave should be the same direction as QRS
  8. Mechanisms of Tachydysrhythmias
    • 1. Increased Automaticity in normal conduction tissue or in an ectopic focus
    • 2. Re-entry of electrical potential through abnormal pathways
    • 3. Triggering of abnormal cardiac potentials due to after-depolarizations.
  9. Sinus Dysrhythmia
    • Irregular sinus rhythm 
    • Bainbridge reflex: normal variation during inspiration (+HR) and expiration (-HR)
  10. Sinus Tachycardia
    • Common SVT dysrhythmia w/ MI
    • 100-160bpm
    • Normal P wave before QRS
    • Tx: Underlying condition, B-blocker, supplemental O2, avoid vagolytic drugs
  11. Premature Atrial Beats (PACs)
    • Ectopic foci in atria
    • Dx: early, abnormally shaped P wave w/ variable PR interval, NOT followed by a compensatory pause
    • Tx: avoid sympathetic stimulation and eliminate drugs that may induce PACs. 
    • Suppressed with Ca Channel blockers or Beta-blockers.
  12. Supraventricular Tachycardia (SVT)
    • 160-180bpm 
    • Initiated at or above AV node
    • Usually paroxysmal (unlike sinus tachycardia)
    • AV nodal re-entrant tachycardia (AVNRT) is most common
    • Tx: vagal maneuver, adenosine, B-blocker, Ca channel blocker
    • Adenosine: rapid onset and offset
    • Anesthesia: avoid sympathetic, electrolyte imbalance, and acid-base disturbance
    • 3x more in women
    • Polyuria due to increased ANP from increased atrial pressures
  13. Multifocal atrial Tachycardia
    • Irregular rhythm
    • P wave with 3 or more morphologies and variable PR intervals. 
    • Tx: underlying condition (methylxanthine toxicity, acute exacerbation of chronic lung disease, CHF, sepsis, metabolic/ electrolyte abnormalities). Bronchodilators (for lungs), O2, and magnesium (2g over 1hr), Verapamil. B-blockers (cardioversion has NO EFFECT)
  14. Atrial Flutter
    • 250-350bpm
    • Sawtooth "F waves"
    • Tx: cardioversion (often less than 50J)
    • Initial goal: ventricular rate control with amiodarone, diltiazem, verapamil)
  15. Atrial Fibrillation
    • Loss of AV synchrony and rapid heart rate associated with dysrhythmia
    • No discernable P waves
    • Rapid ventricular response seen w/ accessory tracts (wide QRS)
    • Thromboembolic event likely causing a stroke due to stasis of blood and atrial thrombi formation
    • Tx: Electrical cardioversion (100-200J), amiodarone, propafenone, ibulitide, sotalol
    • Ventricular control: B-blockers, Ca channel blockers, and digoxin
    • Often underlying HTN and ischemic heart disease
    • IV heparin is most common preoperative drugs
    • Anesthesia: close monitoring of Mg and K concentrations
  16. Premature Ventricular Contractions (PVCs)
    • Premature wide QRS complex, no P wave, ST segment and T wave inversion, and compensatory pause. 
    • R on T phenomenon in vulnerable period at the middle third of T wave
    • Tx: underlying cause, defibrillator present, B-blockers
    • Progression to ventricular tachycardia: amiodarone, lidocaine, and other antidysrhythmics. 
    • Associated: ischemia, valve disease, cardiomyopathy, prolonged QT, electrolyte abnormalities,
  17. Ventricular Tachycardia
    • Usually 150-200bpm
    • Regular rhythm, Wide QRS, no P waves
    • Torsades de pointes (polymorphic ventricular tachycardia) from prolonged QT
    • Tx: cardioversion, amiodarone (150mg over 10 min), procainamide, sotalol, and lidocaine, Beta blockers, Ca channel blockers, acid base/ electrolyte disturbance
  18. Ventricular Fibrillation
    • Irregular ventricular rhythm, no BP or CO
    • Tx: Electrical defibrillation (3-5 min) is the only method capable of generating a CO, followed by 1mg of epinephrine or 40units vasopressin
    • DDx: hypoxia, hypovolemia, acidosis, hypokalemia, hyperkalemia, hypoglycemia, hypothermia, drug/ toxins, cardiac tamponade, tension pneumothorax, ischemia, pulmonary embolus, hemorrhage.
  19. Wolff-Parkinson-White Syndrome
    • Info: pre-excitation and tachydysrhythmia (often AVNRT) causing an earlier than normal deflection of the QRS complex called a delta wave. 
    • Orthodromic AVNRT: Narrow QRS Complex, through AV node, treated with vagal maneuver, adenosine, verapamil, B-blockers, or amiodarone
    • Antidromic AVNRT: Wide QRS, atrium to ventricle through accessory pathway, treat with procainamide or amiodarone (not AV conduction dependent like adenosine, verapamil, B-blockers, digoxin), and possibly electrical cardioversion
    • WPW w/ AFib: Procainamide
    • Anesthesia: Continue antidysrhythmics, avoid events or drugs that enhance anterograde conduction of cardiac impulses through accessory pathways
  20. Prolonged QT Syndrome
    • Info: Congenital and acquired versions. Abnormal depolarization allows after-depolarizations to trigger PVCs which intimate a ventricular reentry rhythm of polymorphic ventricular tachycardia (TdP). QTc exceeding 460-480msec. 
    • Tx: electrolyte correction (Mg or K), B-blocker, cardiac pacing, ICD implant
    • Anesthesia: Isoflurane and sevoflurane prolong QT, droperidol and other antiemetics (ondansetron) prolong QT, avoid abrupt increases in sympathetic, acute hypokalemia (hyperventilation)
  21. Sinus Bradycardia
    • Under 60bpm, regular rhythm, P wave before each QRS
    • Tx: eliminate excess vagal tone, transcutaneous/ transvenous pacing, Atropine (0.4mg IV every 3-5min max 3mg), epi/dopamine infusions, glucagon (3mg bolus w/ 3mg/hr) if unresponsive due to B-blocker or Ca channel overdose
    • Sick Sinus Syndrome: dysfunction of the SA node
  22. Junctional Rhythm
    • Nodal rhythm of 40-60bpm which can be conducted retrograde into the atria. 
    • Tx: junctional rhythm due to myocarditis, ischemia, or digitalis toxicity should be managed by treating the underlying disorder. Atropine can be given if it becomes hemodynamically significant.
  23. First Degree AV Block
    • S/S: Prolonged PR Interval Greater than 0.2sec w/ normal QRS. Sometimes due to drugs, ischemia, or increased parasympathetic
    • Tx: Usually asymptomatic w/ no treatment. Sometimes correct ischemia, atropine may be used but contraindicated in patients w/ significant heart disease
    • Anesthesia: Avoid increased vagal tone or slower AV, maintain normal K levels
  24. Second Degree AV Block: Mobitz I (Wenckebach)
    • S/S: Progressive prolongation of PR interval w/ a dropped beat (absolute refractory period). May be due to ischemia, fibrosis/ calcification, or infiltrative/inflammatory disease of myocardium, or drugs (Ca channel blockers, B-blockers, sympatholytics). Usually asymptomatic.
    • Tx: Usually none needed. Atropine or pacing may be used. 
    • Anesthesia: Control ventricular response. Usually no changes are needed.
  25. Second Degree AV Block: Mobitz Type II
    • S/S: Complete interruption in the conduction of a cardiac impulse below the AV node (Bundle of His area). Usually symptomatic. Higher chance of profession to 3rd degree.
    • Tx: Transcutaneous/ transvenous pacing. Atropine for bradycardia. 
    • Anesthesia: May need a cardiac pacemaker if it progresses to 3rd degree.
  26. Right Bundle Branch Block
    • S/S: More common than LBBB without structural heart disease. Seen w/ ASD, valvular disease, and ischemic heart disease. Bifasicular block more commonly seen w/ left anterior
    • ECG: Widened QRS and an RSR' in V1/V2. Deep S wave in Leads I/V6
    • Tx: observation and elimination of contributing factors. Pacing in event of progression to 3rd degree. 
    • Anesthesia: No major changes. Avoid significant changes in BP, arterial O2, and serum electrolytes. No prophylactic cardiac pacemaker.
  27. Left Bundle Branch Block
    • S/S: Often a marker of heart disease (HTN, CAD, aortic valve disease, and cardiomyopathy). Anterior hemiblock is more likely. May be seen during tachycardia or HTN and is a sign of ischemia. 
    • ECG: QRS over 0.12sec and no P waves in Leads I/V6
    • Tx: Some only have LBBB above a critical heart rate. Tx underlying condition such as ischemic heart disease, LV hypertrophy, or cardiomyopathy
    • Anesthesia: Pulmonary catheter may cause 3rd Degree block if RBBB occurs.
  28. Third Degree AV Block
    • S/S: Complete interruption of AV conduction w/ no association between P wave and QRS complex. May signal acute inferior wall MI. Stoke-Adams attack may cause syncope. CHF may occur from bradycardia due to 3rd degree block. 
    • ECG: Ectopic pacemaker near the AV node has a rate of 45-55bpm and a narrow QRS. An infranodal pacemaker has a rate of 30-40bpm and a wide QRS complex. Lenegre's disease is fibrotic degeneration of the distal cardiac conduction system due to aging. Lev's disease is calcific changes in more proximal conduction tissue. 
    • Tx: Transcutaenous/ transvenous pacing. 
    • Anesthesia: Isoproterenol may be needed to maintain HR. Antidysrhythmics may suppress the ectopic ventricular pacemaker.
  29. Treatment of Cardiac Dysrhythmias
    Abnormal physiological parameter should be corrected prior to drug therapy: Acid base levels, normal serum electrolytes, and ANS stabilization
  30. Adenosine
    • Dose: 6mg (2nd dose may be given)
    • Alpha Agonist
    • Drug of choice for termination of stable AVNRT and certain SVTs
    • Rapid injection followed by 20ml bolus
    • SA: facial flushing, dyspnea, and chest pressure. 
    • Contra: Sick sinus syndrome, 2nd&3rd degree blocks
  31. Amiodarone
    • Dose: 150/300mg
    • Alpha and Beta-blocking effects that prolong the refractory period
    • Antidysrhythmic to tx VFib and pulseless VT
    • Metabolized by the liver and increases amount of warfare, quindine, procainaimide
  32. Beta-Blockers
    • Decrease HR and BP
    • Indicated in patients with presered LV function who require ventricular rate control in AFib, Aflutter, and narrow complex tachycardias above the AV node
    • SAs: Bradycardia, AV conduction delays, and hypotension
    • Contra: 2nd or 3rd degree block, hypotension, severe CHF, and reactive airway disease. NOT useful for AFib or Aflutter w/ WPW syndrome.
  33. Ca Channel Blockers
    • Verapamil (2.5-5mg over 2min): slows conduction and increases refractory of the AV node. Tx narrow tachycardia (SVT) with failed vagal maneuvers and adenosine. Ventricular rate control for AFib/AFlutter 
    • Diltiazem (0.25mg/kg over 2min): Less negative inotropic effects as verapamil and less peripheral vasodilation.
  34. Digoxin
    • Cardiac glycoside to tx CHF and AFib
    • Positive inotrope, increses phase 4 depolarization time, shortens the action potential (decreasing conduction velocity through AV node and prolongs refractory period).
  35. Lidocaine
    • Dose: 1-1.5mg/kg
    • Na Channel Blocker
    • Tx: Ventricular ectopy and short bursts of VTach. Alternative to amiodarone in arrest w/ VFib or pulseless VTach
    • SA: CNS toxicity of tinnitus, drowsiness. Some myocardial depression and node dysfunction with other antidysrhythmics. Extensive first pass hepatic metabolism.
  36. Magnesium
    • Dose: 1-2g over 5min.
    • Tx: Torsades de Pointes or Polymorphic ventricular tachycardia
  37. Procainamide
    • Dose: 50mg/min titrated to effect
    • Class I Antidysrhythmic: Slows conduction, decreases automaticity, and increases refractory period. 
    • Tx: VTach w/ pulse, Aflutter, AFib, AFib w/ WPW, and SVT resistant to adenosine and vagal (ALL w/ presered ventricular function)
    • SAs: hypotension, QRS prolongation
  38. Epinephrine
    • Dose: 1mg every 3/5min
    • Vasopressor w/ alpha and Beta effects
  39. Vasopressin
    • Dose: 40units
    • Peripheral vasocontrictor (not Alpha or beta)
    • Antidiuretic hormone
  40. Atropine
    • Dose: 1mg every 3/5min
    • Vagolytic/ Anticholinergic: Increase HR, BP, and SVR
  41. Isoproterenol
    • Dose: 1mcg/min titrated (10mcg for bronchospasm)
    • B1 and B2 agonist
    • Increased inotropy and chronotrophy
    • Dilates coronary vessels, but increased B1 increases cardiac oxygen demand more than supply
    • Tx: symptomatic bradycardia
  42. Dopamine
    • Low (3-5 mcg/kg/min): Increases renal, mesenteric, coronary and cerebral flow through DA receptors
    • Moderate (5-7mcg/kg/min): Beta effects predominate
    • High (>10mcg/kg/min): Alpha stimulation causes peripheral vasoconstriction and reduction in renal flow. 
    • Tx: sympatomatic bradycardia unresponsive to atropine.
  43. Electrical Cardioversion
    • 2 chest electrodes: anterior and posterior
    • If given during the T wave, it could cause VTach or VFib 
    • Start with 50-100J
    • Synchronized: SVT, AFlutter, and AFib and chronic/stable rate controlled AFlutter or AFib to sinus rhythm, and VTach w/ pulse
    • Risk: Systemic embolism, so anticoagulation is recommended if over 48 hours.
  44. Defibrillation
    • Monophasic/biphasic
    • 150/200 J
    • Do not place electrodes over pulse generators or ICDs.
  45. Radiofrequency Catheter Ablation
    Intracardiac electrode cathode in a large vein to produce thermal injury to destroy myocardial tissue responsible for dysrhythmias
  46. Artificial Cardiac Pacemakers
    • Transcutaneous Pacing: Symptomatic bradycardia or sever conduction block requiring immediate pacing. Chest and back electrodes over areas of less skeletal mass
    • Implanted cardiac pacemaker: Long term treatment for sinus bradycardia and SSS
  47. Implantable Cardioverter-Defibibrillator
    • Single most important factor in determining survival from cardiac arrest due to VFib is the time between arrest and the 1st defibrillation attempt. 
    • Delivers a shock within 15sec of dysrhythmia onset.
  48. Surgery With Cardiac Devices
    • Preoperative: Determine reason for device, consult w/ cardiologist, and representative for specific device
    • Management: Drugs not altered by properly placed device. Electrocautery pulse should be minimized and grounding far away from the pulse generator. Avoid hyperkalemia (succinylcholine), hypokalemia (hyperventilation), arterial hypoxemia, myocardial ischemia/infarction, and catecholamine 
    • Anesthesia: Drugs such as atropine or isoproterenol should be available is a decreased HR compromises hemodynamics.

Card Set Information

Author:
 doza04
ID:
 307590
Filename:
 Abnormal Cardiac Conduction & Rhythm
Updated:
2015-09-15 23:59:08
Tags:
Anesthesia Conduction Rhythm
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Description:
Anesthesia for Abnormal Cardiac Conduction & Rhythm
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