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C24 Cardiology and Cardiac Surgery
Arrhythmias
Toronto Notes 2019
Systematic Review: Implantable Cardioverter Defibrillators for Adults with Left Ventricular Systolic Dysfunction
Ann Intern Med 2007;147:251-262
Study: Meta-review of 12 RCTs used for ICD efficacy, 5 RCTs and 48 observational studies for effectiveness, and 21 RCTs and 43 observational studies for safety review.
Population: 8,516 patients for ICD efficacy, 26,840 patients for effectiveness, and 86,809 patients for safety review with left ventricular ejection fraction ≤0.35.
Intervention: ICD implantation.
Outcomes: All-cause mortality and adverse events. Results: ICDs reduced all-cause mortality by
20% (95% CI, 10%-29%; I2=44.4%) with greatest reduction (54%) in sudden cardiac death (CI 37%- 63%; I2=0%). Observational studies had a reduced relative risk of 0.54 for all-cause mortality versus RCTs (CI 0.43-0.58, I2=60.4%). Rates of success of ICD implantation were 99% (CI 98.8%-99.3%) with a 1.2% (CI 0.9%-1.5%) chance of peri-implantation death. Post-implantation complications (per
100 patient yr) were: 1.4 (CI 1.2-1.6) device malfunctions; 1.5 (CI 1.3-1.8) lead problems; 0.6 (CI 0.5-0.8) implant site infection and 19.1 (CI 16.5-22.0) inappropriate discharges in RCTs versus a rate of 4.9 (CI 4.5-5.3) inappropriate discharges in observational studies.
Conclusion: ICDs are safe and effective in reducing mortality in adult patients with LV
systolic dysfunction but carry significant risks of inappropriate discharges. Differences between RCTs and observational studies show that improved risk stratification of patients may further improve outcomes and reduce adverse events.
Management
• acute:resuscitatewithpromptCPRanddefibrillation
• investigateunderlyingcause(cardiaccatheterization,electrophysiologicstudies,echo) • treatunderlyingcause
• antiarrhythmicdrugtherapy:amiodarone,β-blockers
• implantablecardioverterdefibrillator(ICD)
• refertoACLSguidelines(seeAnesthesiaandPerioperativeMedicine,A12)
Electrophysiology Studies
• invasivetestfortheinvestigationandtreatmentofcardiacrhythmdisordersusingintracardiaccatheters • providedetailedanalysisofthearrhythmiamechanismandprecisesiteoforiginwhenECGdataare
nondiagnostic or unobtainable
• bradyarrhythmias:definethemechanismsofSAnodedysfunctionandlocalizesiteofAVconduction
block
• tachyarrhythmias:mapforpossibleablationortoassessinducibilityofVT
Electrical Pacing
• thedecisiontoimplantapacemakerusuallyisbasedonsymptomsofabradyarrhythmiaor tachyarrhythmia in the setting of heart disease
Pacemaker Indications
• SAnodedysfunction(mostcommon):symptomaticbradycardia±hemodynamicinstability • commonmanifestationsinclude:syncope,presyncope,orseverefatigue
• SAnodedysfunctioniscommonlycausedby:intrinsicdiseasewithintheSAnode
(e.g. idiopathic degeneration, fibrosis, ischemia, or surgical trauma), abnormalities in autonomic
nervous system function, and drug effects
• AV nodal-infranodal block: Mobitz II, complete heart block
Pacemaker Complications
• complicationsrelatedtosurgicalimplantationincludevenousaccess(pneumothorax,hemothorax,air embolism), pacemaker leads (perforation, malposition), pocket hematomas and infection
• complications specific to the pacemaker include a failure to pace, failure to sense, pulse generator failure, pacemaker syndrome and pacemaker mediated tachycardia
Pacing Techniques
• temporary:transvenous(jugular,subclavian,femoral)orexternal(transcutaneous)pacing • permanent: transvenous into RA, apex of RV, or both
• cansenseandpaceatrium,ventricle,orboth
• newgeneration:rateresponsive,abletorespondtophysiologicdemand
• biventricular
Implantable Cardioverter Defibrillators
• suddencardiacdeath(SCD)usuallyresultsfromventricularfibrillation(VFib),sometimesprecededby monomorphic or polymorphic ventricular tachycardia (VT)
• ICDsdetectventriculartachyarrhythmiasandarehighlyeffectiveinterminatingVT/VFibandin aborting SCD
• mortality benefit vs. antiarrhythmics in secondary prevention
• benefitseeninpatientswithischemicandnon-ischemiccardiomyopathy,depressedleftventricular
ejection fraction (LVEF), prolonged QRS
• seeHeartFailure,C34forcurrenttreatmentrecommendations
Catheter Ablation
Techniques
• radiofrequency(RF)ablation:alow-voltagehigh-frequencyformofelectricalenergy(similarto cautery); RF ablation produces small, homogeneous, necrotic lesions approximately 5-7 mm in diameter and 3-5 mm in depth
• cryoablation:newtechnologywhichusesaprobewithatipthatcandecreaseintemperatureto-20˚C and -70˚C. Produces small, necrotic lesions similar to RF ablation; when brought to -20˚C, the catheter tip reversibly freezes the area; bringing the tip down to -70˚C for 5 min permanently scars the tissue
■ advantage: can “test” areas before committing to an ablation
■ disadvantage: takes much longer than RF (5 min per cryoablation vs. 1 min per RF ablation)