Download Understanding Advances in Clinical Electrophysiology: Updates in

Understanding Advances in Clinical Electrophysiology: Updates in
atrial fibrillation and ventricular tachycardia therapy
Douglas C. Shook, MD
Department of Anesthesiology, Perioperative and Pain Medicine
Brigham and Womens’ Hosptial
Objective: At the conclusion of this lecture, the participant will be able to understand the
advances in clinical electrophysiology
Atrial Fibrillation
There are three reasons to treat atrial fibrillation:
• Reduce symptoms (quality of life)
• Prevent thromboembolism (average annual risk is 5%)
• Prevent cardiomyopathy (treat the tachycardia related to AF)
Rate control vs Rhythm control:
• Recent trials have shown that rhythm control generally doesn’t improve mortality,
stroke, hospitalization, or quality of life compared to rate control.
• Rhythm control maybe may be useful in patients with severe symptoms or in younger
patients.
Anticoagulation:
• Patients with paroxysmal, persistent, and permanent atrial fibrillation have the same
indications for anticoagulation.
• Anticoagulation is indicated when the risk for thromboembolism is greater than the
risk of major bleeding related to warfarin therapy (about 1% per year).
• Risk factors in patients with AF that require consideration for anticoagulation include
>75 years-old, hypertension, heart failure, diabetes mellitus, previous CVA, mitral
stenosis, prosthetic heart valve.
• Warfarin is the anticoagulant of choice in patients with AF. ASA and the combination
of ASA with clopidogrel are not as effective.
• Dabigatran is a direct thrombin inhibitor that has been recently approved by the FDA
for the prevention of CVA and systemic thromboembolism in patients with AF. In a
recent study dabigatran may have better efficacy then warfarin with a similar risk for
major bleeding.
Nondrug therapies:
• For patients who continue to have symptoms after rate control. Usually patients have
failed at least one attempt at rhythm control.
• Ablation of the atrioventricular node followed by permanent pacing is indicated in
patients in whom rapid ventricular response cannot be controlled.
• Electrical isolation of the pulmonary veins. Atrial myocardium extends into the
pulmonary veins, which acts as a trigger to initiate AF. NB: any thoracic vein can
function as a trigger for AF. This ablation technique is most effective in patients with
paroxysmal AF (patients with normal atria).
• Substrate-based ablation is performed in patients with AF triggers related to cardiac
disease, diastolic dysfunction, valvular disease, or enlarged or abnormal, possibly
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fibrotic atria. Percutaneous ablation techniques include those similar to a surgical
maze, ablating high-frequency atrial activity, and targeting atrial parasympathetic and
sympathetic nerves.
In a recent trial, the WATCHMAN device (left atrial appendage occlusion device) was
shown to be as effective in patients with AF in preventing embolism compared to
standard warfarin therapy.
The open surgical maze procedure is still the most effective invasive therapy for AF.
Rarely adopted as a first line treatment.
Percutaneous ablation success:
• Success rate is approximately 60-70% (paroxysmal > chronic).
• 10-40% of patients will require a second procedure.
• 10-15% require continued antiarrhythmic therapies.
Serious ablation complications:
• Pulmonary vein stenosis (4-10%)
• Thromboembolic events (CVA approx 0.5-2.0%)
• Left atrial-esophageal fistula (rare but high fatality rate)
Implantable Defibrillators for the Prevention of Sudden Cardiac Death
Indications:
• Patients resuscitated from sudden cardiac arrest or who previously had a lifethreatening ventricular arrhythmia not related to a transient event or correctable
cause (secondary prevention). Medical therapy is limited (amiodarone) and has
toxicity issues. Implantation of ICDs in this group reduces mortality by 28% and risk
of arrhythmic death by 51%.
• Patients with moderate to severe structural heart disease (ischemic, nonischemic,
hypertrophic cardiomyopathy) with no history of significant ventricular arrhythmia.
This is a much larger treatment group (primary prevention). Post-MI patients with
reduced ejection fraction (EF<30%) had a survival advantage over medical therapy of
23-31% depending on the study. A meta-analysis of all primary prevention trials to
date, including patients with nonischemic cardiomyopathy (EF<30%), showed a 26%
overall reduction in total mortality.
• Patients with miscellaneous cardiac disorders for which the risk of arrhythmic death is
high (inherited diseases of ion channels, long QT syndrome, Brugada syndrome,
catecholaminergic VT, hypertrophic cardiomyopathy, right ventricular dysplasia).
Device testing and quality of life:
• The majority of ICDs placed in the United States are dual-chamber ICDs.
• There are no guidelines regarding the testing of ICDs either at the time of placement
or as routine follow-up.
• Patients who have received a single shock have reported a reduced quality of life.
Other studies have suggested the 5 or more shocks defined the threshold for a
decreased quality of life suggesting the importance of algorithms to prevent
unnecessary shocks delivered for rhythms other than VT/VF and the ability to
terminate stable VT with antitachycardia pacing.
Catheter Ablation for Ventricular Tachycardia
Indications:
• Sustained VT is an important cause of morbidity and mortality.
• Recurrent VT develops in 40-60% of patients who receive an ICD after an episode of
spontaneous sustained VT.
• As stated above, ICD shocks reduce quality of life
• Medical therapy (amiodarone, sotalol) may reduce VT episodes but can have toxic
side effects.
• VT ablation can reduce episodes of VT and terminate incessant VT or VT storm.
Types of VT:
• The appearance of VT on the ECG suggests its underlying cause and associated
heart disease.
• Monomorphic VT (same QRS complex from beat to beat)  indicates repetitive
ventricular activation from a focus that can be targeted for ablation. Most ventricular
reentry rhythms are due to ventricular scar (post-MI, cardiomyopathies, surgical
incisions).
• Polymorphic VT (the QRS changes from beat to beat)  functional reentry without a
structural target for ablation. (acute-MI, abnormalities of ion channels, idiopathic
ventricular fibrillation, structural disease such as hypertrophy, recent MI,
cardiomyopathy).
Ablation procedure:
• Vascular access is obtained.
• The VT is induced to confirm the diagnosis and to establish if treatable with catheter
ablation.
• Mapping is performed to locate the source and target the ablation catheter.
• Testing is performed to assess the effect or success of the ablation. Abolishing
incessant VT and inducible clinical VT is the minimum end point that defines a
successful procedure.
• Ablations can be both endocardial and epicardial depending on the location of the VT
focus.
Complications:
• Steam pops  the radiofrequency current used for ablations causes steam formation
that can explode through the tissue (tamponade can occur).
• The risk of tamponade is greater with ablations involving the right ventricle (thin
walled).
• Risk of thrombus formation with ablation catheters.
• Damage to the aortic or mitral valve gaining access to the LV.
• Vascular access complications.
• Cerebral or systemic embolism (up to 2.7%)
• Atrioventricular nodal block (especially with VT that originates from the septum)
• With epicardial ablation risk of coronary artery injury is a major concern
• Damage to the left phrenic nerve as it courses down the lateral aspect of the LV
For further review of atrial fibrillation and ventricular tachycardia therapies in the
electrophysiology lab see the suggested reading below which formed the basis of this
outline and presentation:
Zimetbaum P. In the clinic. Atrial fibrillation. Ann Intern Med;153:ITC61-15, quiz ITC616.
• Medical diagnosis and treatment decisions related to atrial fibrillation
Crandall MA, Bradley DJ, Packer DL, Asirvatham SJ. Contemporary management of atrial
fibrillation: update on anticoagulation and invasive management strategies. Mayo Clin Proc
2009;84:643-62.
• A comprehensive review of the latest atrial fibrillation therapies (a must read if you go
to the EP lab)
Marcus GM, Scheinman MM, Keung E. The year in clinical cardiac electrophysiology. J Am
Coll Cardiol 2010;56:667-76.
• A yearly review of the best studies in cardiac electrophysiology
Passman R, Kadish A. Sudden death prevention with implantable devices. Circulation
2007;116:561-71.
• An excellent review of ICD indications and management.
Stevenson WG, Soejima K. Catheter ablation for ventricular tachycardia. Circulation
2007;115:2750-60.
• A comprehensive review of VT ablation procedures (must read if you go to the EP
lab)
Shook DC, Savage RM. Anesthesia in the cardiac catheterization laboratory and
electrophysiology laboratory. Anesthesiol Clin 2009;27:47-56.
• A review of anesthetic issues encountered in the EP lab.