Anesthetic Challenges in the EP Lab: High-Acuity Patient in an Offsite
Environment
Nelson L. Thaemert, M.D.
Assistant Program Director, Cardiothoracic Anesthesia Fellowship
Associate Clinical Director
Brigham & Women’s Hospital
Harvard Medical School
Background
Cardiac arrhythmias are a significant source of patient morbidity and
mortality. Each year, more than 40,000 patients suffer cardiac arrhythmia related
death and over 800,000 arrhythmia related hospitalizations occur in the United
States. Treatment for arrhythmias includes medical management, device therapy
and interventional ablative procedures. Indeed, the Electrophysiology Lab provides
a venue for diagnostic and therapeutic treatment for a large number of these
patients. Over the past 20 years, the EP lab has moved from a largely diagnostic
theater to a predominantly therapeutic one. Examples of procedures performed
include implantation of permanent pacemakers for bradyarrhythmias, multiple
pacer leads for cardiac resynchronization therapy (CRT) for heart failure,
implantable cardioverter defibrillators (ICDs) for lethal tachyarrhythmias, and
transcatheter ablations for a variety of abnormal heart rhythms. Understanding
these procedures is an important element for any medical provider caring for these
patients, including referring practitioners, electrophysiology interventionalists, and
anesthesia providers.
Arrhythmia Mechanisms and Basis for Treatment
Arrhythmias arise from a variety of mechanisms. Bradyarrhythmias are due
to a failure of impulse generation or propagation. Sinoatrial node dysfunction can
manifest as sinus bradycardia, sinus arrest, or tachy-brady syndrome (also known
as sick sinus syndrome) when bradycardia alternates with paroxysms of atrial
fibrillation. Conversely, failure of impulse propagation manifests as one of several
types of heart block at the atrioventricular node.
Tachyarrhythmias occur largely through three mechanisms: increased
automaticity, triggered activity, and reentry. Increased automaticity can occur
through a variety of metabolic disturbances that result in abnormal automaticity of
atrial or ventricular muscle cells that do not normally have pacemaker activity.
These disturbances include ischemia, hypoxia, hypokalemia, hypomagnesemia, acidbase disorders, increased sympathetic tone and use of sympathomimetic agents.
Triggered activity is rhythmic cardiac activity that results when a series of
afterdepolarizations reach the threshold potential, as is seen in patients with
congenital or acquired prolonged QT syndrome who develop triggered ventricular
tachycardia. Reentry is the most common mechanism for tachyarrhythmias, and is
the cause for supraventricular tachycardias like atrioventricular nodal reentrant
tachycardia (AVNRT), Wolff-Parkinson-White (WPW) syndrome with an accessory
pathway, typical and atypical atrial flutter, atrial fibrillation and monomorphic
ventricular tachycardia.
Two principal goals of medical management of arrhythmias are reduction in
risk of stroke and alleviation of symptoms. Patients with both paroxysmal and
persistent atrial fibrillation as well as those with ventricular tachycardia related to
extreme cardiomyopathy and poor ventricular function are frequently treated with
oral anticoagulants. Symptom relief of atrial fibrillation can be achieved with either
rate control or rhythm control strategies. Unfortunately, limitations of
antiarrhythmic agents include inconsistent efficacy in maintaining sinus rhythm and
frequent side effects. Indeed, medical treatment of ventricular tachycardia is limited
by high failure rates, potential for proarrhythmia and frequent toxicity.
Device therapy in the Electrophysiology lab can treat a variety of conditions.
Implanted single or dual chamber pacemakers can treat bradyarrhythmias of SA or
AV nodal origin. Biventricular pacers for resynchronization therapy (CRT) in the
setting of ventricular failure can improve symptoms and functional status.
Implantable cardioversion defibrillators (ICDs) can target lethal ventricular
arrhythmias including ventricular tachycardia and ventricular fibrillation for either
primary or secondary prevention of sudden cardiac death.
Interventional therapy directed against arrhythmias include catheter based
techniques and surgery. These therapies are indicated when medical management
has failed to maintain a sinus rhythm and provide sufficient control of symptoms, or
when a potentially curative lesion is identified. Endovascular catheter based
ablations can treat AVNRT, WPW, other Supraventricular Tachycardias, Atrial
Flutter, Atrial Fibrillation, and Ventricular Tachycardia. Epicardial approaches in
the EP lab may also be undertaken for certain VT lesions. Finally, open surgical
approaches to arrhythmia management include epicardial ablations in patients with
VT circuits inaccessible with percutaneous techniques and cryoablative MAZE
procedures for AFib.
Overview of Anesthesia in the EP Lab
Most procedures in the EP Lab require a spectrum of sedation and anesthesia
related services. Indeed, device implantations and transcatheter ablations have a
host of anesthetic considerations, and staffing in this arena should pair patients and
providers together with appropriate skills. Most device implantations are
performed with light sedation and local anesthetic. Certain catheter based
ablations, such as for WPW, AVNRT, other SA nodal or reentrant tachycardias, and
atrial flutter are relatively short in duration and can safely be performed with the
patient breathing spontaneously under moderate sedation. In our institution, a
registered nurse trained in conscious sedation performs sedation for most devices
or simple ablations. In contrast, atrial fibrillation and ventricular tachycardia
ablations may take several hours, frequently require general anesthesia and may
present a variety of hemodynamic abnormalities. These advanced interventions
have specific requirements and pose specific challenges to both the anesthesiologist
and the proceduralist.
Performing anesthesia out of the operating room poses multiple risks, but
the most significant one is the lack of immediate help in case of emergencies.
Limited resuscitative equipment availability, limited human resources with
appropriate anesthetic skills for immediate help, and potential for cardiovascular
catastrophe during the procedure all heighten the risks of this expanding arena of
medical care. Appropriate planning for emergencies is crucial for long-term success
of providers in this setting.
Environmental challenges exist in the EP Lab. In most settings, the lab is
composed of a procedure room connected to an external control booth. Distance
and mechanical barriers can hamper communication between providers. Extensive
use of fluoroscopy during ablation procedures requires protection of providers from
radiation, providing further barriers to communication and limiting access to the
patient. Anesthesia machines and ventilators may require repositioning after
movement of biplane fluoroscopy arms. Anesthesia breathing circuits and
intravenous lines may require extensions, and sudden movement of the procedure
table can lead to disastrous disconnects. The importance of good communication in
this setting cannot be overstated.
Knowledge and understanding of the steps of a complex ablative procedure
may be the biggest limitation for anesthesia providers new to this setting. Planning
an appropriate anesthetic requires understanding the potential pitfalls that may
surround general anesthesia, neuromuscular blockade, and hemodynamic
stimulation. All patients require standard ASA monitors, defibrillator pads,
capnography, oxygen and resuscitative equipment regardless of whether they
receive general anesthesia or sedation. Airway management must be carefully
planned before the start of the procedure, particularly in patients with potentially
challenging airways or at risk of decompensation during the procedure. Esophageal
temperature monitoring is an important aspect of atrial fibrillation ablation to
decrease the risk of atrioesophageal fistula. Appropriate vascular access is
necessary, as patients may present with less frequent but life threatening
cardiovascular complications. Arterial monitoring at the time of induction or
coinciding with procedural vascular access should be used when appropriate. In
our institution, atrial fibrillation ablations are almost all performed under general
endotracheal anesthesia with non-invasive blood pressure monitoring. Conversely,
the choice of anesthetics for ventricular tachycardia ablation is made after
discussion between the proceduralist and anesthesiologist. These patients almost
all have arterial blood pressure monitoring to assess the stability of their
arrhythmia. However, controversy still exists regarding the potential for sedative
and anesthetic agents to suppress arrhythmia induction. For this reason, some
proceduralists wish to avoid general anesthesia until the mapping portion of the
procedure is completed. While experts differ widely on this subject, considerable
debate persists about who should provide different kinds of sedation and anesthetic
services in the EP lab.
Procedures in the Electrophysiology Lab
Device management from the Electrophysiology service frequently occurs in
the EP lab. Pacemakers and ICDs can be surgically implanted in this setting.
Endovascular lead placement is typically guided by fluoroscopy, and the generator
box is connected and tested before the incision is closed. In addition, patients
requiring exchange of an existed implanted generator can routinely be cared for in
this setting. Light sedation from a registered nurse and local anesthetic from the
interventionalist facilitate good surgical conditions. On occasion, defibrillator
testing is performed requiring brief periods of intensely deep sedation, which may
alter the mix of necessary anesthesia providers. Higher risk procedures such as lead
extractions are typically performed in the operating room, and in our institution,
only case-by-case exceptions are made to this.
Transcatheter EP studies and ablations are performed to target a variety of
conditions. In each, multiple venous sheaths are placed in the femoral veins for
positioning electrodes in the right atrium, right ventricle and in the area of the His
bundle. A multielectrode catheter may be placed in the coronary sinus. If left
atrium access is desired, a transseptal catheterization permits sheath placement
across the interatrial septum, as is necessary for AFib ablations. Retrograde
advancement from the arterial circulation permits access to the left ventricle, as is
sometimes necessary for VT ablations. Systemic anticoagulation is necessary while
the left heart is instrumented.
A diagnostic EP procedure follows. Programmed electrical stimulation of the
atrium or ventricle, sometimes during a catecholamine infusion, induces the
tachyarrhythmia and allows for further diagnosis. A number of mapping techniques
have been developed to help position the ablation electrode in the proper site.
These techniques include Activation Mapping, Pace Mapping, Entrainment Mapping,
Anatomic Localization, Electrogram Characteristics, Scar Mapping and a variety of
combined approaches. Activation Mapping is performed through the tip of an
ablation catheter to define the timing of electrical activation across regions of the
heart. The goal is to identify the endocardial site with the earliest activation, likely
the origin of a tachyarrhythmia. This may be employed in atrial tachycardia, WPW
or other reentrant nodal tachycardias. Pace Mapping involves pacing from the
ablation catheter during a sinus rhythm in an attempt to match QRS morphology on
the EKG with the QRS morphology during spontaneous tachycardia. This is used
most frequently during mapping of ventricular tachycardia. Entrainment Mapping
involves pacing from the ablation catheter at a paced rate slightly higher than the
tachycardia rate and evaluating the response of the tachycardia at the cessation of
pacing. This approach is used to identify sites that are within a reentrant circuit,
and is useful in the ablation of atrial tachycardias and atrial flutter. Anatomic
Localization approaches are used when the arrhythmia has a known anatomic
course, as is frequent in certain atrial flutters. Electrogram Characteristics are
frequently sought from the tip of the ablation catheter. This can be used to identify
the AV node, His bundle, right bundle, fascicular and accessory pathways, and this
modality is useful for ablation of the AV node and many types of VT. Scar Mapping
can be used when a patient cannot tolerate remaining in VT for sustained periods of
time during standard mapping. Instead, scar substrate can be mapped in sinus
rhythm by measuring voltage amplitude throughout the ventricle. Regions of low
voltage are associated with myocardial scar and can be targeted for disruption of
reentry circuits.
Ablation is typically done using radiofrequency waves, and small repetitive
lesions of approximately 8mm in diameter and 3-5mm deep are made in the
endocaridium. Saline irrigation at the tip of the catheter is used to prevent
dangerous rises in temperature. Cryoablation is a different technique which avoids
the high temperatures seen with RFA and can be used as an alternative with similar
efficacy and safety. Epicardial approaches through a subxiphoid catheter can be
used when endovascular approaches have been unsuccessful. After completion of
ablation, programmed stimulation is performed, frequently with a catecholamine
infusion, to try to reinduce the arrhythmia.
Many ablative procedures require an approach that combines anatomic
information and mapping techniques. In atrial fibrillation ablations, pulmonary vein
ostia are identified and sequentially isolated through mapping with a circular
multielectrode catheter, then electrical connections between the posterior left
atrium and pulmonary veins are ablated. Advances in the past ten years including
sophisticated three-dimensional mapping software and steerable ablation catheters
have increased the long-term success rate and freedom from recurrence with this
procedure. New data suggests that alterations in anesthetic technique to keep the
mediastinum free from movement during ablation may further increase long-term
success. Indeed, several authors are advocating use of high-frequency oscillatory
ventilation for this purpose. Further studies regarding this challenging and
controversial anesthetic technique are pending.
Anesthetic Implications and Complications of Procedures in the EP Lab
A host of anesthetic implications exist for procedures in the EP lab. Patients
frequently present with a host of comorbidities including coronary disease,
cardiomyopathy, limited functional capacity, obesity, and obstructive sleep apnea.
Procedural implications for consideration include appropriate airway control,
prevention of patient movement during mapping and ablation, mitigation of
hemodynamic effects of vasoactive drugs, management of hemodynamic
compromise from arrhythmia induction, and anticipation of catastrophic
complications.
Airway management is best performed in controlled circumstances.
Providing anesthesia in a remote location presents specific challenges, and securing
the airways is of particular concern, as the anesthesiologist must work with limited
resources and help. Non-anesthesia medical personnel in the EP lab may have little
knowledge of handling the airway or providing needed equipment. A conservative
approach is recommended.
Patient movement can be problematic during the procedure. Movement after
completion of mapping of recorded targets may make the map useless, making
general anesthesia attractive for long procedures. Use of neuromuscular blockade
during ablation is controversial and has both advantages and disadvantages. The
desire to prevent patient movement must be balanced against the risk of accidental
phrenic nerve stimulation and ablation.
Hemodynamic management can pose a particular challenge during
procedures. Patients presenting for treatment may be critically ill or in advanced
heart failure. Administering an anesthetic for these patients while maintaining
hemodynamic stability can be challenging. The ability of a patient to tolerate
arrhythmia may be impaired, especially in cases with cardiomyopathy and poor
ejection fraction. Vasoactive drugs, including isoproterenol and epinephrine, are
routinely used to maintain adequate cardiac output or blood pressure during the
procedure. Several case reports describe the use of mechanical support devices,
including Intraaortic Balloon Pump (IABP), Impella endovascular circulation assist,
Percutaneous left Ventricular Assist Device (pVAD) or veno-arterial extracorporeal
membrane oxygenation (VA-ECMO). No single support therapy has proven to be
superior to another, but all illustrate the potential benefits from invasive support in
the critically unstable patient requiring arrhythmia ablation.
Procedural complications may arise from injury to a variety of cardiovascular
structures. This includes injury to the femoral vessels, retroperitoneal hemorrhage
from IVC injury, heart block from inadvertent ablation of desired cardiac electrical
structures, cerebral embolic events, pulmonary venous stenosis, valvular structural
injury, phrenic nerve ablation, and cardiac perforation with either pericardial
tamponade or creation of atrioesophageal fistula. Cardiac tamponade from
perforation of the left atrium in the pericardial sac is one of the most common
reported complications of RFA for atrial fibrillation. Maintaining a high index of
suspicion for bleeding and tamponade is key to early diagnosis and effective
treatment. Pericardial collections of blood can frequently be imaged with
intracardiac echocardiography. Depending on the location of the perforation,
tamponade may be treated with pericardiocentesis and reversal of anticoagulation.
However, on occasion, emergent surgical exploration is necessary. Atrioesophageal
fistula is a very rare but dreaded complication of atrial fibrillation ablation.
Esophageal temperature monitoring with fluoroscopically guided placement has
been shown to decrease the incidence of AEF. These patients may present with
fever, mediastinitis, sepsis, hematemesis or stroke from intracardiac gastric air. A
high index of suspicion is required for proper diagnosis and surgical treatment.
Understanding anesthetic implications and managing the host of potential
complications associated with EP procedures requires a healthy respect from the
anesthesia provider during what may otherwise be long and uneventful procedures.
In this setting, the value of collaborative communication among all parties deserves
repeated emphasis. Providers from a variety of disciplines may have incomplete
understanding of each other’s skill sets, and institutional and cultural barriers to
bidirectional communication should be targeted for elimination. It is our opinion
that optimum medical outcomes exist when collaborators work actively to resolve
competing medical interests.