Moderate sedation/analgesia (“conscious sedation”)
Normal response to verbal stimulation
Purposeful** response to verbal or tactile stimulation
Purposeful** response following repeated or painful stimulation
Unarousable even with painful stimulus
No intervention required
Intervention may be required
Intervention often required
May be inadequate
May be impaired
The anesthesiologist’s presence is often requested if deep sedation and/or anesthesia are required; the guidelines set by the ASA indicate that the practitioner providing a specific level of sedation must be able to rescue the patient who inadvertently entered a deeper plane of sedation. For example, a practitioner administering moderate sedation must be able to recover the patient from deep sedation, while provider prescribing deep sedation must possess the skill level necessary for reversal of general anesthetic . Bubien, et.al, published a consensus of North American Society of Pacing and Electrophysiology (NASPE) endorsing the need for anesthesia service during deep sedation and general anesthesia . Additional guidelines related to provider’s qualification such as Advanced Cardiac Life Support training, certifications, scope of practice limitations, and the list of sedation drugs permissible for use by non-anesthesiologist staff are often generated within each institution.
Benefits and Tradeoffs of General Anesthesia
It has been recognized that scheduling ablation procedures with anesthesiology service providing the sedation or general anesthesia may result in the increased total cost of the procedure [3, 4]; this is likely the result of the direct anesthesiology service cost as well as the requirement for post-anesthesia recovery period in a specialized unit, potential scheduling delays while anesthesia turnover occurs, etc. These difficulties associated with anesthesia involvement have been contrasted with the great success of managing these cases with minimal and moderate sedation provided by a non-anesthesiologist [3, 4]; additionally, deep sedation with Propofol by a non-anesthesia provider is commonplace in Europe and has a great safety record . Therefore, involvement of the anesthesia service is only warranted if the demonstrable patient benefit exists, the procedure carries an elevated complication risk, or the patient is not able to tolerate sedation due to physical or psychosocial reasons. On the other hand, it was observed that during Atrial fibrillation (Afib) ablation employing general anesthesia, both the time of fluoroscopy and total procedure duration were significantly shorter while resulting in a higher cure rate of atrial fibrillation, thus potentially offsetting the implied cost of general anesthesia .
To further complicate the decision to proceed with general anesthesia, it was observed that patients undergoing ablation under general anesthesia had higher rate of thermal esophageal injury . However, in this particular study both sedation and general anesthesia groups exhibited zero incidence of atrioesophageal fistula formation and the injuries resolved spontaneously without any sequellae
Equipment and Monitoring
The American Society of Anesthesiologists extensively described the minimum monitoring requirements of the patients undergoing general anesthesia for a surgical procedure; this is applicable to ablation procedures performed under general anesthesia, as well as deep sedation and Monitored Anesthesia Care (MAC) .
Pulse oximetry is a rapid, quantitative, and reliable method of assessing patient’s oxygenation status. It employs transillumination of tissue, usually at the fingertip, earlobe, or nare with a minimum of two wavelengths of light, thus allowing resolution of oxyhemoglobin and deoxyhemoglobin concentrations. When coupled with a variable pitch audio output this monitor provides a continuous background information about both patient’s heart rate and blood oxygen concentration, and thus it is one of the essential monitors recommended by ASA during general anesthesia and deep sedation .
Ventilation monitoring during mechanical ventilation routinely consists of automatic tidal volumes, circuit integrity, and airway pressure monitoring by the circuitry of the anesthesia machine. Additionally, inhaled and exhaled gas spectroscopy reports fractions of inspired gases and volatile anesthetics in addition to producing a continuous capnography waveform . In the absence of invasive ventilation capnography remains a valuable tool for monitoring spontaneous ventilation as it allows for apnea detection much earlier than pulse oximetry alone.
Circulation is probably the most redundantly monitored vital sign as continuous EKG (electrocardiogram) and pulse oximetry provide information about patient’s heart rate. Additionally, multiple-lead EKG tracing is a valuable tool for detecting cardiac ischemia. Leads II and V5 are most commonly monitored and provide at least 80 % sensitivity for myocardial ischemia, while modern telemetry machines are capable of automatically monitoring five or more leads and will alert the provider should ST morphology change.
Non-invasive blood pressure (NIBP) is recommended by the ASA to be cycled at least every 5 min and is recommended even for patients in whom invasive blood pressure assessment is employed. NIBP is reliable and is not prone to calibration errors associated with pressure transducers. Also, arterial blood pressure is sometimes transduced via the shared sheath introducers which can be subject to thrombosis, malposition, or occlusion by the ablation device. Additionally, at the time of hemodynamic instability when dedicated BP reading is vital, these sheaths may need to be exchanged for an intraaortic balloon pump (IABP) or a peripheral arterial cardiopulmonary bypass (CPB) cannula.
Body temperature monitoring is required during ablations under general anesthesia, as these procedures routinely last greater than 30 min, and often exceed 3–6 h. Both passive and active rewarming measures should be employed pre-induction and should continue throughout the procedure; these include warm blankets, socks and head covers, forced air warming, fluid warmers, conservation of airway moisture, and other site-specific means to maintain normothermia.
Radiofrequency (RF) ablation of the posterior surface of the heart exposes the patient to the risk of thermal injury to the esophagus, which is implicated in the development of an atrio-esophageal fistula, a dreaded and serious complication of left atrial ablation. The esophageal temperature can be monitored using either a standard esophageal temperature probe, or a purpose-designed unit with multiple thermistors that measures esophageal temperature along the length of the left atrium. Usually these monitors are placed with fluoroscopic guidance to ensure optimal sensitivity . Once a pre-determined esophageal temperature is reached the ablation is paused or power to the ablation probe is reduced to mitigate the risk of injury. It is also worth mentioning that there is a unique potential for interference of radiofrequency used for ablation and esophageal monitoring probe. Deneke, et.al. hypothesized that thermal esophageal injury may occur in patients with esophageal temperature probes due to the probe acting as a receiver of the RF energy, which is then converted to heat; this pattern of esophageal ulceration was not seen in the unmonitored control cohort .
Transesophageal echocardiography (TEE), while not recommended as a routine monitoring modality in the operating room nor in the EP laboratory, has a unique application in the setting of atrial fibrillation. Given the prevalence of left atrial thrombus in approximately 10–15 % of patients with atrial fibrillation , and an estimated 3.5 fold increase in thromboembolic complications, TEE screening is commonly, though not universally  performed before ablation procedures or cardioversion. Patients who are treated with long-term anticoagulation are not completely protected from forming left atrial thrombi (LAT). In a very recent meta-analysis Di Minno, et al. demonstrated LAT incidence of 3.5 % in cohorts that were reported to be 100 % anticoagulated for atrial fibrillation. The overall safety of TEE needs a separate discussion with the patient, especially those with relative or absolute contraindications including esophageal or GI pathology, history of chest irradiation, or a risk of GI bleeding from varices . While the overall risk of esophageal perforation is reported to be 1:1000 or less , and while only a handful of reports have been generated on esophageal injury during ablation procedures , combined risk of esophageal damage from radiofrequency ablation and TEE probe manipulation have to be weighed carefully in a patient who is frail or otherwise predisposed to this complication.
Anesthetic Considerations: Preoperative Evaluation
As eluded above, general anesthesia is reserved for ablation procedures in which procedural challenges or patient-specific comorbidities may preclude successful completion of ablation with non-anesthetist administered sedation. Usually, this referral is initiated by the primary EP physician and thereafter is achieved through scheduling a pre-anesthesia assessment. Anesthesiologist who is performing the procedure is tasked with risk-stratifying the patient according to cardiac and pulmonary comorbidities, obesity and potential for obstructive sleep apnea (OSA), renal dysfunction, hematologic derangements, anticoagulation status, history of anesthetic problems in the past, allergies, and pertinent chronic medications.
Many ablation procedures require mapping of arrhythmogenic foci which is accomplished by inciting arrhythmias either chemically or electrically. These bouts of increased heart rate place additional strain on myocardial supply and demand balance, possibly exacerbating pre-existent coronary artery disease symptoms. Therefore, a thorough cardiac history and physical examination should be the center of pre-anesthesia evaluation.
Most recent guidelines published jointly by the ASA, AHA and ACC have simplified the risk stratification into 2 instead of 3 groups: Low risk of major adverse cardiac event (MACE) and intermediate or high risk of MACE. Procedures that require general anesthesia would commonly fall into latter category, and thus a reasonable functional status (>4 METs) must be documented, or a cardiovascular evaluation must be performed .
Anesthetic Considerations: Intraoperative Management
Selection of sedation strategy between monitored anesthesia care (MAC) or general anesthesia requires a discussion and agreement between the cardiologist and the anesthesiologist. Patient-specific comorbidities as described above and procedural factors such as the need for prolonged immobility, hybrid intracardial/epicardial ablation, and the need for invasive monitoring or TEE assessment will influence the decision to proceed with general anesthesia. The need for muscle relaxation to achieve absolute immobility will require placing an endotracheal tube, as opposed to maintaining the patient spontaneously ventilating with or without a Laryngeal Mask Airway (LMA). If a decision is made to secure the airway with an LMA, one must consider the difficulty reaching the patient’s airway once X-ray unit is moved into position and the undesirable loss of arrhythmia mapping if a patient is shifted during intubation in the middle of the procedure.
Patients with known difficult airway and patients with unfavorable airway exam may be better served with intubation at the beginning of the procedure using a combination of video laryngoscopy, fiberoptic bronchoscope, and optimal intubation positioning, etc. Fluoroscopy tables also lack familiar mobility and it may be difficult to elevate and flex the patient, or use reverse Trendelenburg positioning; an induction and intubation while patient is lying on a more flexible transport gurney may be a better option.