Ventricular tachycardia (VT) electrophysiologic study and ablation

Wilson Cui, MD PhD, Matt Dudley, MD

PROCEDURE 

Ventricular tachycardia (VT) electrophysiologic study and ablation

PATIENT DEMOGRAPHY

A heart rate greater than 100 beats per minute, with a wide QRS complex (> 120ms) is presumed to be VT until proven otherwise. While sustained VTs are usually life threatening, patients with nonsustained monomorphic VT (NSVT) are often asymptomatic and are diagnosed on routine ECG or other cardiac monitoring. Based on ECG, the cardiologist can usually determine whether the arrhythmia is truly VT or rather supraventricular tachycardia with aberrant conduction. The presence or absence of structural heart disease is the main determining factor whether the patient is at risk for developing sustained VT and sudden cardiac death (SCD). As such, patients scheduled for VT ablation can range from health young adults, to patients in end stage heart failure with left ventricular assist devices, and anything in between.

NSVT is usually self-limiting as it by definition should last no more than 30 seconds. During these episodes, palpitation, diaphoresis, dizziness or lightheadedness are common complaints. Less frequently there would be chest discomfort and shortness of breath. Rarely, syncope can occur in those with underlying heart disease and with a decrease in cardiac output. Ambulatory monitoring may determine whether the VT lasts longer, with more severe symptoms, which would carry worse prognosis. The prognosis of NSVT usually is benign in those without heart disease. In addition to underlying structural disease, polymorphic VT and prolonged QT interval are other risk factors for malignant rhythm and SCD. Beta blocker or calcium channel blocker can be used before other anti-arrhythmics are tried. Catheter-based ablation is an alternative to medical management, and some patients choose this invasive procedure. In order to localize the abnormal conducting tissue, the patient is instructed to stop anti-arrhythmia medication and/or beta-blocker a few days prior to the procedure.

DISEASE BACKGROUND AND PROCEDURAL DESCRIPTION

The incidence of NSVT in the general population is 0 to 4 percent. Some research suggests that NSVT may be a risk factor for future cardiac disease. On the other hand, the presence of structural heart disease increases the risk of NSVT, and other more concerning VTs such as sustained monomorphic VT and polymorphic VT. Structural heart diseases include: 

• Coronary artery disease and post-myocardium infarction (MI) scar 

• Non-ischemic dilated cardiomyopathy 

• Hypertrophic cardiomyopathy 

• Valvular diseases 

• Congenital cardiomyopathy


In many of these patients, they may already have ICDs for primary prevention of SCD. 


The formation of reentrant circuit is based on the differences in the electrophysiologic properties of the cardiomyocytes. In those with cardiac diseases, injured myocytes, fibrosis from previous infarction, ventricular dysfunction and remodeling, electrolyte imbalance (K, Mg etc) predispose the myocardium to VT. In the absence of structural disease, common types of NSVT include: 


• Right ventricular outflow tract (RVOT) tachycardia 

• Idiopathic left ventricular tachycardia 

• Long QT syndromes 

• Arrhythmogenic RV cardiomyopathy

The diagnostic procedure begins with venous access to bilateral femoral and/or right internal jugular (RIJ) veins. A total of four to five sheaths are placed. Then various recording and pacing electrode arrays on catheters are inserted into the heart. For left sided access, either a trans-septal approach via a pre-  existing patent Foramen Ovale (PFO) or a needle puncture through the interatrial septum, or retrograde approach via one of the femoral arteries is used. Each catheter has multiple electrodes along its tip capable of recording electrogram with the exception that the most distal electrode can also stimulate and pace. Catheters are guided with fluoroscopy, intracardiac echocardiography, and with the assistance of various mapping systems that help locate the ectopic foci, identify the depolarization pattern, position the ablation catheter, and evaluate ablation results. The ablation of ectopic foci and pathways of cardiac tissue is performed most commonly with radiofrequency (microwave) energy to induce a transmural heat injury (60 to 70 degree Celsius at the catheter tip), which scars to isolate the electrical propagation of impulses. The tip is actively cooled with saline irrigation to avoid over-heating and the undesirable formation of coagulum. Coagulum prevents effective tissue lesion, and the catheter needs to be withdrawn to remove the coagulum. Other methods include cryoablation via catheter or balloon and laser ablation via balloon.

It is thought that any sedation that suppresses the endogenous catecholamine release may decrease the frequency of arrhythmia, and make the mapping of the pathway and thus ablation more difficult. It would be ideal to minimize the amount of sedation the patient receives during mapping.

PRE-OPERATIVE ASSESSMENT 

• Standard ASA NPO guidelines should be followed for this elective procedure. 

• A thorough assessment of the patient’s airway and respiratory status is essential since the airway will be far from the anesthesia provider with potential obstacles such as the fluoroscopic equipment and drapes. History of reactive airway disease, COPD, OSA, GERD, pleural effusion, or pulmonary edema from acute heart failure may affect the anesthetic management. 

• In addition to the arrhythmia, the overall cardiovascular and functional status of the patient should be assessed. While some patients who have NSVT without associated underlying structural heart disease, many other do, and they tend to be older and diseases are diagnosed with additional cardiac evaluation such as echocardiography, stress test or other cardiac imaging. 

• Anti-platelet agents and anticoagulants use should be noted, though it is rare in this population. Anti- platelet agents are usually not stopped. Warfarin is usually not stopped as long as patient has been on chronic, stable, therapeutic dose. Other agents are stopped at the proceduralist’s discretion. Regardless, this may increase the risk of bleeding or hematoma during and after the procedure, by anesthesia and the proceduralist. 

• Patient with chronic renal insufficiency or end-stage renal disease will need to have their electrolytes and fluid status assessed carefully. The team should be mindful of exposure to nephrotoxic contrast agents in patients with reduced GFR; however, EP stuides do not commonly expose the patient to contrast. 

• Patients who suffer from chronic back or leg pain may not tolerate spending extended periods in a supine position without proper positioning, padding and analgesia. 

• It is important to set proper expectation for the patient, who may say “just put me to sleep.” As most VT ablations at UCSF are done under MAC, the patient should expect to be awake once mapping starts.

PRE-OPERATIVE PREPARATION 

• Routine checks of anesthesia machine, emergency airway equipment, suction and resuscitation 
medications are imperative because access to additional equipment and anesthesia providers are limited. Usually, two infusion pumps and an invasive pressure transducer are available in each lab. At UCSF, a video laryngoscope (Glidescope) is located outside the EP control room. Contact the off-site anesthesia technician if you need any additional equipment. 

• Blood products are usually not required, but a blood type and antibody screen should be current. 

• Antibiotic is not indicated for this percutaneous procedure. 


ACCESS/FLUIDS 


• At UCSF, the EP nurse will start a peripheral IV in the pre-op holding, usually 18 or 20 gauge (left arm). 

• Sometimes for VT study/ablation, a RIJ sheath is placed by the proceduralist for CS cannulation. 

• Additional PIV is usually not necessary. Remember that the introducer sheaths may be used for central venous access. Sometimes, when a heparin infusion is necessary (left sided ablation), the EP team would use the right IJ sheath so the EP nurse can draw ACT samples from the femoral sheath without 
contamination. In the absence of RIJ access, the heparin can be infused through the PIV (some anesthesia providers prefer a separate PIV).
• Anticipated blood loss is minimum, usually associated with initial access and flushing of the sheaths. 

• Continuous irrigation of ablation catheters (1 to 2 L total) and sheath (30 mL/hour each), may add 
significant volume and may prompt diuretic use at request of the proceduralist. 


MONITORS 

• Standard ASA monitors: The EP staff will assist you in placing radiolucent ECG leads to ensure that they 
do not interfere with the fluoroscopic images or the rest of electrophysiology monitors. Sometimes, the anesthesia ECG leads can be connected to the mapping system directly. 

• Invasive arterial monitor is not required; however, it can be useful and is recommended in those patients who have a history of structural heart disease, low ejection fraction and may not tolerate rapid pacing/heart rate. If an arterial (femoral) sheath is placed for left sided ablation (retrograde approach), pressure can be transduced from the sheath and monitored by anesthesia. 

• Temperature should be monitored as the procedure can be lengthy. An axillary probe is sufficient for patients not under general anesthesia. A lower body forced air warmer is used. 

• Discuss with the EP team regard the need for urinary bladder catheter, but is highly recommended as the procedure can be lengthy. A condom catheter may be an alternative for a male patient

ANESTHETIC TECHNIQUES 

• Anxiolytic premedication should not be given routinely in the holding area as most ambulating patients 
are expected to walk into the EP lab and sit up-right on the table while monitors and patches are placed. 

• Broncho-dilator, anti-reflux medication and antacid should be given as indicated by the anesthetic technique and the patient’s co-morbidities. 

• Majority of catheter ablations for VT at UCSF are performed under MAC and is preferred by the EP team. The anesthetic goal is to provide analgesia during the initial painful portion of the procedure (Foley and vascular access) and to ensure both patient safety and patient cooperation thereafter that will maximize the chance for a successful study. The most stimulating portion of the study is in the beginning. Your anesthetic may range from a detailed pre-operative discussion, verbal reassurance, generous local anesthesia supplemented with minimal sedation in a motivated patient, to deep sedation in a less cooperative patient who has a reassuring airway. Common pharmacological options include: 1) midazolam and fentanyl; 2) propofol infusion with intermittent fentanyl bolus; 3) Remifentanil infusion (in selected population). 

• Little to no sedation is preferred during the mapping portion of the study. With the exception of remifentanil in pediatric population, there is scant evidence on the effect of various anesthetic on the inducibility of tachyarrhythmia. Nonetheless, one tries to minimize any sedative medication as long as the patient is comfortable enough to remain cooperative. One should consider IV acetaminophen early in the procedure especially in MAC cases. 

• Vasoconstrictor or inotrope infusions may be needed to support patients with low EF during tachycardia or rapid pacing
• Once the initial electrophysiological study is completed the sedation may be deepened for the subsequent ablation, even GA perhaps. Always communicate with the EP team regarding the necessity or permissibility of deeper sedation. 

• Supplemental oxygen can be provided with nasal cannula with CO2 monitoring. Alternatives include oral/nasal airway, simple face mask, non-rebreather, or anesthesia mask with straps to provide PEEP (it is time to reassess your “MAC”). 

• The emergence should be straight forward, which involves discontinuing the sedation and monitoring for any airway obstruction before leaving the EP lab. The EP staff will remove the sheaths, hold pressure for at least 15 minutes, and they prefer a relatively cooperative patient. 

• Recovery of a patient after general anesthesia will be in the 4th floor PACU, while the patient who had MAC will be recovered in the EP holding room unless the anesthesia provider felt that a higher level of care (PACU or ICU) is necessary due to co-morbidities or intra-operative events, or if the length of recovery is expected to exceed the hours of EP staff. The patient will need to keep the legs unflexed for at least 4 to 6 hours to minimize the risk of bleeding. 


KEY PROCEDURE-RELATED POINTS

• Those patients referred to tertiary medical centers such as UCSF may have had recurrent arrhythmias and prior ablations. The subsequent study/ablation procedure may be time-consuming. 

• Access is primarily through sheaths placed in the femoral veins and RIJ sheath for a CS catheter, which are usually placed by the proceduralist. Local anesthetic is used even for patients under GA. This is performed by the EP fellow, usually prior to attending time out. 

• Pre-procedural transthoracic echocardiogram may be necessary in patients with end stage systolic heart failure with dilated LV to rule out LV thrombus. Alternatively, TEE can be used, which has better sensitivity to detect LA thrombus. 

• **If left sided study is necessary, heparinization is required to reduce the risk of thromboembolism from left side catheters. The anesthesia provider will be asked to give heparin boluses, while the EP staff will manage the infusion and check ACT. If transseptal puncture is performed, extreme caution should be used to avoid venous air and paradoxical embolism. 

• Hemodynamic fluctuation is often seen, usually associated with induced tachycardia and pacing. While some patients may tolerate the prolonged tachycardia, many patients with structured heart diseases may not. Frequent BP measurements or invasive arterial pressure may be necessary. 

• Infusion of isoproterenol, a non-selective beta agonist with chronotropic, dromotropic, inotropic and vasodilatory effects, is commonly used for elicit/evaluate tachyarrythmias and is administered by the EP nurse. Phenylephrine infusion may be needed to counteract the vasodiation. 


POTENTIAL COMPLICATIONS 


• Arrhythmia that is hemodynamically significant is always a risk. Unstable VT will require defibrillation, and a deeper plan of anesthesia is needed.
• Vascular complications at the access site are not uncommon and range from self-limited site hematoma to retroperitoneal bleeding requiring urgent/emergent vascular surgery interventions. Resuscitation with fluids, blood products, and vasoactive medications may be necessary. 

• Cardiac perforation may occur due to catheter manipulation, during Trans-septal puncture or as a result of ablation. This may result in pericardial effusion, and potentially causing tamponade. This is usually indicated by persistent hemodynamic instability unrelated to the induced arrhythmia and refractory to routine vasoconstrictors and fluid. The EP team should be informed when this is suspected. Blood products should be ordered immediately. Consider reversing anticoagulation in consultation with the proceduralist. One or more of the femoral sheaths can be used for volume resuscitation. The management varies: 

  • “Wait-and-watch” approach when the effusion is small and self-limiting,
  • Emergent pericardial drain placement,

  • Rapid mobilization for surgical decompression of the tamponade.
• Stroke is possible due to the risk of thromboembolism with left sided catheters or in patients with PFOs. 
• Aortic perforation is a relatively rare complication that can occur during trans-septal puncture or 
retrograde catheter. 

SPECIAL ERGONOMIC CONSIDERATIONS 

• Extensions on breathing circuit, oxygen supply, IV tubing, and infusion tubing are necessary to allow the 
unobstructed movement of the fluoroscopy equipment. Consider consolidating and securing monitors, circuits, and tubing such that they clear the C-arm, biplane and avoid tangling. Tourniquets and blue clamps are often useful. The patient’s arms will be secured, padded and tucked, limiting our access. One should consider attaching two pre-flushed infusion lines that can be used for anesthetic agents such as propofol or remifentanil, and vasoactive agents. 
• Hazards to the anesthesia provider
• Equipment is in motion
• Be aware of the c-arm when it is in motion as it can move quickly and endanger heads and shins and may snag loose wires and tubings.
• Ionizing radiation

• Consider time (limiting exposure), distance (inverse square law), and shielding (both garments and barriers) when in ionizing radiation environments. Particular attention should be granted to protecting the lens of the eye, thyroid, hematopoietic centers in long bones, and reproductive organs as these are particularly sensitive to ionizing radiation. The exposure is greatest as it exits the collimator (the part below the table) in path to the image intensifier (the part above the patient). However, scatter radiation is produced as the X ray encounters items in its path (the patient). Areas on the body that are often overlooked (“weak spots”) include neck, shoulder/arm pits, and back. Lead (radiation protective) garments should cover the neck to the knees and are designed to be worn when facing the source.
• Magnetic fields

• At UCSF, one of the EP rooms (EP1) is equipped with the Siemens Stereotaxis NIOBE® magnetic navigation system that can be used to manipulate wires and catheters in the patient’s body. The magnets are material and cannot be turned off, but the magnetic field is tempered when in the stored position. The magnetic field is not on par with the electromagnet used in MRI; however, MRI precautions are recommended.  
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DURATION 4 - 8 

REFERENCES

Francis GS. Development of arrhythmias in the patient with congestive heart failure: pathophysiology, prevalence and prognosis. Am J Cardiol. 1986;57(3):3B-7B.

Kinder C, Tamburro P, Kopp D, Kall J, Olshansky B, Wilber D. The clinical significance of nonsustained ventricular tachycardia: current perspectives. Pacing Clin Electrophysiol. 1994;17(4 Pt 1):637-64.

Kwak J. Anesthesia for electrophysiology studies and catheter ablations. Semin Cardiothorac Vasc Anesth. 2013;17(3):195-202.

Price A, Santucci P. Electrophysiology procedures: weighing the factors affecting choice of anesthesia. Semin Cardiothorac Vasc Anesth. 2013;17(3):203-11.

Zipes DP, Camm A, Borggrefe M, et al. ACC/AHA/ESC 2006 Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death—Executive Summary: A Report of the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death). J Am Coll Cardiol. 2006;48(5):1064-1108.

Anderson R, Harukuni I, Sera V. Anesthetic considerations for electrophysiologic procedures. Anesthesiol Clin. 2013;31(2):479-89.