Supraventricular tachycardia (SVT) electrophysiologic study and ablation

Matt Dudley, MD, Wilson Cui, MD PhD   

PSVT Draft, 8/2014 

PROCEDURE

Supraventricular tachycardia (SVT) electrophysiologic study and ablation

PATIENT DEMOGRAPHY

Paroxysmal supraventricular tachycardia (PSVT) is defined as a heart rate greater than 100 beats per minute, usually with a narrow QRS complex (< 120ms) and has a regular R-R interval. In other words, it would be more accurately called regular narrow complex tachyarrhythmia. It has acute onset and termination and do not originate in the ventricles. While atrial fibrillation (AF) is technically a type of this group of tachyarrhythmias, AF ablation is discussed separately.

Narrow complex tachycardia can occur in patients of all ages. The overall incidence is 35 cases per 100,000 person-years. While the typical patient is relatively young, otherwise healthy, the tachycardic episodes, though infrequent, can be quite psychologically or physically debilitating. The most common complaint would be palpitation and diaphoresis with associated symptoms of dizziness or lightheadedness. Less common would be chest discomfort or shortness of breath. Rarely syncope, usually in those who have underlying cardiac disease, is reported. Although life style changes (avoidance of caffeine, nicotine, alcohol and other stimulants) and anti-arrhythmia medication can be effective in many patients, some cannot tolerate the side effect of medication and/or are refractory to pharmacologic treatments. The patient has been informed of the risks and benefits of catheter-based ablation, as an alternative to medical management, and has chosen to proceed with 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

Besides AF, other causes of regular narrow complex tachycardia include sinus tachycardia, atrial flutter, atrio-ventricular nodal reentrant tachycardia (AVNRT), atrio-ventricular reciprocating tachycardia (AVRT), (focal) atrial tachycardia, multifocal atrial tachycardia (MAT), sino-atrial nodal reentrant (SANRT), and other reentrant or junctional tachycardias. Reentry pathways such as those in AVNRT and AVRT are by far the most common causes, making up 60% and 30% of the cases respectively. Re-entry circuits arise from competing pathways (cardiac tissue) with differences in conduction velocity and refractory period such that a recurrent ectopic circuit (depolarization loop) is triggered and sustained, causing repeated depolarization of the ventricles via the His-Purkinje system. Other PSVT is caused by increased automaticity of the cardiac tissue.

In AVNRT, the reentry circuit is contained entirely within the AV node (functionally speaking). The reentry circuit is usually in the right atrium (RA) and behaves like atrial tissue. Of the two pathways, the slow pathway is usually the target of ablation, commonly runs posterior to the tricuspid annulus and anterior to the coronary sinus (CS) ostium. The ablation can be guided by electrogram, or less commonly, based on anatomy only. In AVRT, the reentry circuit consists of the AV node (normal pathway) and an accessory pathway. The accessory pathway connects the right ventricle and the RA, is contained within the atrio- ventricular (AV) groove, and behaves like ventricular tissue. AVRT can conduct in either direction- orthodromic (with electric impulse entering the ventricle via the AV node) or antidromic (via the accessory pathway). Right sided accessory pathways are usually located along the tricuspid annulus or the CS ostium from the inferior vena cava. Left sided pathways can be located and ablated by a catheter either in the left atrium/ventricle (via transseptal/retrograde approaches) or within the CS, which runs along the left AV groove.

Wolff-Parkinson-White (WPW) is a subtype of AVRT with a characteristic delta pre-excitation wave pattern on ECG that is common in younger adults. WPW pattern occurs in about 1 to 3 per 1,000 persons in the general population, but the prevalence is higher in first-degree relatives. It is more common in men than women, and men have a higher incidence of multiple accessory pathways. WPW may also be associated with congenital defects within the heart such as Ebstein’s anomaly.

Since these pathways can usually be located by catheters in the RA, venous access is typically sufficient. 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. Ablation catheters are typically introduced into the RA from the femoral vein up the iliac vein and vena cava. 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. Rarely, left atrial access, via a pre-existing patent Foramen Ovale (PFO) or via a trans- septal puncture, is required.

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. The patient may range from an elite athlete to someone who is frail from chronic de- conditioning, have reduced ventricular function due to tachycardia-induced cardiomyopathy, or have other structural heart diseases. It is important to note the patient’s symptoms during SVT episodes, which may range from asymptomatic to syncope, with the latter especially concerning. 

  • Anti-platelet agents and anticoagulants use should be noted, though it is rare in this population. 

  • 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 studies 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 SVT 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). 

  • Most patients having a SVT study/ablation will have a RIJ sheath 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 significant symptoms, such as syncope, or have a history of ischemic heart disease or cardiomyopathy 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, depending on the expected length of the procedure. 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. 

  • Vast majority of catheter ablations for PSVT 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. 

  • 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 


  • A complete EP study is performed to identify etiology of SVT, which may have multiple etiologies (e.g. AF and AVNRT). 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. 

  • Ablations for SVT commonly only require right heart access. However, AVRT may include accessory pathways adjacent to the tricuspid and/or mitral annuli, and this may require left atrial catheterization. If left sided study is necessary, heparinization is required to reduce the risk of thromboembolism from the left side catheters. The anesthesia provider will be asked to give heparin boluses, while the EP staff will manage the infusion and check ACT. Extreme caution should be used to avoid venous air and paradoxical embolism. 

  • Hemodynamic fluctuation is often seen, usually associated with tachy- or brady-cardia, and pacing. The changes are often self-limiting, but may require treatment. 

  • 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. 


POTENTIAL COMPLICATIONS 


  • Arrhythmia that is hemodynamically significant is always a risk. Iatrogenic complete heart block, 
previously used therapeutically, is a possible risk with ablation adjacent to the AV node and bundle of His. 

  • 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.
  • Esophageal injury or atrial-esophageal fistula is less common in right sided ablation, but still possible and catastrophic when it occurs. 

  • 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 with a 
specialized needle (Brockenbrough) and the advancement of trans-septal sheath (Mullins). 


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. 

DURATION 4 - 6 hours

REFERENCES

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

Blomström-Lundqvist C, Scheinman MM, et al.; European Society of Cardiology Committee, NASPE-Heart Rhythm Society. ACC/AHA/ESC guidelines for the management of patients with supraventricular arrhythmias--executive summary. a report of the American college of cardiology/American heart association task force on practice guidelines and the European society of cardiology committee for practice guidelines (writing committee to develop guidelines for the management of patients with supraventricular arrhythmias) developed in collaboration with NASPE-Heart Rhythm Society. J Am Coll Cardiol. 2003 Oct 15;42(8):1493-531.

Kobza R, Toggweiler S, Dillier R, Abächerli R, Cuculi F, Frey F, Schmid JJ, Erne P. Prevalence of preexcitation in a young population of male Swiss conscripts. Pacing Clin Electrophysiol. 2011;34(8):949.

Krahn AD, Manfreda J, Tate RB, Mathewson FA, Cuddy TE. The natural history of electrocardiographic preexcitation in men. The Manitoba Follow-up Study. Ann Intern Med. 1992;116(6):456.

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

OrejarenaLA,VidailletH,DeStefanoF,MordstromDL,VierkantRA,SmithPN,HayesJJ. Paroxysmal supraventricular tachycardia in the general population. J Am Coll Cardiol. 1998;31(1):150.

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

Trohman RG. Supraventricular tachycardia: implications for the intensivist. Crit Care Med. 2000;28(10 Suppl):N129.

 

 

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This information is meant to serve as an educational resource. Clinicians should use their own professional judgment in the care of any individual patient as the guidance contained in this document may not be appropriate for all patients or all situations.