Blog with interesting cases and/or problems related to anesthesia with discussion based on best evidence in the literature.

February 1, 2018

WPW syndrome in patient with significant intraoperative hyperthermia

Recently I relieved one of our CRNAs. The patient was undergoing a marathon thyroidectomy which had started at 9:30 that morning. It was now 3pm.  The report I received indicated that the patient had developed hyperthermia with a  temperature (esophageal) of 38.8 C. The patient was receiving sevoflurane in oxygen and the HR was 110's.  BP was stable, and etCO2 was 36 mmHg with a minute ventilation of close to 5 to 6 L/min.  

I immediately verified that the room temperature was turned down and that the bear hugger was blowing cool air.

The main considerations when confronted with sudden intraoperative hyperthermia are:
  • malignant hyperthermia
    • in this case ruled out by normal minute ventilation and etPCO2, and lack of muscle rigidity.
  • Thyroid Storm
    • A possibility in this case, considering that the patient was having a thyroidectomy that required nearly seven hours of surgery. 
    • often causes tachycardia, hyperthermia, hyper or hypotension, hypokalemia and significant mental status changes that would not be evident until emergence.
  • cocaine abuse
    • excessive preoperative use can result in hyperpyrexia along with other symptoms like tachycardia, seizures, tachypnea, and dysrhythmias can often mimic MH.
  • sepsis
    • usually clinical history can clue in to this cause as well as tachycardia and hypotension.
  • pheochromocytoma
    • clinical history of headaches, sudden onset hypertension and tachycardia will lead the clinician to suspect this diagnosis
    • Catecholamine excess usually results in significant tachycardia and hypertension intraoperatively, but hyperthermia may also be present.
  • excessive medication administration
    • ketamine, atropine, dopamine, droperidol, or tricyclics 
  • Neuroleptic malignant syndrome (NMS)
    • from central dopaminergic blockade
    • butyrophenones, phenothiazines, metoclopramide, lithium,  tricyclics, monoamine oxidase inhibitors, selective serotonin  reuptake inhibitors, and haloperidol.
    • clinical symptoms similar to MH; tachycardia, hyperthermia, metabolic acidosis, and increased muscle tone.
    • The only possible way to distinguish NMS  from MH is that severe hypercapnia is not seen with NMS.
This patient also was diagnosed with Wolf Parkinson White (WPW) syndrome and was currently tachycardic.  WPW is a pre excitation syndrome where atrial cardiac impulses may bypass the AV node via Kent's bundle which can lead to pre excitation of the ventricle leading two main arrythmias: parosxymal supraventricular tachycardia (PSVT) or atrial fibrillation (AF). The accessory pathway (Kent's bundle) utilizes a sodium-dependent fast inward current for electrical impulse transmission, thus conducting signals more quickly from the atrium to the ventricle than the AV node, where a calcium-dependent slow inward current slows conduction.  Therefore, the general goal is to increase the refractory period of the bundle of kent relative to the AV node. However, conduction of cardiac impulses may travel in either a retrograde or anterograde direction through the bundle of Kent creating a clinical challenge in both diagnosis and proper treatment of pathologic tachycardias in patients with WPW syndrome. In some cases The bundle of kent  conducts impulses in only a retrograde direction as seen below in the graphic. In this case, no delta wave is visible on a normal EKG.
However, the vast majority of WPW patients can experience both anterograde and retrograde conduction via the accessory pathway. This is important because the EKG appearance is altered by the direction of conduction of cardiac impulses through the accessory pathway.  Patients with WPW syndrome who develop PSVT will have a regular R to R interval and may have a narrow complex tachycardia.  However, Antidromic AVRT can lead to wide complex tachycardia that is very difficult to differentiate from ventricular tachycarida (VT).  Antidromic AVRT is rare (~5% of PSVT in WPW).  Orthodromic AVRT is more common and results in a narrow complex tachycardia (200 to 300 bpm).  Patients with WPW syndrome and AF have an irregularly irregular wide complex tachycardia. (see graphic of AF in WPW below).
Therefore, the approach to a patient who develops pathologic tachycardia and has WPW syndrome in the preoperative period requires determining most importantly whether there is a regular R to R interval (see discussion below). In many cases, amiodarone is the preferred for treatment of pathologic tachycardia in WPW only because amiodarone can be safely used regardless of the etiology, i.e. AF, VT, PSVT.  If a clear diagnosis is possible from the cardiac tracing or 12 lead EKG, then a more selective medication may be chosen. For example, it may be best to begin treatment of PSVT  with vagal maneuvers if the patient is otherwise stable. These include valsalva, gag reflex (fingers in throat), or ice on face (diving reflex).  If prompt attempts at vagal maneuvers fail, then medications that can abruptly prolong the refractory period of the AV node (PSVT) such as adenosine 3 to 12 mg IV, verapamil 2.5 to 10 mg IV,  or esmolol 50 to 100 mg IV can be tried. It should be noted that several case reports of WPW syndrome patients receiving general anesthesia have commented on the use of lidocaine to prevent re entrant tachycardia.  It is unlikely that lidocaine will play a significant role in preventing re entrant tachycaridias in this patient population as noted in a paper published by Barrett et al. [2] In another study, the authors showed that in patients with WPW syndrome in A Fib with RVR, lidocaine was likely to increase (make worse) the ventricular rate, or have no beneficial effect [3]. Lidocaine is a class IB anti arrhythmic (blocks Na+ channels), but unlike procainamide (used in WPW syndrome with A fib), lidocaine decreases the effective refractory period (procainamide class IA increases the effective refractory period). Therefore, lidocaine based on its pharmacology alone would be predicted to be less useful in treating supra ventricular tachycardias as compared to procainamide. In the case of WPW with AF, the goal is exactly the opposite of that in a non WPW syndrome patient with AF. i.e. the goal in non WPW A fib is to slow conduction through the AV node, via medications such as verapamil.  In WPW AF, verapamil (and digitalis), which slows AV node conduction, is strictly contraindicated. Procainamide, on the other hand,  can be used since it prolongs the refractory period of the accessory pathway. In daily clinical practice, procainamide may not be readily available.   Amiodarone is a class III anti arryhmic and indeed can treat AF in WPW.  However, a  2010 review [4] found several studies that were able to identify a small risk of ventricular fibrillation (similar to the concern when using lidocaine for AF in WPW syndrome).  The study, therefore, concluded that amiodarone was not superior to procainamide in rate control for WPW with AF and could be dangerous.
  In any patient who becomes unstable due to the arrhythmia, synchronized cardioversion is the treatment of choice.   Opioids like fentanyl, benzodiazepines including midazolam have been found to have no effect on the EP effects of the accessory pathway. There is a case report of disappearance of delta wave after propofol administration making it the induction drug of choice if GETA is required [1]. Both isoflorane and sevoflorane do not have any effect on AV node conduction, however, desflurane if given at greater than a 6% concentration initially can lead to increased sympathetic output.  Therefore, if desflurance is chosen, slowly increasing the concentration would be required. 

Typically, the anesthetic management of a patient with WPW calls for the avoidance of increased sympathetic activity (pain, anxiety, fear, stress response from any cause, lighter planes of anesthesia, hypovolemia and the avoidance of anticholinergic medications.  Since the avoidance of lighter planes of anesthesia is critical in these cases, monitoring anesthesia depth with a BIS monitor would not be unreasonable in any patient with WPW syndrome who has not had the accessory pathway ablated.  

In this patient who was at risk for thyroid storm having a prolonged thyroidectomy surgery, significant hyperthermia with sinus tachycardia and WPW syndrome, presumptive treatment for thyroid storm was reasonable.  It turns out that many of the indicated treatments for a patient with possible thyrotoxicosis are also indicated to modify the risk in a patient having surgery with WPW syndrome.  An esmolol infusion is recommended to control HR in thyroid storm [5], and is not a bad choice to control HR and attenuate the sympathetic nervous syndrome in a WPW syndrome patient.  Also recommended for patients suspected of thyroid storm and persistent hypotension is cortisol IV (100 to 200 mg).  Decadron may inhibit the conversion of T4 to T3 (T3 is the main culprit in promoting symptomatology in thyrotoxicosis) [5]. 

In the end, the patient was extubated and taken to PACU.  Despite efforts to cool the patient, the temperature was still elevated in the PACU.  Fortunately, other than hyperthermia, the patient suffered no apparent ill effect from the surgery and recovered without sequelae.  However, vigilance and the ability to prioritize treatments in patients who present with two or more conditions simultaneously in the OR requires a more intimate understanding of the underlying goals at a mechanistic level.  In this case, the treatments recommended were beneficial for both conditions.

1. 8. Seki S, Ichimiya T, Tsuchida H, Namiki A. A case of normalization of Wolff-Parkinson-White syndrome conduction during propofol anaesthesia. Anesthesiology. 1999;90:1779–81.
2. Barrett PA, Laks MM, Mandel WJ, Yamaguchi I. Am Heart J. 1980. Jul;100(1):23-33.
3. Akhtar M, Gilbert CJ, and Shenasa M. Circulation 1981. Vol. 63(2):435-441.
4. Simonian SM, Lotfipour S, wall C, and Langdorf MI.  Intern Emerg Med. 2010, 5(5): 421-6.
5. Stoelting RK. Anesthesia and Co Existing Disease. p. 349

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