Emergency Medicine Forum

A nurse grabbed me to see a patient who needed to be seen immediately.

As I walked into the room, I saw an anxious young female (37 year old), holding her chest, tears in her eyes, and diaphoretic.  A quick look at the monitor and it was clear why.  The monitor revealed a narrow complex, rapid heart rate at 190.  On closer inspection, it was regular.  Her blood pressure displayed 110/60.  EKG confirmed narrow complex regular rhythm tachycardia, with st depression (3 mm) in the lateral leads. 

I quickly found out that she was not having chest pain, just felt very ‘uncomfortable’ in her chest as the rapid heartbeat scared her. She had experienced this about once a year for the past 10 years, but each time she could stop it by holding her breath and bearing down.  She did feel short of breath.  Quick exam revealed no rales, equal breath sounds, and no murmurs appreciated.

Questions:

1. What are the two most common causes of paroxysmal supraventricular tachycardia (PSVT)?

The two most common causes are AV Nodal Re-entrant Tachycardia (AVNRT) and AV Re-entrant Tachycardia (AVRT). 

AVNRT is more common and is diagnosed in 50-60% of patients with a regular narrow QRS tachycardia. (1)  AVNRT is more common in women, and usually occurs in younger individuals without structural heart disease. (1)  In most normal individuals, the AV node has only one conducting path, but in AVNRT patients, there is a second pathway in the AV node. The second pathway usually has a different conduction rate, and a different refractory period.  This type of assessor pathway is different from AVRT as it does not involve ventricular tissue, it all occurs in the AV node.

AVRT is the second most common cause of PSVT.  It is more common in males (male to female ratio of 2:1) (1). In this condition, there is an accessory pathway (sometimes called bypass tract) with errant strands of myocardium that bridge the mitral or tricuspid valves. (1)  These connections are the result of anomalous embryonic development of myocardial tissue bridging the usual fibrous tissue that separates the ventricle and the atrium. (2)  In this condition, the conduction can occur normally through the AV node, then back up to the atrium through the accessory pathway (orthodromic (0=ordinary conduction through AV node…that’s how I remember it)) or the conduction can start in the accessory pathway and then go backwards through the AV node (antidromic).  When it starts in the accessory pathway (antidromic=abnormal QRS, again how I remember it), the ventricle is not depolarized through the bundle of His, and therefore the QRS is wide. 

Wolf-Parkinson-White (WPW) syndrome is a AVRT conduction abnormality.(1)  In addition to PSVT, WPW patients can also develop atrial fibrillation and atrial flutter.   You can sometimes identify WPW  based on the delta wave (slurring of the upstroke of the QRS) and a shortened PR interval on EKG. (1)

2. What are the side effects of Adenosine?  When is it relatively contraindicated?

Typical adverse side effects of Adenosine include flushing, chest pain, and dizziness.  (1)  I always warn patients about the strange feeling they may have when they convert.  I never tell them they will feel like they may die (although some Doctors must tell people this as I’ve had several patients relay this to me).  I usually explain the heart rate goes from very fast to very slow (I don’t tell them it goes to 0!), and the rapid change is kind of like putting the brakes on very quickly, it will give them strange feelings in their chest.  But, the medicine only lasts a few seconds, so even if the feeling is uncomfortable, it will go away very quickly.

Adenosine is contraindicated in heart transplant patients (2), and should be used with caution in patients with severe bronchospasm. A recent Best Bets review found little evidence on the adverse effects of IV adenosine in patients with a history of bronchospasm.(3) They did find 4 case reports of bronchosmasm induced because of the adenosine. (3)  Many references also describe caution in patients with wide complex tachycardia, but a relative recent study (2009) was a retrospective study of 197 patients (116 with SVT, and 81 with Ventricular Tachycardia (VT)), and found no adverse effects (0/81) from the use of adenosine in patients ultimately found to have VT. (4)  The authors also noted that patients without a response to adenosine were 9 times more likely to have VT. (4)  For patients with PSVT, 90% will convert with a 12 mg dose of adenosine.(1)

Outcome: 
The nurses quickly attempted IV, drew up some Adenosine, and obtained an EKG which confirmed SVT.  I coaxed her through some vagal attempts, but no success.  There was difficultly getting IV access, so we laid her down to get an EJ.  When we had her hold her breath and bear down (vagal again), she converted spontaneously.  Then she explained she did not want the medicine that would cause her to die for a second. 

Ultimately, her labs including electrolytes were fine, the rate related ischemia on her EKG normalized with conversion to sinus rhythm, and after discussion with cardiology, she was discharged to follow up with them tomorrow.

Note the delta waves on this EKG of a patient with WPW

References:

1. Gugneja M. Kraft PL.  Paroxysmal Supraventricular Tachycardia.  Emedicine. Sept 28, 2010.  Accessed at:  http://emedicine.medscape.com/article/156670-overview
2. Hemingway TJ, Savitsky EA.  Wolff-Parkinson-White Syndrome. Emedicine. Apr 27, 2010. Accessed at:   http://emedicine.medscape.com/article/761066-treatment
3. Terry P, Lumsden G.  Intravenous Adenosine can be used in Asthmatics.  Best Bets. March 2000 Accessed at:  http://www.bestbets.org/bets/bet.php?id=112
4. Marill KA, Wolfram S, deSouza IS, Nishijima DK, Darren K, Setnik G, Stair TO, Ellinor PT.  Adenosine for Wide-Complex Tachycardia:  Efficacy and Safty.  Critical Care Medicine Sept 2009 37(9):2512-2518. Abstract accessed at:  http://www.ncbi.nlm.nih.gov/pubmed/19623049