Case Study: SVT Management

Case study time! This is the ekg of a patient that came in reporting palpitations and chest discomfort, HR was 220, and patient was becoming hypotensive 80/50

A. What is this heart rhythm called?
B. What vital sign is most important to check in this patient and must be done manually?
C. How is this heart rhythm typically treated?
D. How would you treat this unstable symptomatic patient?

Answers

A. What is this heart rhythm called?

• This rhythm classifies as supraventricular tachycardia or SVT, SVT is an abnormally fast heart rate >150 and originates above the ventricles.

B. What vital sign is most important to check in this patient and must be done manually

• One of most important things to check with these patients, if they are unconscious, is going to be pulse!  Without a pulse this rhythm would be classified as pulseless electrical activity and CPR must be started immediately!  This vital sign is followed by a blood pressure so you can determine if the patient is hemodynamically stable.

C. How is this heart rhythm typically treated?

• Management of this patient consists of identifying and treating the underlying cause.  Maintaining airway, applying oxygen, cardiac monitor, obtaining all vitals, EKG, IV access.  
  • Vagal maneuvers are often the first line of treatment , however there is debate on the appropriateness and effectiveness of these maneuvers in SVT management.  Examples of vagal maneuvers consist of coughing, bearing down, cold stimulus to the face, carotid massage (only one side should be massaged at a time, and should not be done on patients with carotid artery stenosis), or gagging.
    • Science behind it: Vagal maneuvers stimulate aortic baroreceptors, these receptors trigger an increase in vagal tone which stimulates a bradycardia response, prolongs refractoriness of the nodal tissue and disrupts the re-entry circuit.
  • Adenosine is often tried second if the vagal maneuvers fail on a stable patient.  The first dose consists of 6 mg of adenosine administered rapidly over 1-3 seconds, followed by a flush, if the patient is not converted after 1-2 minutes, a second dose of 12 mg may be given.  Adenosine must be given as fast as possible due to its short half life, this is best achieved using a 3-way stop cock. Also ensure everything is needed at bedside for resuscitation prior to administration.
    • Science behind it:  Adenosine binds to purinergic receptors causing vascular smooth muscle relaxation, resulting in vasodilation, adenosine also inhibits calcium entry decreasing conduction velocity in the AV node and inhibits pacemaker cells, decreasing their firing rate.
  • Synchronized cardioversion is often recommended for unstable SVT patients who are hemodynacially unstable and individuals that were not converted with vagal maneuvers or adenosine.  initial doses depend on the rate (narrow regular 50-100 J, narrow irregular biphasic 120-200 J, narrow irregular monophasic 200 J, wide regular 100 J, wide irregular defibrillation dose).  Also ensure everything is needed at bedside for resuscitation prior to administration.
• Science behind it: Synchronized cardioversion is used to restore sinus rhythm in patients.  It does this by providing a timed shock at a specific point in the QRS complex, depolarizing all or a majority of excitable myocardium to terminate reentry pathways.  It is important that your shock is synced prior to administration because if it was given during the T wave it may induce ventricular fibrillation.
  D. How would you treat this unstable symptomatic patient?

D. The key to answering how to treat this specific patient is looking at if they are stable or unstable.  With the heart rate in the 220’s and a blood pressure of 80/50 she falls into the unstable category as she is hemodynically unstable!  This calls for immediate cardioversion at 50-100 J.

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