Tell-Tale Heartbeat: Pharmaceutical and Alternative Management of Supraventricular Tachycardia

Tell-Tale Heartbeat: Pharmaceutical and Alternative Management of Supraventricular Tachycardia

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The page from the NICU came early in my shift. I waited for a moment and breathed a sigh of relief that there was no second overhead page to the code team. I was working as an EKG tech at a large community hospital, and when I came in to start my shift a stack of EKGs from the neonatal unit was on the cart — the nurses had clearly been trying to capture something during the night shift. I raced through the halls and tapped my feet impatiently under the sink as I went through the mandatory four-minute scrub protocol required before entering the NICU.

As I washed, a nurse explained to me that they had a preemie who was having runs of SVT (supraventricular tachycardia, where the upper chambers of the heart were beating too quickly), and they needed a 12-lead, as well as a better rhythm strip for the pediatric cardiologist who was on his way over from the university hospital. I had just gotten my tiny patient hooked up to the EKG machine when the doctor appeared at my elbow. We obtained a clear EKG and ran a strip for a moment, but the baby’s heart rate was racing along well above 200 beats per minute, and we needed to get her back down to a normal sinus rhythm.

“Watch this,” said the cardiologist. He popped a pacifier in the baby’s mouth and then covered her nose with a plastic bag of ice chips. Like magic, a few seconds later, her heart rate slowed and she converted to a sinus rhythm. It was the diving reflex, he told me. It increased vagal tone and stopped the arrhythmia.

What If the Diving Reflex Had Failed?

Had the diving reflex not worked for our preemie, the doctor had a syringe of verapamil standing by, which is often given intravenously to convert acute cases of SVT. Because verapamil is a calcium channel blocker and is usually only given to pediatric patients at least one year old, the physician also had a syringe of calcium at the bedside.

Verapamil is usually administered as a 5-10 mg bolus (0.075-0.15 mg/kg) over 2 minutes, with a second dose given in 15-30 minutes if there is no conversion. Some institutions recommend infusing verapamil over 3 minutes in geriatric patients. The pediatric dose of verapamil is 0.1-0.3 mg/kg given as an IV bolus over 2 minutes, with a repeat dose 30 minutes later, if needed.

Be forewarned, there can be a long pause after giving verapamil before the patient converts to sinus rhythm. It’s usually only a few seconds, but it can seem like minutes, as you wait with bated breath for a positive result.

Verapamil can also be administered as an IV drip for continuous infusion, with the dose titrated to produce an acceptable ventricular rate. The standard dose is a loading dose of 10 mg, followed by 0.375 mg/min for 30 minutes, then 0.125 mg/min. Infusion rates should be calculated based on the solution. Verapamil IV is not Y-site compatible with sodium bicarbonate, ampicillin, oxacillin, or nafcillin. Continuous EKG and blood pressure monitoring must be maintained. Prolonged infusions may result in drug accumulation.

Intravenous verapamil is contraindicated in the following situations:

  • severe CHF
  • severe hypotension
  • 2nd or 3rd degree AV block
  • sick sinus syndrome
  • recent administration of an IV beta blocker

There are several IV drugs that are commonly used, in addition to verapamil, to treat acute episodes of SVT. Adenosine is one, especially for pediatric patients under three, but it has an extremely short half-life, causes uncomfortable flushing and chest fullness, and can sometimes produce rebound tachycardia. The beta blocker metoprolol is also sometimes used. Verapamil, however, has a longer half-life, which is thought to help maintain sinus rhythm longer after conversion. Verapamil IV can be purchased in pre-measured vials, but many hospitals with busy ERs, CCUs, and EP (electrophysiology) labs compound their own in D5W or NSS.

Advantages of Compounded Verapamil

The benefits of compounding verapamil, both IV and oral (see below) are many:

  • Some seniors and small children are unable to take pills. Verapamil can be compounded in a liquid suspension for easier administration. It retains its potency well, even up to 60 days after preparation.
  • Verapamil has a naturally bitter taste. Compounding can also add flavor to improve palatability.
  • Compounding can remove dyes that cause allergies. Recently, a manufacturer of oral verapamil discontinued production of a dye-free tablet, leaving only a blue dyed product available from their label. Many allergy-sensitive patients were able to continue receiving verapamil without dyes by obtaining their prescriptions from compounding pharmacies instead.
  • Sometimes a patient fares better with a dose below the minimum amount or in between two standard doses. Compounding allows for precise dosage adjustment and reduces the potential for error with pill splitting.
  • If physicians work regularly with a specific compounding pharmacy, they can be more confident about the quality of ingredients, efficacy, and drug preparation process than if they are subject to drugs being supplied by varying manufacturers through a commercial pharmacy. Likewise, hospital pharmacies have control over quality and sterility of parenterally administered products.
  • Institutions that use a high volume of IV verapamil can find it more economical to compound their own from raw ingredients.
  • Compounded verapamil can be put in an institution’s desired delivery system.
  • During drug shortages, compounding pharmacies are usually not affected.

Vagal Maneuvers to Treat SVT

Vagal maneuvers, like using the diving reflex, are the first line of treatment for stable SVT. (Unstable SVT is defined by the presence of ongoing chest pain or loss of consciousness and is treated by inpatient cardioversion.) They work by activating the parasympathetic nervous system which is conducted to the heart via the vagus nerve. The Valsalva maneuver is usually the first one suggested to patients. This entails holding the breath and bearing down, as if having a bowel movement. Carotid massage is generally only recommended for young patients, as it can precipitate stroke from an embolism.

Older pediatric patients and adults can also plunge the face in a bowl of ice water. I had a patient once who came in for an exercise tolerance test on the treadmill. He admitted to not feeling so well that week, which his family had written off to some past history of anxiety. However, he mentioned he had been swimming in his brother’s pool all week, as the weather was very hot. When he went swimming, he immediately felt better. Needless to say, his EKG revealed persistent SVT.

The bag of ice over the nose of my NICU patient accomplished the same effect as plunging in a cold pool. The pacifier was to prevent the infant, an obligate nasal breather, from resorting to mouth breathing.

Signs and Symptoms of SVT

Because the atria are not filling and emptying properly in SVT, the ventricles are not adequately supplied with blood to perfuse the body during systole. Decreased cardiac output results in symptoms such as

  • shortness of breath
  • dizziness
  • anxiety
  • pressure in the chest, jaws, neck, or arms
  • nausea
  • weak, fluttering heartbeat

On an EKG, supraventricular tachycardia will typically present with a heart rate of approximately 130-250 beats per minute, narrow QRS complexes, and P waves that are often indistinguishable from T waves or appear after the QRS complex (retrograde P waves).

Treatment of Paroxysmal, Persistent, and Chronic SVT in the Outpatient Setting

With the symptoms listed above, it’s no surprise that many patients experience discomfort when suffering bouts of SVT. Some have bursts of arrhythmia that come and go (paroxysmal), while others have steady EKG irregularities that can go on for weeks or more. Extreme persistent or chronic cases may be referred to the EP lab for radiofrequency ablation to permanently eliminate the arrhythmia.

Many patients are placed on oral therapy for long-term relief and improved cardiac output. There are several antiarrhythmics and beta blockers (digoxin, atenolol, etc.) given orally for long-term management of SVT. Verapamil, still often the drug of choice, is also dosed orally. The regular adult dose for SVT is 240-480 mg per day, divided into 3-4 doses. The pediatric dose should be determined by the physician based on the individual patient.

Pharmaceutica North America welcomes your questions about compounding verapamil for the treatment of of supraventricular tachycardia. Verapamil is a versatile drug and is also compounded for podiatric use. Stayed tuned for our next post in which we will discuss this alternative application, and contact Pharmaceutica North America to see how we can help meet your compounding pharmaceutical needs.

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