A 40-year-old man presented to the emergency department with two hours of rapid regular palpitations and dizziness. He denied vertigo, chest pain, shortness of breath, and syncope, and he said he had never had palpitations like this. His symptoms started suddenly and are continuous. He denied any significant prior medical history and tobacco, alcohol, and drug use, and he takes no prescription medications.
His vital signs were normal except for a softish blood pressure of 101/84 mm Hg and a pulse rate of 196 bpm. His head and neck exam was normal with no thyromegaly or jugular vein distention. His lungs were clear, and his heart was regular but tachycardic. The abdomen was benign, and the legs had no chords, tenderness, or edema.
The precordial leads of an ECG:
- What is the rhythm?
- What is initial treatment of choice?
- What is the second-line treatment?
- What medication is overused for this condition?
The patient's rhythm is supraventricular tachycardia (SVT), and the initial treatment should be a modified Valsalva maneuver. The second-line treatment is diltiazem. Adenosine is overused for this condition.
SVT: Rate 125-250 and regular. If the rate is under 200, consider Wolff-Parkinson-White syndrome.
Causes: Usually idiopathic, but consider these causes with the acronym TWAM: TCA, WPW, Autism spectrum disorder, MI/mitral valve prolapse.
Tests: K, MG, post-conversion ECG, troponin only needed if clinical concern for ischemia.
Treatment: Modified Valsalva first, then diltiazem. Both are better than adenosine.
Treatment Rate Method/Dosing
Modified Valsalva ~40% Hold for 15 sec., then supine with
45° leg raise for 15 sec.
Regular Valsalva ~15% Not recommended, but if used, hold
for > 15 sec.
Diltiazem IVPB* ~98% 10-20 mg. Cheaper, safer, and easier to
use than adenosine,
Adenosine IVP* ~87% Not recommended, but if used, start
with 6 mg; repeat 12 mg.**
* If rate >200, consider WPW and avoid all AV nodal blockers.
** 3 mg dose if on Tegretol, Persantine, or Aggrenox. Avoid if WPW or heart transplant.
Prevention: Replete K and Mg; metoprolol, diltiazem, or verapamil; ablation
SVT is a regular tachycardia that usually has a paroxysmal onset and a regular rate between 125 and 250 with no P waves and a narrow QRS. Symptoms are primarily palpitations and lightheadedness. Chest pain, dyspnea on exertion, and syncope or near-syncope may also occur. Most cases are idiopathic, but SVT can be triggered by a variety of cardiac conditions as well as certain antidepressants. Low potassium and magnesium may also contribute.
Treatment of SVT has been primarily with adenosine in the recent past. A Valsalva maneuver may be tried first, but success rates are only about 15 percent. Recent studies have shown there is a better medication and a better Valsalva maneuver. The modified Valsalva, which consists of a Valsalva for at least 15 seconds followed by a passive leg raise, has been shown to terminate SVT in about 40 percent of patients. Diltiazem, with an initial dose of 15 mg, has been shown to be about 10 percent more effective than adenosine, with the additional benefits of a better safety profile, decreased cost, and patient preference.
Patients diagnosed with SVT can usually be discharged home with cardiology follow-up. Prevention for frequent or severe episodes may include beta or calcium channel blockers and ablation by an electrophysiologist.