Airway & Respiratory, Cardiac & Resuscitation, Patient Care

Pothole’ Conversion: External mechanical force reverses supraventricular tachycardia

Issue 6 and Volume 34.

Supraventricular tachycardias (SVTs) are tachydysrhythmias originating above the ventricles, in the atria or atrioventricular (AV) nodal tissue. Management of these dysrhythmias includes vagal maneuvers (i.e., Valsalva, ice packs to the face and/or carotid massage), pharmacologic therapy and electrical cardioversion.„

The use of such external mechanical forces as a “precordial thump” has been used to convert these dysrhythmias to a normal rhythm. This report presents the case of a patient with an SVT that was converted by external mechanical forces provided by a bump in the road during emergency transport to the hospital.„

Case Report
An ALS ambulance responded to a minor traffic collision, and the crew evaluated a 21-year-old male who was restrained in the front seat. There was only minor damage to the vehicle, and the patient was not entrapped. He was found to have no injuries from the collision; however, he did complain of a racing heartbeat. His initial vital signs were: heart rate 193, BP 111/56, respiratory rate 16, and oxygen saturation of 100%.„

The patient denied any chest pain, difficulty breathing or light-headedness. He did note a history of intermittent “fast heart rate,” especially with exertion. He denied use of any medications, illegal drugs or excessive caffeine intake and had no known allergies.„

The patient was placed on a cardiac monitor revealing SVT (see Figure 1). He remained hemodynamically stable during transport. Multiple vagal maneuvers (Valsalva and carotid massage) were attempted, but were unsuccessful at converting the rhythm. While en route, the ambulance hit a significant bump in the road, and a decrease in the patient_s heart rate was noted. Immediately following the bump, the rhythm strip demonstrated a sinus rhythm with a rate of 96 (see Figure 2).„

The patient was evaluated in the emergency department and found to have no injuries or complaints, and he remained in normal sinus rhythm. He was discharged with cardiology follow-up and underwent radio-frequency ablation treatment for a left heart re-entry pathway without complication.

SVT includes a wide variety of dysrhythmias. A few origins include atrial fibrillation with rapid ventricular response, atrial flutter with rapid conduction and intra-atrial re-entrant tachycardia. SVT can also be the result of AV nodal activation with a rapid rate (junctional tachycardia) and such re-entry tachycardias as Wolf-Parkinson-White or Lown-Ganong-Levine (LGL) syndromes. LGL is a re-entry tachycardia with a short P-R interval but without a Delta wave on ECGs.

Current treatment for tachycardia with a pulse is dependent on the patient_s symptoms and stability. If the patient is unstable (chest pain, abnormal vitals, altered mental status), then immediate synchronized cardioversion is the treatment of choice. If the patient is stable, then treatment options are based on two criteria: QRS complex width and regularity of rhythm.„

This patient had a narrow, complex, regular tachycardia consistent with SVT. The conversion seems to be attributable to an external mechanical event caused by the bump in the road, similar to a precordial thump. Although unusual, this has been reported at least once in the medical literature.

The American Heart Association (AHA) no longer recommends the use of a precordial thump in its Advanced Cardiac Life Support (ACLS) guidelines for cardiac arrest. A recent study demonstrated the ineffectiveness of the precordial thump in converting malignant ventricular arrhythmias. The amount of energy delivered by a precordial thump has not been determined. The energy delivered would have to be enough to result in cardioversion of SVT, and at least 50 joules, based on current ACLS guidelines.

It was demonstrated that the precordial thump, under normal oxygenation, opened nonselective stretch-activated channels, which repolarize the cell. It_s been suggested that in„commotio cordisƒsudden death caused by blunt chest traumaƒventricular fibrillation (V-fib) is induced by a light blow delivered over a wide range of velocities. A case report demonstrated this in a 57-year-old male who developed V-fib after a precordial thump.

This case, however, demonstrates that external mechanical forces can convert an SVT rhythm. Only one other reported case of so-called “pothole” conversion of a patient with SVT was located in the literature.„

An external mechanical force may convert an SVT as presented here. However, delivering sufficient energy may require a large mechanical force with appropriate timing of the delivery of the blow to prevent worsening of the dysrhythmia.

Due to the risks associated withcommotio cordis, unknown efficacy and unknown amount of energy delivery, we should continue to follow the AHA guidelines of vagal maneuvers, pharmacologic therapy or electrical cardioversion as the primary methods of converting SVT. External mechanical forces should be avoided due to the risks mentioned above. Because potholes and other road hazards may be impossible to avoid and can be struck without warning, EMS providers should always reassess their patient_s cardiac rhythm whenever a jarring force is transmitted to the patient during transport.JEMS

  1. American Heart Association: “2005 ACLS Guidelines ACLS Tachycardia Algorithm.” Circulation. 112:IV-67-IV-77, 2005.
  2. Wong MP, Armstrong PW: “Supraventricular tachycardia terminated by external mechanical stimulation: A case of Âpothole conversion._” Pacing and Clinical Electrophysiology. 22(2):376Ï378, 1999.
  3. American Heart Association: “2005 ACLS Guidelines Management of Cardiac Arrest.” Circulation. 112:IV-58-IV-66, 2005.
  4. Amir O, Schliamser JE, Nemer S, et al: “Ineffectiveness of precordial thump for cardioversion of malignant ventricular tachyarrhythmias.” Pacing & Clinical Electrophysiology. 30(2):153Ï156, 2007.
  5. Li W, Kohl P, Trayanova N: “Myocardial ischemia lowers precordial thump efficacy: An inquiry into mechanisms using three-dimensional simulations.” Heart Rhythm. 3(2):179Ï186, 2006.
  6. Link MS, Maron BJ, Wang PJ, et al: “Upper and lower limits of vulnerability to sudden arrhythmic death with chest-wall impact (commotio cordis).” Journal of the American College of Cardiology. 41(1):99Ï104, 2003.
  7. Cayla G, Macia JC, Pasquie JL: “Precordial thump in the catheterization laboratory experimental evidence for commotio cordis.” Circulation. 115(11):e332, 2007.„„„

Steven Bauer,MD, is a major in the U.S. Army at Carl R. Darnall Army Medical Center Department of Emergency Medicine. He has been practicing emergency medicine for five years. He served for two and a half„years as brigade surgeon for 2nd Brigade 4th Infantry Division. He_s the former medical director for EMS at Fort Hood, Texas. He will take on the role of clinical assistant professor of emergency medicine at West Virginia University Hospitals-East in July 2009. Contact him at[email protected] or[email protected]

For more on electrical conversion, read “Heart Rate 310” from March 2008 JEMS