Torsades de Pointes​

Torsades de Pointes = a form of polymorphic VT that is caused by the R-on-T phenomenon in the setting of prolonged QT​

• Produces a characteristic morphology of waxing and waning QRS complexes​
  • Hence the names "Twisting of the points"

R-on-T Phenomenon​

The QT interval represents the onset of ventricular depolarization to the end of repolarization​

• This includes the relative refractory period, wherein the threshold for impulse conduction is lowered ​
• If QT is  increased, so is this relative refractory period​
• A stimulus provided at this point (R-wave) can induce dangerous ventricular arrhythmias such as VT, VF and Torsades De Pointes

Causes of R-on-T​

What can cause this phenomenon?​

1) QT prolongation (most commonly!)​

• May occur due to:​
  • Inherited conditions​
  • Medication toxicity/overdose​
  • Electrolyte imbalances and other metabolic causes​

2) Ectopic electrical impulse​

• Non-synchronized cardioversion​
• Blunt trauma to the chest (commotio cordis)

Sound Familiar?​

We discussed Long QT in the setting of the introduction of Ondansetron for ALS-PCS v5.0/5.1​

• Ondansetron is a medication that can prolong the QT ​
  • In general, a single dose administered by paramedics will not be an issue​
  • BUT, can trigger R-on-T phenomenon in those with known QT syndrome​
    • This is why Ondansetron is contraindicated in patients with known "Prolonged Long QT Syndrome"

Treatment of Torsades de Pointes​

• Basics of arrythmia management: C, A, B​
  •  Check for a pulse – may not have one in sustained Torsades​
    • If no pulse: Treat per the Cardiac Medical Arrest Medical Directive​
    • If pulse present: Supportive management and prepare for arrest​
      • ACPs: Can consider synchronized cardioversion​​
  •  Support A and B throughout​
• In-hospital the cause of the Torsades will be sought, and treated, along with the supportive care

Summary​

• Torsades de Pointes is a special form of polymorphic V-Tach, caused by the R-on-T phenomenon​
• There is inherent safety written into the Nausea/Vomiting Medical Directive to reduce the risk of causing this condition with Ondansetron administration​
• Paramedics should be able to recognize and treat this arrhythmia using basic resuscitation principles

No additional resources available for this #SWORBHPTip.