What is the key point for torsades de pointes on an electrocardiogram (EKG)?

Key Diagnostic Features of Torsades de Pointes on ECG

The most critical ECG feature of torsades de pointes (TdP) is the characteristic short-long-short R-R cycle sequence that initiates the arrhythmia, typically with a premature ventricular complex (PVC) followed by a compensatory pause and then another PVC. 1

ECG Characteristics of Torsades de Pointes

Essential Diagnostic Features

• QTc interval prolongation >500 ms (considered dangerous for both males and females) 1
• Polymorphic ventricular tachycardia with twisting QRS complexes around the baseline 2
• Short-long-short initiating sequence pattern 1, 3
• PVC that falls near the peak of a distorted T-U complex 1

Additional ECG Signs of Impending TdP

• T-U wave distortion that becomes exaggerated after a pause 1
• Visible (macroscopic) T-wave alternans 1
• New-onset ventricular ectopy and couplets 1
• QTc increase of ≥60 ms from baseline 1, 4
• "Warm-up" phenomenon with initial R-R cycles longer than subsequent cycles 1
• Abrupt switching of QRS morphology from predominantly positive to predominantly negative complexes 1

Risk Factors for TdP

Patient-Specific Risk Factors

• Female sex 1, 4
• Advanced age 1, 4
• Heart disease (especially congestive heart failure, myocardial infarction) 1
• Bradycardia or rhythms with long pauses 1
• Genetic predisposition 1

Modifiable Risk Factors

• QT-prolonging medications 1, 4
• Concurrent use of multiple QT-prolonging drugs 1, 4
• Electrolyte abnormalities:
  • Hypokalemia 1, 3
  • Hypomagnesemia 1, 3
  • Hypocalcemia 1, 4
• Treatment with diuretics 1
• Impaired hepatic drug metabolism 1
• Rapid IV infusion of QT-prolonging drugs 1

Management Algorithm for TdP

Immediate Actions

1. Discontinue any offending QT-prolonging drugs 1, 5
2. Administer IV magnesium sulfate 1-2g over 5-15 minutes (first-line therapy regardless of serum magnesium level) 1, 6, 7
3. Correct electrolyte abnormalities (maintain potassium in high normal range) 1, 5
4. For hemodynamically unstable TdP: immediate defibrillation 1, 6

For Recurrent TdP

1. Increase heart rate to shorten QT interval:
   • Temporary transvenous pacing 1, 6, 3
   • IV isoproterenol (isoprenaline) titrated to heart rate >90 beats per minute 1, 6, 7
2. Transfer patient to highest level of ECG monitoring with immediate defibrillation capability 1

Monitoring Recommendations

• Continuous ECG monitoring until QT prolongation resolves 6
• Regular assessment of electrolytes, especially potassium and magnesium 1
• For patients on QT-prolonging medications: baseline ECG, follow-up ECG 7-15 days after initiation or dose changes, and periodic monitoring 1

Pitfalls to Avoid

• Administering additional QT-prolonging antiarrhythmic drugs (can worsen TdP) 7
• Failure to recognize early warning signs of impending TdP (T-wave alternans, new PVCs) 1
• Overlooking drug interactions that increase QT-prolonging drug concentrations 4
• Inadequate dose adjustment of renally eliminated QT-prolonging drugs in kidney disease 4

Remember that TdP can rapidly degenerate into ventricular fibrillation and sudden death if not promptly recognized and treated 5. The characteristic short-long-short initiating sequence is the most distinctive feature for diagnosis on ECG 1, 3.