Torsades de Pointes (TdP) on the ECG for nurses & nursing students
All Torsades de Pointes are polymorphic VT but not all polymorphic VT is Torsades.
What does this mean? Torsades de pointes (a twisting of the points; TdP) describes a very specific form of polymorphic VT. The “twisting of the points” to which the name refers describes multiple ventricular ectopic sites rotating around the heart, changing its electrical “axis” as they do so. This occurs at very rapid rates, up to and around 250 beats per minute!
Remember, the axis describes the vector of the heart (the direction the depolarization waveform travels). If the area of the ventricles initiating the depolarization is constantly rotating and shifting, then you would expect the morphology of the QRS to change along with this! As the electrical foci rotate and spiral around the heart a beautiful but dangerous “bowtie appearance” ventricular tachycardia presents on the rhythm strip.
Why should we care? Hallmark causes of TdP are low magnesium/potassium levels and a prolonged QT interval, although profound bradycardias, heart attack or coronary perfusion defects may precipitate this. Remember that the QT interval represents complete ventricular depolarization and repolarization. If the QT interval is prolonged, then the T wave extends further from the QRS complex. The heart is electrically sensitive and refractory to depolarizing during this phase (T wave) and if a premature ventricular contraction occurs, its R wave just might land on the T wave. When this happens, the heart is sent into this electrically chaotic rhythm resulting from this “R on T” phenomenon.
Causes of long QT syndrome may also include genetic predisposition or electrolyte imbalances. Interestingly, some antiarrhythmic medications that function to prolong this cycle may predispose patients to this. For this reason, medication loading protocols exist in which serial ECGs are taken to monitor the QT interval. As with other forms of VT, patient presentation will guide therapy and determine if medications or electrical therapies (defibrillation) will be used.
Torsades de Pointes (TdP) recognition key points:
A distinct type of polymorphic VT in setting of prolonged QT interval.
From French meaning “twisting of the points” describing the spiraling change in direction (axis) and amplitude of QRS.
On the ECG, look for:
Classic bowtie or party streamer appearance (images below) = hallmark depiction.
Usually initiated by PVC landing on T wave (R on T phenomenon).
Underlying QT prolongation evidence.
Polymorphic ventricular tachycardia (PVT) without QT prolongation may be due to many causes (ischemia, drug toxicity, and more).
QT prolongation may be acquired or hereditary Acquired may include antiarrhythmic and other drug therapies, electrolytes disturbances (especially K, Mg), severe bradyarrhythmias, and more. Hereditary causes may include abnormal ion channel function in the heart. A combination of factors above may be present and contribute to this.
Hope this helps!
*From a single lead basic rhythms and nursing perspective. Exceptions and additions may exist.
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Giudicessi, J. R., Tester, D. J., & Ackerman, M., J. (2022). Genetics of cardiac arrhythmias. In P. Libey, R. O. Bonow, D. L. Mann, G. G. Tomaselli, D. L. Bhatt, S. D. Solomon, & E. Braunwald (Eds.) Heart disease: A textbook of cardiovascular medicine (pp. 1191-1207). Elsevier.
Stevenson, W. G., & Zeppenfeld, K. (2022). Ventricular arrhythmias. In P. Libey, R. O. Bonow, D. L. Mann, G. G. Tomaselli, D. L. Bhatt, S. D. Solomon, & E. Braunwald (Eds.) Heart disease: A textbook of cardiovascular medicine (pp. 1288-1311). Elsevier.
