Torsades

Thanks to Mathew Adamson for this interesting case that he managed on 16th September 2015.

The patient is a 91 year old man with a past history of atrial fibrillation, permanent pacemaker,  and a left internal iliac artery aneurysm that had been coiled.  His medications included citalopram, digoxin, atorvastatin, frusemide, atenolol, rabeprazole, allopurinol and nizatidine. He was not on any anticoagulants at present;  warfarin administration four weeks previously had been associated with macroscopic haematuria needing transfusion of three units of blood.  A CT angiogram at that time showed a fistula between the left internal iliac artery and the bladder. 

Prior to the patient's arrival the Emergency Department was told that the patient had developed macroscopic haematuria, and had had a syncopal episode associated with trauma to the head. 

On arrival he had a GCS of 15 and a systolic blood pressure of 100 mm Hg.  There was no chest pain

+ Describe the major findings on ECG0011A which was taken on arrival at 2037.

The enlarged rhythm strip (see the above figure)   shows narrow QRS complexes (QRS duration of 92 msec on the computer report) with irregular R-R intervals and no visible P waves.  The patient thus has atrial fibrillation.   A horizontal line that is 15 large squares long marks an interval of 3 seconds. There are five QRS complexes in this 3 second interval, so the ventricular rate is 100 beats per minute.   There is slight (horizontal) ST segment depression in Leads II, III, aVF and V2 - V6. 

There is marked (symmetrical)  T wave inversion in  Leads II, III, aVF and less marked T wave inversion in Leads V4 - V6.  The T wave is upright is Lead aVR. These changes were present in an ECG recorded 3 months ago.

The computer reports a prolonged QTc interval of 520 sec (the upper limit of normal of the QTc in males is 470 msec and in females is 470 msec). We can confirm that the QTc is prolonged by:

  • Observing that the QT interval is longer than half the preceding R-R interval in the rhythm strip.
  • Doing our own calculation using one of the various published formulas.

These formulas often correct for the changes in the QT interval that occur with changes in the heart rate.  We will use Bazett's formula:   QTc = QT / √(RR)  where RR is derived from the measured heart rate (HR) using the formula: RR = 60 ÷ HR i.e. 60∕ HR.

Using the above rhythm strip:

QT = 10 x small squares (each is 40 msec) = 400 msec  

RR =  60∕100 = 0.60

√RR = √0.6 =  0.775

QTc = 400∕0.775 =  516 msec

The QT interval is the time taken for depolarization and repolarization.  An increase in the QT interval or QTc interval is due to lengthening of repolarization.  Changes in repolarization also alter the ST segment or the T wave. These changes are usually described qualitatively,  but the T wave changes also can be described by measuring the T wave axis in the frontal leads.  We will use this case to measure the frontal T wave axis, and compare it to the QRS axis. 

We start by arranging the frontal lead complexes in the Cabrera format.  This format helps us establish the direction of vectors (both depolarization and repolarization)  from the shape of the QRS complex in the different leads.  The most commonly measured vector is the  vector of ventricular depolarization;  the direction of this vector is the "axis" of the heart.

In the above figure the QRS  vector is indicated by the purple arrow labelled QRS.  The QRS vector (or axis) is thus located at  about + 50 degrees (the computer locates this QRS vector is + 38 degrees).   This frontal plane QRS axis is in the normal range.

The direction of other vectors (e.g those that produce the P wave,  the ST segment or the T wave)  can also be   determined. The T waves in the inferior leads are inverted,  the T wave in Lead I is not visible and the T waves in Lead aVR and Lead aVL are upright.  The direction of the T wave vector is thus - 90 degrees, indicated by the red arrow labelled T. 

In a normal ECG the T waves are upright in Leads 1, II and aVF.  The T wave in Lead III can be upright.  flat or inverted.  This means that the normal range of the T wave vector is between 0 degrees and + 60 degrees.

Summary of the main findings in ECG0011A:

  • Atrial fibrillation with a ventricular rate of about 100 beats per minute
  • Slight ST depression and marked symmetrical T wave inversion most marked in the infero-lateral leads
  • Normal QRS axis (and abnormal T wave axis)
  • Prolonged QTc interval
 

The patient's vital signs remained stable, and there was no further haematuria.    A CAT angiogram was carried out without any problems. After the patient returned from the CAT scan there was a change in the rhythm seen on his monitor.  You are asked to review this tracing (ECG_0011_B) taken at 2126.

+ Describe the major findings on ECG_0011_B and the underlying rhythm(s).

The rhythm strip in ECG_0011_B shows five single beats with normal QRS morphology followed by episodes of non-sustained polymorphic ventricular tachycardia. The initial QRS complexes in the first to fourth episodes of polymorphic tachycardia have the same shape.


Enlarged view of the rhythm strip of ECG_0011_B

Each episode of polymorphic tachycardia begins with a ventricular ectopic beat that arises near the mid-point of the inverted T wave of the preceding QRS complex. These are “R on T” ectopics, and have a short coupling interval (the horizontal blue arrows show a coupling interval between 240 msec and 320 msec).

Polymorphic ventricular tachycardia in a person with a prolonged QTc interval is called torsades de pointes. The same term is also used to describe ventricular tachycardia with a characteristic morphology that can occur in patients with a normal QT interval.

The term torsade de pointes was coined by the French physician Dessertennes in 1966. It means ‘twist of spikes’ (torsade – a decorative twist of braid, ribbon or artificial plait of hair).

The patient was treated with blood transfusion and intravenous administration of potassium and magnesium. The torsades de pointes resolved.