Stem: Twenty nine year old man with a past history of intermittent palpitations. He is not taking any medications. He presents with palpitations, dyspnoea and dizziness that came on while he exercising in the gym. His systolic blood pressure on arrival was 60 mm Hg.
Rhythm strips taken between 2147 and 2237 are shown in Figure 1.
+ List the significant findings in the ECG rhythm strip and provide the most likely or important diagnosis.
- The rhythm is irregular, and the average ventricular rate is about 240 beats per minute (with a range of 125 to 375 beats per minute)
- The QRS complexes are widened and have a abnormal and variable shape: the first 8 complexes differ markedly in their shape, the 10th complex and the 11th to 15th complexes have the same shape (with a [regular] R-R interval of about 320 msec), and the shape of following complexes is again very variable
- There is no identifiable atrial activity
- The QRS morphology and the rapid [average] ventricular rate suggest polymorphic ventricular tachycardia, but the marked irregularity raise the possibility of atrial fibrillation in pre-excitation syndrome
- The two strips are continuous, but there is a pause in recording in the upper strip, seen as a straight line between the left two-thirds and the right third of the strip
- Upper strip: The wide QRS complex tachycardia continues. The complexes in the left third of the strip and the right third of the strip have a similar morphology: QS wave followed by a tall T wave. The R-R interval between theses complexes is constant at 200 msec (corresponding to a ventricular rate of 300 beats per minute). There are small notches on the downstroke and upstroke of these QS waves that could represent atrial activity - their pattern does not correspond to atrioventricular dissociation. In the middle third of the strip the complexes have a different (RS) morphology and the R-R intervals are longer and slightly irregular
- Lower strip: A wide complex irregular tachycardia with variable QRS morphology is the main finding, but the 5th (wide) QRS complex is followed by a pause and the appearance of two narrow QRS complexes (6th and 8th complex) that have a small delta wave. This confirms the diagnosis of atrial fibrillation in pre-excitation syndrome
- There is a regular rhythm with a ventricular rate of about 300 beats per minute. The QRS complexes are wide and have the same morphology. Electrical alternans is present. Atrial activity is not visible. If this was the initial rhythm strip the differential diagnosis would be between monomorphic ventricular tachycardia and atrial flutter with 1:1 conduction. Given the preceding rhythm strips in this case, the likely diagnosis is pre-excitation syndrome with atrial flutter and and 1:1 antidromic [atrioventricular re-entrant] tachycardia
- Sinus tachycardia at a rate of about 107 beats per minute. The PR, QRS and QT intervals are normal. A delta wave is not seen
A 12 lead ECG after reversion to sinus rhythm is shown in Figure 2, confirming the diagnosis of pre-excitation syndrome
The initial treatment options in a patients with pre-excitation and atrial fibrillation are intravenous flecainide (if not contraindicated) followed by electrical cardioversion.
- These patients need early review by a cardiac electrophysiolgist for risk stratification and a decision about ablation.