This 77 year old woman presents with a 2 hour history of recurrent episodes of feeling dizzy and "not quite right". She had a permanent pacemaker inserted 3 months ago, but this was removed because of persistent and severe pain at the insertion site of the pacemaker battery.
Figure 1: (R-0031R). This is the 12 lead ECG of R-0031 taken at 2104 hours
+ Describe the main findings in this ECG
- Sinus rhythm is present with a ventricular rate of about 79 beats per minute.
- The QRS complexes have a normal morphology, but the complexes in the frontal leads have a low amplitude
- The PR interval is prolonged.
Figure 2 is the rhythm strip of R0031 taken at 0054 during an episode of dizziness. Vertical markers (numbered 1 to 10) are inscribed at an interval that corresponds to 15 large squares. The time interval between two consecutive markers is thus 3 seconds (15 x 0.04 seconds).
+ Describe the main findings in this rhythm strip
- P waves are not seen
- The width of the QRS complexes is about 0.10 seconds, which is normal and indicates that the impulses arise above the ventricles (from the atria, AV node or bundle of His)
- The QRS complexes have two (slightly) different morphologies. All the complexes in the second strip and nearly all the complexes (except for the second complex) in the third strip have a Rs shape. Many of the complexes in the first strip and the fourth strip have a deeper S wave, at times producing a RS shape. The normal width of these complexes indicates that they arise above the ventricle. Since the main problem is failure of impulse formation we will not distinguish between the Rs and RS complexes in our analysis.
There are three ventricular rhythm "patterns"
- An irregular rhythm is present between markers 1 and 3, with a ventricular rate of about 80 beats per minute in the interval between markers 1 and 2. This represents atrial fibrillation with a slow ventricular response
- During the 18 second interval between vertical markers 3 and 9 the ventricular rate is about 33 beats per minute (with a range from 20 beats per minute to 60 beats per minute). The interval between the ventricular beats is irregular. Ventricular escape beats are not seen. This part of the rhythm strip sows sinus pause (sinus arrest)
- A regular narrow complex tachycardia (with a ventricular rate of about 150 beats per minute) develops in the bottom strip, beginning just before marker 10. This is a supraventricular tachycardia
The rhythms in Figure 2 alternate with longer periods of sinus rhythm. The sequence of rhythms seen in this case are: sinus rhythm → atrial fibrillation (with a slow ventricular response) → sinus pause (with a very slow junctional escape rhythm) → supraventricular tachycardia → sinus rhythm.
These findings are consistent with sick sinus syndrome (bradycardia-tachycardia syndrome).
+ What drug(s) could be used to treat the rhythm(s) in Figure 2 ?
Atropine was given intravenously, but did not have any effect on the rhythms.
An intravenous isoprenaline infusion was commenced at a dose of 0.1 microgram/minute, aiming to titrate the dose in 0.1 microgram/minute increments to a maximal dose of 0.5 microgram/minute.
An isoprenaline dose of 0.2 microgram/minute increased the heart rate during periods of sinus pause without markedly increasing the ventricular rate during the periods of supraventricular tachycardia