A Case of Sick Sinus

This 50 year old woman presented with palpitations. There is a past history of hypertension and non insulin dependent diabetes. There was no chest pain, and her vital signs were normal.

The initial ECG at 1810

The initial ECG at 1810

Rhythm strip recorded soon after arrival.

Rhythm strip recorded soon after arrival.

ECG at 1925 after the patient had been treated with intravenous verapamil

ECG at 1925 after the patient had been treated with intravenous verapamil

We will begin with the rhythm strip.

This shows intervals of atrial fibrillation,  with a ventricular rate of about 180 beats per minute in the top strip. There are also three pauses (P1 to P3), with a single sinus beat in the second pause (P2).  Some of the QRS complexes are preceded by an upward deflection that is suggestive of a delta wave (see the QRS complexes in the middle strip). This upward slope appearance is most marked when the ventricular rate increases to 200 beats per minute or more, as seen in the first half of the middle strip (the R-R intervals of some of the complexes in this strip are also shown). The upward slope is most likely due to aberrant ventricular conduction or merging of the ST-T segments with the QRS complexes. An accessory pathway is unlikely.

This shows intervals of atrial fibrillation,  with a ventricular rate of about 180 beats per minute in the top strip. There are also three pauses (P1 to P3), with a single sinus beat in the second pause (P2).  Some of the QRS complexes are preceded by an upward deflection that is suggestive of a delta wave (see the QRS complexes in the middle strip). This upward slope appearance is most marked when the ventricular rate increases to 200 beats per minute or more, as seen in the first half of the middle strip (the R-R intervals of some of the complexes in this strip are also shown). The upward slope is most likely due to aberrant ventricular conduction or merging of the ST-T segments with the QRS complexes. An accessory pathway is unlikely.

Next we look at the precordial leads of the initial tracing taken at 1810.

The initial QRS complexin V1 to V3 has normal morphology, but the next three complexes have a right bundle branch block pattern that is consistent with   rate related aberrant conduction.

The initial QRS complexin V1 to V3 has normal morphology, but the next three complexes have a right bundle branch block pattern that is consistent with   rate related aberrant conduction.

The ECG taken at 1810 shows tachycardia-bradycardia syndrome (sick sinus syndrome), with a dominant rhythm of atrial fibrillation with a ventricular rate of 180 - 200 beats per minute. There is an intermittent, rate related,  right bundle branch block.

The initial management of this case would be to slow the fast ventricular rate with a drug that will slow conduction through the atrioventricular node (AVN).  We could start with intravenous magnesium, followed by digoxin or amiodarone (starting at low initial doses). I would avoid intravenous administration of more than one AVN blocking drug.

The second ECG at 1925 shows atrial fibrillation with a ventricular rate of about 100 beats per minute.