ECG of the Week: ECG of the Week - 10th June 2013

This ECG is from an 84 year old male.
Presents complaining of general lethargy, nausea, several episodes of diarrhea, and dizziness.
Past history of atrial fibrillation, diabetes, and hypertension.
Medications include aspirin, ACE inhibitor, statin, sulphonylurea, and digoxin.
He is conscious, vague but orientated, and his BP is 112 systolic.

Click to enlarge

Rate:

Rhythm:

Regular
Nil p waves visualised

Axis:

RAD (~160 deg)

Intervals:

PR - nil p waves
QRS - Prolonged (120-130ms)
QT - 550ms

Segments:

Wandering baseline makes assessment difficult

? Minor ST depression III, aVF, V5-6

Additional:

U waves

Best visualised lead II
Secondary to digoxin toxicity

Interpretation:

"Regularised AF"

Escape rhythm - likely junctional as QRS morphology similar post Tx
Atrial fibrillation
3rd Degree AV block

QRS Prolongation

likely secondary to hyperkalaemia

What happened ?

Our patient is on digoxin with clinical features that whilst non-specific are often associated with chronic digoxin toxicity. As the comments section suggests digoxin toxicity should rate high on our list of likely diagnosis with associated electrolyte abnormalities.

Urgent electrolytes and digoxin levels were performed and this patient had a digoxin level of 5.4 ng/ml and a potassium > 9.0 !

He was treated with digoxin immune Fab, following which a repeat ECG was performed.

Click to enlarge

The ECG following treatment shows rate controlled atrial fibrillation (~66bpm), normalisation of QRS width (80-100ms), and decreased prominence of the U waves.

Chronic Digoxin Toxicity

Digoxin toxicity seems to have featured heavily in the FOAM world this last month.
Two highlights are:

You can read more about the general management of digoxin toxicity in the following resources:

I like to just focus on ECGs with this blog but I thought we'd just touch on one of the unique features of chronic digoxin toxicity which is hyperkalaemia and "stone heart".

Hyperkalaemia, digoxin toxicity, and calcium therapy - 'Stone Heart'

Stone heart refers to life-threatening cardiac tetany due to the use of i.v. calcium to treat hyperkalaemia in the setting of digoxin toxicity.
The theory being:

Digoxin works by inhibiting cardiac sodium-potassium ATPase pump
This increases intracellular sodium and calcium in the cardiac myocyte
Increased intracellular calcium = increased contractility and automaticity
In toxic setting more calcium = cardiac tetany = irreversible contraction = death

First line treatment in chronic digoxin toxicity is Digoxin Immune Fab, a recommended empirical dose is 2 ampoules if features of toxicity, and 5 ampoules in the setting of cardiac arrest in which chronic digoxin toxicity is suspected. In the absence of Fab or as adjuncts to treat hyperkalaemia options include sodium bicarb, insulin / dextrose, and magnesium sulphate.

The Toxicology Handbook, which is a must own textbook for anyone doing Emergency Medicine and certainly the most useful EM book I own, states calcium is contraindicated in treating hyperkalaemia in the setting of digoxin toxicity. This is echoed by a number of other sources such as, this letter in the EMJ, and the eMedicine review of the emergency management of digoxin toxicity.

There is certainly an amount of debate as to the existence of the 'Stone Heart' and the danger of using calcium in the setting of digoxin related hyperkalaemia. I'm not going to go through this here as a number of other people have covered the topic more eloquently than I could, I will just link to some further readings below: