ECG Case 054

This is a tricky ECG!

There is evidence of atrial fibrillation, as evidenced by the irregular baseline with fibrillatory waves most prominent in V1-2.

NB. Fibrillatory waves are characteristically seen in V1-2 (which overlie the atria), as opposed to tremor artefact which may be in seen in multiple leads without a predominance for V1-2. 

However, the ventricular rhythm is regular. How can this be? AF is irregular by definition…

---

This is an example of “regularised AF” due to digoxin toxicity:

If this all seems like too much of a coincidence, then consider the pathophysiology of digoxin toxicity…

Mechanisms of Digoxin Toxicity

Digoxin toxicity produces a wide variety of dysrhythmias, due to:

• Increased automaticity of atrial, junctional and
  ventricular tissues — via actions at the Na/K and Na/Ca exchangers
  causing increased intracellular calcium and therefore increased
  spontaneous depolarisation of cardiac pacemaker cells.
• Decreased AV conduction — via increased vagal tone at the AV node.

---

Digoxin toxicity produces some combination of:

---

Characteristic ECG patterns include:

---

NB. Digoxin toxicity should not be confused with digoxin effect (= “sagging” ST depression and T-wave inversion in patients on therapeutic doses of digoxin; not predictive of toxicity). 

---

Clinical Pearls 

• Check for tremor artefact before you start diagnosing regularised AF!
• If the ECG pattern appears genuine and the clinical picture is
  compatible with digoxin toxicity (GI upset, xanthopsia, current digoxin
  treatment), then check an urgent digoxin level.