Digoxin Effect

Electrocardiographic Features

Digoxin effect refers to the presence on the ECG of:

• Downsloping ST depression with a characteristic “sagging” appearance (see below).
• Flattened, inverted, or biphasic T waves.
• Shortened QT interval.

Other features of digoxin effect

• Mild PR interval prolongation of up to 240 ms (due to increased vagal tone).
• Prominent U waves.
• Peaking of the terminal portion of the T waves.
• J point depression (usually in leads with tall R waves).

The morphology of the QRS complex / ST segment is variously described as either “slurred”, “sagging” or “scooped” and resembling either a “reverse tick”, “hockey stick” or (my personal favourite) “Salvador Dali’s moustache”!

The most common T-wave abnormality is a biphasic T wave with an initial negative deflection and terminal positive deflection. This is usually seen in leads with a dominant R wave (e.g. V4-6). The first part of the T wave is typically continuous with the depressed ST segment. The terminal positive deflection may be peaked, or have a prominent U wave superimposed upon it. 

Mechanism

The ECG features of digoxin effect are seen with therapeutic doses of digoxin and are due to:

• Shortening of the atrial and ventricular refractory periods — producing a short QT interval with secondary repolarisation abnormalities affecting the ST segments, T waves and U waves.
• Increased vagal effects at the AV node — causing a prolonged PR interval.

NB. The presence of digoxin effect on the ECG is not a marker of digoxin toxicity. It merely indicates that the patient is taking digoxin.

 ECG Examples

Example 1

Digoxin effect:

• This is the classic picture of digoxin effect with the “sagging” ST segments and T waves taking on the appearance of “Salvador Dali’s moustache”.

 

Example 2

Digoxin effect:

• Sagging ST segments are most evident in the lateral leads V4-6, I and aVL.

 

Example 3

Another example of digoxin effect:

• The sagging morphology is most evident in V6 and in the lead II rhythm strip.

 

Example 4

This is a slight variation on the classic digoxin pattern:

• There is still downsloping ST depression but it is slightly more angular, in comparison to the “sagging” ST segments from the previous example.
• Also, there is J-point depression in V4-6, which mimics the appearance of left ventricular hypertrophy.
• The short QT interval, the “sagging” appearance in the inferior leads and the lack of voltage criteria for LVH indicates that this is digoxin effect rather than LVH.

 

Example 5

Digoxin effect:

• Sagging ST depression is clearly evident in leads I, II, III, aVF and V5-6.
• Frequent premature ventricular complexes (PVCs) suggest the possibility of digoxin toxicity.

 

Related Topics

• Digoxin toxicity
• The QT interval

Further Reading

• ECG BASICS – Waves, Intervals, Segments and Clinical Interpretation
• ECG CLINICAL CASES – Your favourite ECG’s placed in clinical context with a challenging Q&A approach
• ECG and Cardiology Eponymous Syndromes – Cheats guide to eponymous emancipation
• ECG Reference Sites on the WEB – the best of the rest

Author Credits