Digoxin Effect

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 Features demonstrating the Digoxin Effect

Other Digoxin effect features

Additional ECG Features

• 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)

QRS complex / ST segment changes

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 (our personal favourite) “Salvador Dali’s moustache”!

T-wave changes

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

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

Advanced Reading

Online

• Wiesbauer F, Kühn P. ECG Yellow Belt online course: Become an ECG expert. Medmastery
• Wiesbauer F, Kühn P. ECG Blue Belt online course: Learn to diagnose any rhythm problem. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.

Textbooks

• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Hampton J. The ECG Made Practical 7e, 2019
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography 1e, 2009
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Mattu A, Brady W. ECG’s for the Emergency Physician Part I 1e, 2003 and Part II
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest