Digitalis effect
Digitalis effect
Digoxin effect on the ECG of:
Downsloping ST depression with a characteristic “reverse tick” or “Salvador Dali sagging” appearance
Flattened, inverted, or biphasic T waves
Shortened QT interval
Flattened, inverted, or biphasic T waves
Shortened QT interval
1. Which ECG change is most characteristic of the digitalis effect?
Digitalis produces a sagging “hockey-stick” ST depression.
2. Digitalis effect is most prominent in which leads?
The digitalis effect is most striking in lateral leads.
3. What happens to the QT interval in digitalis effect?
Digitalis shortens QT interval due to accelerated repolarization.
4. Which T wave abnormality is typical of digitalis effect?
Digitalis often flattens or mildly inverts T waves.
5. PR interval in digitalis effect is usually:
Vagal action of digitalis causes PR prolongation.
6. Digitalis effect should not be mistaken for:
The ST depression of digitalis may mimic ischemia.
7. Which arrhythmia is most characteristic of digitalis toxicity?
Paroxysmal atrial tachycardia with block is classic for digitalis toxicity.
8. The “reverse tick” or hockey-stick appearance is due to:
The sagging ST depression produces the “reverse tick mark” pattern.
9. Which electrolyte imbalance enhances digitalis toxicity?
Hypokalemia increases digitalis binding to Na⁺/K⁺-ATPase, enhancing toxicity.
10. Digitalis effect is best described as:
It is a drug effect, not due to ischemia or pre-excitation.
11. Digitalis increases which ECG interval due to vagal tone?
Digitalis enhances AV nodal delay, prolonging PR interval.
12. Which part of the ECG is most influenced by digitalis?
Digitalis has its most characteristic effects on the ST segment.
13. Which feature helps distinguish digitalis effect from ischemia?
The scooped downsloping ST is specific for digitalis.
14. Digitalis effect on QRS duration is usually:
Digitalis effect does not widen QRS.
15. Digitalis is known to suppress which conduction abnormality?
Vagal effect of digitalis slows AV nodal reentry.
16. Which ECG sign indicates severe digitalis toxicity?
Bidirectional VT is pathognomonic of severe digitalis toxicity.
17. Digitalis effect is best categorized as:
It is a drug effect, not due to ischemia or electrolyte imbalance.
18. The presence of digitalis effect indicates:
Digitalis effect occurs at therapeutic levels; toxicity shows arrhythmias.
19. Which rhythm abnormality is strongly suggestive of digitalis toxicity?
Atrial tachycardia with block is highly characteristic of toxicity.
20. Which of the following is NOT typical of digitalis effect?
Digitalis does not cause ST elevation; that suggests MI or pericarditis.
| No. | Digitalis effect -Key Point |
|---|---|
| 1 | Digitalis effect produces characteristic scooped ST segment depression (“hockey-stick”). |
| 2 | Seen best in lateral leads (V4–V6, I, aVL). |
| 3 | QT interval is shortened due to accelerated repolarization. |
| 4 | PR interval may be prolonged due to vagal stimulation. |
| 5 | T waves often flattened or inverted in affected leads. |
| 6 | Digitalis effect is dose-dependent and more marked at higher serum levels. |
| 7 | Not indicative of ischemia despite ST depression morphology. |
| 8 | Helps differentiate digitalis effect from ischemic ST changes. |
| 9 | More prominent when potassium levels are low (hypokalemia). |
| 10 | Can coexist with arrhythmias caused by digoxin toxicity. |
| 11 | May mimic “strain” pattern in LV hypertrophy. |
| 12 | QT shortening is a hallmark distinguishing from most other drug effects. |
| 13 | ECG changes are reversible with discontinuation of drug. |
| 14 | Degree of ST scooping does not correlate well with toxicity. |
| 15 | Digitalis effect itself is benign, unlike digoxin toxicity arrhythmias. |
| 16 | Common in patients with chronic digoxin therapy for heart failure or AF. |
| 17 | Pseudonormalization of ST-T changes may signal toxicity onset. |
| 18 | Distinction from ischemia: concave scooping vs convex ST depression. |
| 19 | Rate of digitalis uptake affects prominence of ECG changes. |
| 20 | ECG monitoring is crucial in patients on digoxin, especially elderly or renal dysfunction cases. |
Q1. What is the hallmark ECG feature of digitalis effect?
A: Scooped ST segment depression (hockey-stick appearance).
Q2. In which leads is the digitalis effect most prominent?
A: Lateral leads (V4–V6, I, aVL).
Q3. What happens to the QT interval in digitalis effect?
A: It becomes shortened.
Q4. Does digitalis effect prolong or shorten PR interval?
A: It can prolong PR interval due to vagal action.
Q5. How do T waves change in digitalis effect?
A: They may flatten or invert.
Q6. Does digitalis effect imply ischemia?
A: No, ST depression here is non-ischemic.
Q7. What electrolyte imbalance enhances digitalis ECG changes?
A: Hypokalemia.
Q8. Are ECG changes of digitalis effect permanent?
A: No, they are reversible on drug withdrawal.
Q9. What is the difference between digitalis effect and digoxin toxicity?
A: Effect = benign ECG changes, Toxicity = arrhythmias and conduction blocks.
Q10. Which patient groups need closer ECG monitoring while on digoxin?
A: Elderly, renal impairment, and those with electrolyte disturbances.
| Feature | Digitalis Effect (Therapeutic, expected ECG change) | Digitalis Toxicity (Pathological, dangerous) |
|---|---|---|
| Definition | Predictable ECG changes seen at normal therapeutic digoxin levels | Adverse cardiac/electrolyte disturbances due to toxic levels of digoxin |
| ST Segment | Downsloping, scooped ST depression (“reverse tick mark”) | May show further ST depression with additional arrhythmias |
| T Waves | Flattened or inverted, nonspecific | Deeply inverted, biphasic, or bizarre morphology possible |
| PR Interval | Mild prolongation (↑ AV nodal conduction delay) | Marked prolongation; may lead to AV block |
| QT Interval | Shortened (due to faster ventricular repolarization) | Variable; may be normal, shortened, or with abnormal U waves |
| P Waves | No significant abnormality | Atrial tachycardia, atrial fibrillation, or absent (with AV block) |
| Arrhythmias | None (effect only, no arrhythmia) | Atrial tachycardia with block, ventricular tachycardia, bidirectional VT (classical), VF |
| Conduction Abnormalities | First-degree AV block only (benign) | Second- or third-degree AV block, sinus arrest, ventricular arrhythmias |
| Heart Rate | Normal or slightly decreased (due to vagotonia) | Bradycardia, tachycardia, or alternating brady-tachy syndrome |
| Serum Digoxin Level | Within therapeutic range (0.5–2 ng/mL) | Elevated >2 ng/mL (but toxicity can occur even at therapeutic levels) |
| Electrolyte Influence | Normal ECG if potassium normal | Hypokalemia, hypercalcemia, or hypomagnesemia predispose to toxicity |
| Symptoms | None (ECG finding only) | Nausea, vomiting, visual disturbances (yellow/green halos), confusion |
| Reversibility | Harmless and expected; not dose-limiting | Potentially fatal; requires urgent management |
| Diagnostic Importance | Helps confirm patient is on digoxin | Identifies life-threatening complication |
| Prognosis | Benign, not associated with adverse outcomes | Dangerous; high risk of sudden cardiac death |
| Management | No treatment needed | Stop digoxin, correct electrolytes, give Digibind (antibody Fab) if severe |
| Clinical Significance | Marker of digoxin therapy, not pathology | Emergency diagnosis needing immediate therapy |
| ECG Misinterpretation Risk | Can mimic ischemia (ST depression) | Can mimic any arrhythmia; needs high suspicion |
| Key Teaching Point | Digitalis effect = ECG marker of therapy | Digitalis toxicity = arrhythmias + systemic features |
