Differential Diagnosis
- How Differential Diagnoses Are Handled
- Differential Diagnoses vs. Multiple Interpretations
Illustrative Examples
Key Takeaways
Differential Diagnosis Rules and Scoring Outcomes Summary
Interpretation Impact Summary

Differential Diagnosis

Interpreting ECGs often requires identifying more than one possible explanation for the observed features. When the available clinical or ECG information is insufficient to confirm a single definitive diagnosis, clinicians list all reasonable possibilities. This list is known as the differential diagnosis.

The ECG Quiz incorporates differential diagnoses directly into its scoring and feedback system. How differential diagnoses are treated depends on the selected Skill Level (see Skill Levels and Scoring Algorithm for details).

How Differential Diagnoses Are Handled

The ECG Quiz assigns items in the differential diagnosis as either Should or Must interpretations depending on the user’s skill level.

Skill Level	How Differential Diagnoses Are Treated
Beginning Learner	Differential diagnoses are treated as Should interpretations. Users receive credit for including them but are not penalized if they do not.
Intermediate Learner	Differential diagnoses are treated as Must interpretations. Users receive credit for including them and are penalized for omissions.
Advanced Learner	Same as Intermediate. Differential diagnoses are treated as Must, and missing any required diagnosis results in a penalty.

This structure ensures that beginners are not overwhelmed, while users at higher levels are held to the standards expected of experienced interpreters.

Differential Diagnoses vs. Multiple Interpretations

Differential diagnoses represent multiple possible explanations for a set of ECG findings.

Multiple interpretations, by contrast, represent variations in the ECG itself—for example, when a finding may or may not be present, and each possibility changes the interpretation.

See: Multiple Interpretations Explained

Illustrative Examples

Consider the ECG in Figure 1, which shows a Normal Sinus Rhythm transitioning into a Supraventricular Tachycardia. Assume the user submitted the following three diagnostic statements:

Normal Sinus Rhythm
Atrial Tachycardia
Junctional Tachycardia

Beginner Skill Level

At the Beginner Level, differential diagnoses are treated as Should interpretations.

The user:

Receives full credit for the three submitted diagnoses
Is not penalized for omitting AV Nodal Tachycardia and AV Reentrant Tachycardia
Is not penalized for not submitting Supraventricular Tachycardia

Short 3-lead telemetry strip used in the example. — Fig. 1: Figure 1 — Example ECG demonstrating Normal Sinus Rhythm transitioning to Supraventricular Tachycardia.

Beginner-level results for the example differential diagnosis. — Fig. 2: Figure 2 — Results when graded at the Beginner Skill Level.

Intermediate and Advanced Skill Levels

At the Intermediate or Advanced levels, differential diagnoses are graded as Must interpretations.

Thus, although the user receives credit for their valid submissions, they are penalized for omitting:

AV Nodal Tachycardia
AV Reentrant Tachycardia

Intermediate/Advanced-level results for the example differential diagnosis. — Fig. 3: Figure 3 — Results when graded at the Intermediate and Advanced Skill Levels.

Additional Example: Beginner User, Simplified Entry

Now suppose a Beginner user submits only:

Normal Sinus Rhythm
Supraventricular Tachycardia

Because the user is at the Beginner level:

They receive full credit
They are not penalized for omitting any other differential diagnoses

Beginner-level results when only Normal Sinus Rhythm and Supraventricular Tachycardia are submitted. — Fig. 4: Figure 4 — Beginner-level results for a simplified submission.

Key Takeaways

Differential diagnoses allow multiple possible interpretations when certainty is limited.
Differential diagnosis handling is directly linked to the user’s Skill Level.
Beginners receive supportive, low-penalty scoring.
Intermediate and Advanced users are expected to include all required components of the differential.
Differential diagnoses differ from multiple interpretations, which address uncertainty about ECG features themselves.

Differential Diagnosis Rules and Scoring Outcomes Summary

The table below summarizes how Differential Diagnosis entries are handled across the three ECG Quiz Skill Levels and how each rule affects scoring, penalties, and interpretation outcomes.

Skill Level	How Differential Diagnoses Are Treated	Credit Given for Including Dx?	Penalty for Omitting Required Dx?	Scoring Outcome
Beginning Learner	Differential diagnoses are treated as Should interpretations	Yes — user receives credit for including any item in the differential	No — omissions are not penalized	Encourages exploration; protects beginners from penalties; supports early learning
Intermediate Learner	Differential diagnoses are treated as Must interpretations	Yes — user receives credit for each correct diagnosis	Yes — omissions produce False Negatives	Requires complete differential; missing diagnoses lowers accuracy score
Advanced Learner	Differential diagnoses are treated as Must interpretations	Yes — same as Intermediate	Yes — omissions produce False Negatives, sometimes multiple	Holds user to expert-level completeness and precision; strict scoring standard

Interpretation Impact Summary

Interpretation Behavior	Beginning Level	Intermediate Level	Advanced Level
Differential items included	Credited as correct	Credited as correct	Credited as correct
Differential items missing	No penalty	Penalized	Penalized
Requirements for completeness	Partial differential acceptable	Must include all items	Must include all items
Scoring strictness	Low	Moderate	Highest
Primary educational goal	Build confidence, encourage recognition	Strengthen completeness and accuracy	Achieve expert-level precision

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