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Difficulty: MediumCardiovascular System

Match the following classic electrocardiographic (ECG) findings with their most likely underlying structural or electrophysiologic pathology.

  • Diffuse ST-segment elevations with reciprocal ST depression in leads aVR and V1, accompanied by PR-segment depressionInflammation of the fibroserous sac surrounding the heart
  • Electrical alternans characterized by varying amplitudes of the QRS complex from beat to beatAccumulation of fluid in the pericardial space causing pendular motion of the heart
  • Progressive lengthening of the PR interval culminating in a non-conducted P wave and a dropped QRS complexReversible conduction block typically localized at the level of the atrioventricular node
  • Shortened PR interval, widened QRS complex, and a slurred initial upstroke of the QRS complexPresence of an accessory electrical pathway bypassing the atrioventricular node

Answer

Diffuse ST elevations pair with inflammation of the fibroserous sac (acute pericarditis). Electrical alternans pairs with fluid accumulation causing pendular motion (cardiac tamponade). Progressive PR lengthening pairs with reversible atrioventricular node block (Mobitz Type I). A shortened PR interval with a slurred upstroke pairs with an accessory electrical pathway (Wolff-Parkinson-White syndrome).
Each classic ECG finding reliably reflects a specific structural or electrophysiological disruption. Epicardial inflammation causes diffuse repolarization abnormalities. Massive pericardial fluid creates a mechanical swinging effect altering ECG voltages. AV node disease causes progressive conduction delay. Finally, an accessory pathway creates a secondary, faster route for ventricular depolarization.

Step-by-Step Solution

1
Analyze the first ECG finding: Diffuse ST elevations and PR depressions.
Identified as the pathognomonic pattern for acute pericarditis.
Widespread ST elevation without corresponding vascular territory localizing signs indicates diffuse epicardial injury from sac inflammation.
2
Analyze the second ECG finding: Electrical alternans.
Identified as a classic sign of cardiac tamponade.
The varying height of the QRS complex is a mechanical artifact created by the heart swinging closer to and further from the chest wall leads within a massive pericardial effusion.
3
Analyze the third ECG finding: Progressive PR prolongation leading to a dropped beat.
Identified as Mobitz Type I (Wenckebach) second-degree heart block.
This pattern reflects progressive fatigue and delayed conduction, which anatomically occurs at the AV node.
4
Analyze the fourth ECG finding: Short PR interval with a delta wave.
Identified as ventricular pre-excitation (Wolff-Parkinson-White syndrome).
Electrical signals bypass the AV node's normal delay via an accessory pathway, exciting the ventricles early and causing the wide, slurred QRS complex.

Key Concept

Correlation of pathognomonic electrocardiographic findings with their specific underlying cardiovascular pathophysiology.
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Topics

Cardiovascular System

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