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Difficulty: MediumCardiovascular System

Match the following cardiac arrhythmias and conduction disorders with their characteristic electrocardiogram (ECG) findings.

  • Multifocal atrial tachycardiaAt least three morphologically distinct P waves in a single lead with an irregular R-R interval
  • Wolff-Parkinson-White syndromeShortened PR interval, widened QRS complex, and a slurred initial upstroke of the QRS
  • Mobitz type I second-degree atrioventricular blockProgressive lengthening of the PR interval followed by a nonconducted P wave
  • Third-degree atrioventricular blockRegular P-P and R-R intervals with completely independent atrial and ventricular rates

Answer

Multifocal atrial tachycardia corresponds to multiple distinct P waves. Wolff-Parkinson-White syndrome corresponds to a short PR interval and delta wave. Mobitz type I corresponds to progressive PR lengthening before a dropped beat. Third-degree block corresponds to independent but regular P-P and R-R intervals.
Each rhythm disorder has a highly specific electrocardiographic signature based on its underlying electrophysiological mechanism, as detailed in the correct pairings.

Step-by-Step Solution

1
Identify the distinguishing ECG feature for multifocal atrial tachycardia (MAT).
MAT requires the presence of three or more distinct P-wave morphologies in the same lead.
The rhythm originates from multiple competing ectopic foci in the atria, causing variations in atrial depolarization pathways.
2
Identify the distinguishing ECG feature for Wolff-Parkinson-White (WPW) syndrome.
WPW is characterized by a short PR interval, a wide QRS complex, and a delta wave (slurred upstroke).
An accessory pathway bypasses the AV node's natural delay, causing premature ventricular depolarization.
3
Identify the distinguishing ECG feature for Mobitz type I second-degree AV block.
Mobitz type I exhibits progressive lengthening of the PR interval until a QRS complex is dropped.
This occurs due to progressive fatigue and delayed conduction through the AV node.
4
Identify the distinguishing ECG feature for third-degree (complete) AV block.
Third-degree AV block shows completely dissociated P waves and QRS complexes.
There is a complete failure of conduction, forcing the atria and ventricles to rely on separate, independent pacemakers.

Key Concept

Identifying characteristic electrocardiogram (ECG) patterns for arrhythmias and conduction blocks is essential for accurate diagnosis and management.
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Topics

Cardiovascular System

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