What is the diagnosis for an ECG with a heart rate of 63 beats per minute, PR interval 122–152 ms, QRS duration 110 ms, and corrected QT interval 420–430 ms?

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ECG Diagnosis: Incomplete Right Bundle Branch Block (RBBB) or Nonspecific Intraventricular Conduction Delay

Based on the QRS duration of 110 ms in an adult, this ECG most likely demonstrates either incomplete right bundle branch block (iRBBB) or a nonspecific intraventricular conduction disturbance. 1

Analysis of ECG Parameters

Heart Rate and Rhythm

  • Heart rate of 63 bpm: Normal sinus rhythm (normal range 48-98 bpm in adults) 2

PR Interval (122-152 ms)

  • Normal PR interval: The range of 122-152 ms falls within normal limits (normal reference range 113-212 ms) 2
  • No evidence of first-degree AV block, which would require PR >200 ms

QRS Duration (110 ms) - The Key Finding

According to AHA/ACCF/HRS guidelines 1:

Incomplete RBBB is defined by:

  • QRS duration between 110-120 ms in adults (your patient has exactly 110 ms)
  • Requires additional morphologic criteria in precordial leads (rsr', rsR', or rSR' pattern in V1/V2)
  • Terminal S wave characteristics in leads I and V6

Alternative diagnosis - Nonspecific Intraventricular Conduction Disturbance:

  • If the specific RBBB morphologic criteria are not met on the actual ECG tracing
  • Defined as QRS duration >110 ms in adults without meeting criteria for complete RBBB or LBBB 1

QT/QTc Interval (420-430 ms)

  • Normal QT interval: Both uncorrected (420 ms) and corrected (430 ms) values are within normal limits
  • Normal QTc reference range: 361-457 ms (Bazett) or 359-445 ms (Fridericia) 2
  • No concern for long QT syndrome

Clinical Significance

The QRS duration of 110 ms is at the threshold for abnormality and requires morphologic assessment:

  • If typical RBBB morphology is present (rsr' in V1/V2, wide terminal S in I and V6): Diagnose as incomplete RBBB 1
  • If RBBB morphology is absent or atypical: Diagnose as nonspecific intraventricular conduction delay 1

Important Caveats:

  • Incomplete RBBB may be present in the absence of heart disease, particularly if lead V1 is recorded higher than normal position 1
  • QRS duration can be influenced by body mass index and sex (males typically have longer QRS than females) 3
  • The automated ECG measurement may have small systematic variations (±4-8 ms for QRS duration) depending on the algorithm used 4

Recommendation for Complete Diagnosis

You must review the actual ECG morphology in leads V1, V2, I, and V6 to distinguish between incomplete RBBB and nonspecific intraventricular conduction delay. Without the morphologic patterns, the most accurate diagnosis based solely on intervals is "QRS prolongation at 110 ms, consistent with either incomplete RBBB or nonspecific intraventricular conduction disturbance" 1.

All other parameters (heart rate, PR interval, QT/QTc) are normal and require no further evaluation.

References

3
Research

Electrocardiographic QRS duration is influenced by body mass index and sex.

International journal of cardiology. Heart & vasculature, 2021

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