Chapter 25: Diagnostic Criteria

INTRODUCTION

In this chapter you will find the criteria for most of the electrocardiographic diagnoses that you are likely to encounter in clinical practice and on board exams. Minor variations of these criteria have been published.

ELECTROCARDIOGRAPHIC DIAGNOSES

I. RHYTHM ABNORMALITIES

A. Supraventricular Rhythms and Complexes

Sinus rhythm

• P wave of sinus origin.

  • Normal P wave configuration (upright in leads I, II, and aVF, and inverted in aVR).

  • Normal mean axis (between 0 and +75 degrees).

• Normal PR interval (0.12-0.20 seconds).

• Consistent P wave configuration and PR interval in each lead.

• Constant P-P cycles with only minor variation.

  • Any variation between the longest and shortest cycles is ≤0.12 seconds or ≤10%.

• HR of 60 to 100 bpm.

Sinus bradycardia

• Normal sinus rhythm except for heart rate.

• HR <60 bpm.

  • Comment: Some authors define it as <50 bpm.

Sinus tachycardia

• Normal sinus rhythm except for heart rate.

• HR >100 bpm.

Sinus arrhythmia

• P wave of sinus origin with normal P wave morphology and axis.

• Normal HR.

• Phasic variability of P-P intervals.

• P-P intervals vary from the shortest to longest cycle by either:

  • >0.12 seconds.

  • >10%.

    • – Determine this percentage by dividing the difference between the two numbers by the average of the two numbers, then multiplying by 100 to convert to percent.

      • - Difference between the two numbers: (Maximum P-P interval − Minimum P-P interval).

      • - Average of the two numbers: (Maximum P-P interval + Minimum P-P interval) ÷2.

    • – Comment: The cycles used in the above calculation do not need to be consecutive.

• Sinus arrhythmia may be further characterized as respiratory, nonrespiratory, ventriculophasic, and combined with bradycardia (sinus bradyarrhythmia).

Sinus arrest or pause

• Sinus rhythm with sudden absence of P waves at the expected time/cycle.

• P waves and QRS complexes are absent during the pause (except for the emergence of a subsidiary pacemaker).

• The resulting pause is not an exact multiple of the normal cycle length.

Sinoatrial exit block

An abnormality of transmission of the sinus impulse that results in a delay or failure to produce a P wave. Only second-degree SA block can be identified on the surface ECG. Second-degree SA block may manifest in two forms, type I and type II.

Type I second-degree SA block