Intervals and waveforms

EKG Overview

  • Each waveform, interval, and segment on an EKG has significant meaning.

  • Distinguish between normal and abnormal tracings.

  • Understand the value of EKG paper blocks when interpreting intervals.

  • Cardiac cycle starts at the beginning of the T wave and ends at the end of the T wave.

Key Waveform Components

P Wave

  • Represents atrial depolarization; begins when the SA node fires, leading to atrial contraction.

  • Normal P waves have a positive deflection and should occur prior to each QRS.

  • Variations in shape or absence can indicate electrical conduction pathway abnormalities.

QRS Complex

  • Represents ventricular depolarization, leading to ventricular contraction.

  • Atrial repolarization occurs simultaneously but is not visible on the EKG.

  • Normal QRS interval ranges from 0.04 to 0.10 seconds.

  • Evaluate consistency and height of the QRS complexes; abnormalities indicate potential ventricular dysfunction.

  • J Point is where ventricular depolarization stops and repolarization begins; important during myocardial ischemia.

T Wave

  • Represents ventricular repolarization; follows each QRS with a brief pause at J Point.

  • T waves should appear uniform and consistent.

  • U wave (if visible) indicates repolarization of the bundle of His and Purkinje fibers; small upward curve.

  • Electrolyte imbalances may cause the appearance of U waves.

Key Intervals

PR Interval

  • Time from SA node firing to ventricular depolarization; reflects atrial activity.

  • Measured from the beginning of one P wave to the beginning of the next.

  • Important for analyzing rate and rhythm.

RR Interval

  • Time between consecutive R waves; useful in rhythm and rate analysis.

  • Measured from the beginning of one R wave to the next.

QT Interval

  • Represents one complete ventricular cycle (depolarization and repolarization).

  • Measured from the beginning of the Q wave to the end of the T wave.

PR Segment

  • Time between end of P wave and beginning of Q wave; shows conduction through AV node.

ST Segment

  • Early phase of ventricular repolarization, important for identifying ischemia.

  • Measured from the end of S wave to the beginning of T wave.

Waveform Characteristics

  • Analyze direction, symmetry, and configuration of waveforms on EKG.

P Wave Characteristics

  • Should be symmetrical and positive deflection (above baseline).

  • QRS complex should follow each P wave, indicating normal conduction.

T Wave Characteristics

  • Look for symmetry and consistency; should peak toward the end and match QRS direction.

Pathway Concerns and External Factors

  • Abnormalities in P waves and PR intervals indicate atrial dysfunction.

  • QRS and T wave abnormalities indicate ventricular dysfunction.

  • External factors (e.g., electrolyte levels, medications) and patient conditions can affect EKG readings.

  • Example: High potassium slows heart rate; low potassium causes abnormal rhythms.

  • Important to gather comprehensive medical and medication history for accurate analysis.