Chapter 33: Arrhythmias

BASIC RHYTHM INTERPRETATION

Electrocardiograms (ECGs) of normal infants and children are different from those of normal adults. Neonates and infants will demonstrate right ventricular (RV) dominance related to the relative hypertrophy of the RV caused by the fetal circulation. Left ventricular (LV) dominance develops over the course of childhood.

• Sequence of Interpretation: Specific order is less important than having your own systematic approach to rhythm interpretation (Figure 33-1). Here is one example:

  • Rate: Heart rate

    • Clinical Tip: Estimated HR = 300 / # of big boxes

  • Rhythm: Sinus or nonsinus

    • Clinical Tip: Normal sinus rhythm requires the presence of:

      • P before every QRS

      • Regular PR interval

      • NL P wave axis (0–90 degrees) – P wave upright in I and aVF

  • Axes: QRS axis, T wave axis. An upright wave in any given lead means the vector forces travel towards that lead.

  • Intervals: Measure the PR, QRS, QTc intervals

  • Morphology: P wave amplitude and duration, QRS amplitude and duration, presence of abnormal Q waves, ST and T wave morphology

• Telemetry: Continuous monitoring of the cardiac rhythm is standard of care in the cardiac intensive care unit (CICU)

  • Cardiac monitoring is used to identify pathologic rhythms in patients at risk for arrhythmia.

  • Real-time cardiac monitoring is not an ECG. Full interpretation of axis and morphology cannot be performed due to differences in electrode positioning compared to standard 12-lead ECG.

  • Continuous cardiac monitoring is indicated in patients who have undergone cardiac surgery; have a history of heart failure or arrhythmias; or have been admitted to the ICU for major trauma, acute respiratory failure, shock, pulmonary embolus, renal failure with electrolyte abnormalities, or toxic ingestion. Also used for monitoring in patients receiving proarrhythmic medications.

RHYTHM ABNORMALITIES

PATHOLOGIC TACHYCARDIA

• Sinus Tachycardia: An elevated heart rate for age with the rhythm still originating from the sinus node. May be caused by cardiac pathology or systemic disease. Treat underlying cause.

• Premature Beats: Premature beats are common in patients admitted to the PICU (Figure 33-2).

  • Premature atrial contractions (PACs)

    • Description: An early heartbeat caused by premature activation of atrial tissue outside of the sinus node.

    • Appearance: P wave with an abnormal morphology will occur sooner than the anticipated sinus beat. This may be obscured by the preceding T wave. The PR interval may be prolonged. If the beat is very early, the QRS complex may be abnormally wide (PAC with aberrancy) or even absent (nonconducted PAC).

    • Treatment: Usually no treatment necessary for isolated PACs.

  • Premature ventricular contractions (PVCs)

    • Description: An early heartbeat caused by premature activation of ventricular tissue.

    • Appearance: Wide QRS complex will occur sooner than the anticipated sinus beat. T wave typically points in the opposite direction. Multiple PVCs can occur at regular intervals (bigeminy, trigeminy) or ...