Monday, January 22, 2024

EMS Cardiology - EKG Rhythms

EMS providers play a crucial role in identifying and managing various cardiac rhythms in the prehospital setting.

An EKG (electrocardiogram) rhythm refers to the pattern of electrical activity in the heart as recorded by an electrocardiogram.

An electrocardiogram is a medical test that measures the electrical impulses generated by the heart during each heartbeat.

It is commonly used to diagnose and monitor various heart conditions. Understanding the components of an EKG rhythm is essential for accurate interpretation.

The EKG rhythm is graphically represented on paper or a monitor, illustrating the different phases of the cardiac cycle.

The typical EKG waveform includes P waves, QRS complexes, and T waves, which correspond to specific electrical events in the heart.

Here are the key components and some common abnormal rhythms:

Key Components of EKG Rhythm:

P Waves:

Normal: Represents atrial depolarization (contraction).

Shape: Typically upright and rounded.

Duration: Normally 0.06 to 0.12 seconds.

Abnormalities: Absent P waves, inverted P waves, or abnormal shapes may indicate atrial issues.

QRS Complex:

Normal: Indicates ventricular depolarization (contraction).

Shape: Typically narrow (0.06 to 0.10 seconds).

Duration: Abnormally wide QRS complexes may indicate ventricular conduction abnormalities.

Abnormalities: Wide QRS (e.g., bundle branch blocks) or absence of QRS (asystole) are concerning findings.

T Waves:

Normal: Represents ventricular repolarization (relaxation).

Shape: Usually upright and rounded.

Abnormalities: Inverted T waves or changes in T-wave morphology may indicate ischemia, electrolyte imbalances, or other cardiac issues.

PR Interval:

Normal: Represents the time from atrial depolarization to ventricular depolarization.

Duration: Normal PR interval is 0.12 to 0.20 seconds.

Abnormalities: Prolonged PR interval may indicate heart block.

QT Interval:

Normal: Represents the total time for ventricular depolarization and repolarization.

Duration: Corrected QT interval (QTc) is influenced by heart rate.

Abnormalities: Prolonged QT interval may predispose to ventricular arrhythmias.

Heart Rate:

Normal: Adult resting heart rate is 60 to 100 beats per minute.

Abnormalities: Tachycardia (heart rate >100 bpm) or bradycardia (heart rate <60 bpm) may indicate various cardiac conditions.

The pattern and timing of these waves help healthcare professionals assess the heart's electrical activity and identify any abnormalities in the rhythm.

Normal EKG rhythms provide information about the regular and coordinated functioning of the heart, while abnormal rhythms, such as atrial fibrillation, ventricular tachycardia, or bradycardia, can indicate various heart conditions.

Common Abnormal Rhythms:

Atrial Fibrillation (AFib):

Irregularly irregular rhythm.

Absence of distinct P waves.

Chaotic, fibrillatory baseline.

Atrial Flutter:

Regular or irregular rhythm with sawtooth-shaped P waves.

Atrial rate is often faster than the ventricular rate.

Ventricular Tachycardia (VTach):

Regular, wide QRS complexes (>0.12 seconds).

Often associated with hemodynamic instability.

Ventricular Fibrillation (VFib):

Chaotic, irregular waveform with no organized QRS complexes.

Emergency situation requiring immediate defibrillation.

Supraventricular Tachycardia (SVT):

Narrow QRS complexes with a rapid heart rate.

Regular or slightly irregular rhythm.


Absence of any discernible electrical activity.

Considered a medical emergency requiring CPR and advanced life support interventions.


Heart rate <60 bpm

May be associated with heart blocks or intrinsic conduction system issues.

Clinical Considerations:

Ischemia: ST-segment elevation or depression may indicate myocardial ischemia.

Conduction Blocks: Bundle branch blocks or heart blocks may affect the QRS complex and PR interval.

Medication Effects: Some medications can affect the EKG, leading to QT prolongation or other abnormalities.

EMS providers should receive regular training in EKG interpretation to enhance their ability to recognize and respond to abnormal rhythms promptly.

Additionally, collaboration with medical control and receiving hospitals is essential for optimal patient care in the prehospital setting.

Further Reading:

Garcia, T. (2013) 12-Lead ECG: The Art of Interpretation (2nd Ed.) Jones & Bartlett Learning

Walraven, G. (2016) Basic Arrhythmias (8th Ed.). Pearson 

ECG Educational Standards for Prehospital Providers Accessed January 22, 2024

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