Waveforms, Artifacts, Dysrhythmias & Life-Threatening Arrhythmias

EKG Waveforms and Intervals

Each heartbeat produces a repeating sequence of waveforms that correspond to specific electrical events in the heart:

• P wave — atrial depolarization, the electrical trigger for atrial contraction
• QRS complex — ventricular depolarization, the electrical trigger for ventricular contraction; its much larger amplitude reflects the greater muscle mass of the ventricles compared to the atria
• T wave — ventricular repolarization, the ventricles electrically "resetting" between beats
• U wave — a small wave sometimes seen after the T wave, thought to represent repolarization of the Purkinje fibers; a prominent U wave can be associated with hypokalemia

Two intervals are measured on every strip. The PR interval, from the start of the P wave to the start of the QRS complex, is normally 0.12-0.20 second (3-5 small boxes) and reflects the time it takes the impulse to travel from the atria through the AV node to the ventricles; a PR interval outside this range signals a conduction abnormality. QRS duration is normally less than 0.12 second (under 3 small boxes). A QRS complex measuring 0.12 second or wider means the impulse is not traveling through the normal, fast bundle-branch/Purkinje pathway — a critical distinction when identifying dangerous ventricular rhythms.

Recognizing Common Artifacts

Artifact is any deflection on the tracing that does not represent true cardiac electrical activity. Recognizing the type of artifact tells the PCT how to fix it — and matters for patient safety, because artifact can visually mimic a dangerous rhythm such as ventricular tachycardia or asystole. When the cause of a chaotic-looking tracing is not obviously explained by a loose lead or patient movement, the safest action is always to check the patient directly (responsiveness, breathing, pulse) rather than assume the strip is just artifact.

Recognizing Common Rhythms

Rate and regularity are the first two things to assess on any strip, followed by whether a normal, organized P wave precedes each QRS complex.

• Normal sinus rhythm (NSR): regular rhythm, rate 60-100 bpm, a P wave before every QRS complex, PR interval 0.12-0.20 second, QRS less than 0.12 second.
• Sinus bradycardia: the same regular pattern and normal waveforms as NSR, but the rate is below 60 bpm.
• Sinus tachycardia: the same regular pattern and normal waveforms as NSR, but the rate is above 100 bpm.
• Atrial fibrillation (AFib): an irregularly irregular rhythm with no identifiable, organized P waves — instead a chaotic, fibrillatory baseline — and a ventricular (QRS) response that is irregular in timing; AFib is common and not immediately life-threatening on its own, but it is clinically significant because it increases stroke risk and should always be reported to the care team.

Life-Threatening Arrhythmias — Immediate Recognition and Response

Some rhythms require the PCT to act immediately, because they represent a direct threat to the patient's circulation and survival:

• Ventricular tachycardia (VT): a wide (0.12 second or greater), regular, fast rhythm — typically 100-250 bpm — originating in the ventricles rather than following the normal conduction pathway. VT may still produce a pulse, but it can rapidly deteriorate into a pulseless rhythm or ventricular fibrillation, so a rapid pulse check is a required part of confirming the patient's status whenever a wide-complex tachycardia is seen — it should never be assumed benign on the tracing alone.
• Ventricular fibrillation (VF): a chaotic rhythm with no organized, identifiable QRS complexes at all — the ventricles are quivering rather than contracting, so there is no cardiac output and no pulse. VF is always a cardiac arrest. It may appear coarse (larger, more visibly chaotic waves) or fine (low-amplitude, nearly flat chaotic activity); both are the same lethal rhythm and both demand the identical emergency response.
• Asystole: a "flatline" with no discernible electrical activity; it must be confirmed in more than one lead before being called.

When a PCT observes VT, VF, or any sign of cardiopulmonary compromise — pulseless, unresponsive, not breathing normally — the PCT must immediately report it and initiate Basic Life Support (BLS), beginning chest compressions and calling for the code team or emergency response, without waiting for a physician order. For VF or pulseless VT, current resuscitation guidance calls for immediate high-quality CPR combined with defibrillation as soon as an AED or defibrillator is available; asystole and other non-shockable rhythms are instead managed with continued CPR and medications rather than defibrillation. Noting the exact time the dysrhythmia was first observed is also important, since that timestamp becomes part of the code documentation and helps the resuscitation team track elapsed time without effective circulation. While full rhythm interpretation is ultimately performed by a physician or credentialed EKG specialist, the CPCT/A's role is to recognize the pattern fast enough to trigger a life-saving response — hesitation or uncertainty about the exact rhythm name should never delay the call for help. Recognizing these rhythms and reacting within seconds, not minutes, is one of the most important patient-safety responsibilities of the CPCT/A role.