ECG Interpretation for Nurses
Chapter 1: The Five-Step System for Every Strip Every rhythm strip, from the simplest to the most frightening, is read with the same five steps, and using them in order is what separates systematic reading from guessing. Step one: rate. Count the R waves in a six-second strip and multiply by ten, or use the large-box method, dividing 300 by the number of large boxes between R waves; normal is 60 to 100. Step two: rhythm. Measure whether the R-to-R intervals are regular or irregular. Step three: P waves. Confirm there is one upright P wave before every QRS complex. Step four: PR interval. Measure it; normal is 0.12 to 0.20 seconds, three to five small boxes. Step five: QRS complex. Measure it; normal is under 0.12 seconds, three small boxes. The power of the system is that each abnormal finding points to a short list of rhythms. A fast rate with a narrow QRS is a supraventricular problem. A fast rate with a wide QRS is ventricular until proven otherwise. No P waves with an irregularly irregular rhythm is atrial fibrillation. No P waves with a regular fast rate is a junctional or supraventricular tachycardia. You do not need to memorize forty rhythms; you need the five measurements and the short list each combination produces.
Paper speed and calibration Standard ECG paper runs at 25 millimeters per second, so each small box is 0.04 seconds and each large box, five small boxes, is 0.20 seconds. Thirty large boxes make a six-second strip, which is why counting R waves in thirty large boxes and multiplying by ten gives the rate. Calibration is set so ten millimeters equals one millivolt, and a calibration mark at the start of the tracing confirms it. If the paper speed or calibration differs, every measurement changes, so checking these two settings is the silent first step before the five formal ones. Using the large-box method, an R-R interval spans four large boxes. What is the heart rate? A. 60 bpm B. 75 bpm C. 100 bpm D. 150 bpm Answer: B. Three hundred divided by four large boxes equals 75 beats per minute. The large-box method divides 300 by the number of large boxes between R waves.
Which QRS width is within normal limits? A. 0.08 seconds B. 0.14 seconds C. 0.16 seconds D. 0.20 seconds Answer: A. A normal QRS is under 0.12 seconds. A width of 0.08 is normal; the wider values indicate delayed ventricular conduction such as a bundle branch block or a ventricular rhythm.; Chapter 2: Sinus Rhythms: Normal, Fast, and Slow; ECG Interpretation for Nurses
ECG Interpretation for Nurses
calcium channel blockers, or digoxin, plus anticoagulation, is the standard management. Atrial flutter shows a sawtooth baseline of flutter waves, typically at an atrial rate near 300, with the ventricles responding at a regular fraction of that rate, often 150 with two-to-one conduction. A regular narrow-complex rhythm at exactly 150 should always make you suspect flutter. Like fibrillation, flutter carries clot risk and is anticoagulated, and it is often treated with ablation of the flutter circuit. Supraventricular tachycardia is a sudden, regular, narrow-complex tachycardia, usually 150 to 250, that starts and stops abruptly. The patient feels palpitations, may be lightheaded, and is usually stable enough for vagal maneuvers first: bearing down as if having a bowel movement, or coughing. If those fail, adenosine is given rapid push with a fast flush, and the patient is warned about the brief flushing and chest pressure. Unstable SVT, with hypotension or chest pain, goes straight to synchronized cardioversion. Rhythm
Baseline; Regularity; Key treatment; Atrial fibrillation; Chaotic, no P waves; Irregularly irregular; Rate control plus anticoagulation; Atrial flutter; Sawtooth flutter waves; Regular response; Rate control, ablation, anticoagulation; P waves buried; Regular, 150-250; Vagal maneuvers, then adenosine
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