EKG Basics

1. Count the number of QRS complexes over a 6 second interval. Multiply by 10 to determine heart rate. This method works well for both regular and irregular rhythms. 2. Count the number of small boxes for a typical R-R interval. Divide this number into 1500 to determine heart rate

Heart Rate

The P wave represents atrial depolarization. In a normal EKG, the P-wave precedes the QRS complex. It looks like a small bump upwards from the baseline. The amplitude is normally 0.05 to 0.25mV (0.5 to 2.5 small boxes). Normal duration is 0.06-0.11 seconds (1.5 to 2.75 small boxes). The shape of a P-wave is usually smooth and rounded. P-wave questions: Are they present? Do they occur regularly? Is there one P-wave for each QRS complex? Are the P-Waves smooth, rounded, and upright? Do all P-Waves have similar shapes?

P wave

The PR Interval indicates AV conduction time. In this step you should measure the interval from where the P wave begins until the beginning of the QRS complex. Calipers, marked paper or counting small boxes methods can be used to determine PR Intervals. Normally this interval is 0.12 to 0.20 seconds (3 to 5 small boxes) in adults, longer in elderly people. This interval shortens with increased heart rate. Also evaluate if PR Intervals are constant or varying across the EKG strip. If they vary, determine if the variations are a steady lengthening until the point where an expected QRS does not appear. PR Interval questions to address: Does the PR-Interval fall within the norm of 0.12-0.20 seconds? Is the PR-Interval constant across the ECG tracing?

PR Interval

The QRS complex indicates ventricular depolarization. Depolarization triggers contraction of the ventricles. Because of the larger tissue mass, the QRS complex is larger than the P wave. While the prototypical QRS complex consists of three wave components, one or two of these components may be missing. In this step, measure the QRS interval from the end of the PR interval to the end of the S wave. Use calipers, marking paper or by counting small boxes. Normally this interval is 0.08 to 0.10 seconds. QRS questions: Does the QRS interval fall within the range of 0.08-0.10 seconds? Are the QRS complexes similar in appearance across the ECG tracing?

QRS Complex

The QT interval represents the time of ventricular activity including both depolarization and repolarization. It is measured from the beginning of the QRS complex to the end of the T wave. Normally, the QT interval is 0.36 to 0.44 seconds (9-11 boxes). The QT interval will vary with patient gender, age and heart rate. Another guideline is that normal QT Intervals is less than half of the R-R Interval for heart rates below 100 bpm.

QT Interval

For ventricular rhythms, examine the R to R intervals on the EKG strip. Small variations of up to 10% are considered equal. For atrial rhythm, observe the P-P intervals.

Rhythm

The ST segment represents the early part of ventricular repolarization. The ST segment is the line that from the end of the QRS complex to beginning of the T wave. Normally the ST segment is flat relative to the baseline.

ST Segment

The T wave indicates the repolarization of the ventricles. It is a slightly asymmetrical waveform that follows (after a pause), the QRS complex. Take note of T waves that have a downward (negative) deflection or of T waves with tall, pointed peaks. The U-wave is a small upright, rounded bump. When observed, it follows the T-wave.

T wave