![]() A heart rate larger than 100 is called tachycardia.A heart rate less than 60 is called bradycardia.Multiply this number by 20 to find the number of beats/minute. Count the number of QRS complexes that fit into 3 seconds (some ECG writers print this period on the ECG paper).The ECG paper runs at 25 mm/sec through the ECG printer therefore heart rate can be calculate using the following formula:.When the second QRS complex is between two lines, take the mean of the two numbers from the sequenceīelow is an image showing the squares counting method used to calculate the heart rate. ![]() Stop the sequence at the next QRS complex. Count from the first QRS complex, the first thick line is 300, the next thick line 150 etc. Determining the heart rate can be done using one of these three methods:.See the picture below for a detailed explanation:īelow is an image showing the significance of small and large squares in an ECG paper. It is important to remember the temporal significance of the small and large squares on an ECG strip.The normal heart rate is between 60 and 100 beats per minutes.When the rhythm is irregularly irregular it is a sign of the presence of atrial fibrillation. When the RR interval is not constant, the rhythm is said irregular.Variable morphologies of P waves in a single ECG lead is suggestive of an ectopic pacemaker rhythm such as wandering pacemaker or multifocal atrial tachycardia.P wave is absent in atrial fibrillation, junctional or ventricular rhythm.The distance between two R waves, called RR interval, is constant in a regular rhythm.The P wave duration is usually shorter than 0.12 seconds.The P wave is positive in II and aVF, and biphasic in V1.The maximal height of the P wave is 2.5 mm in leads II and/or III.The frequency ranges between 60 and 100 beats per minuteīelow is an ECG showing normal sinus rhythm.The rhythm is regular, but varies slightly while breathing.The P waves maximum height is 2.5 mm in II and/or III.The P wave is positive in I and II, and biphasic in V1.A P wave (atrial contraction) precedes every QRS complex.Then the depolarization wave spreads to the cells of the left atrium, the AV node, the bundle of His and then to the ventricles through the purkinje fibers.Ĭriteria for normal sinus rhythm (see also Basics) When the sinus node generates an electrical impulse, the surrounding cells of the right atrium depolarize. The sinus node (SA), located in the roof of the right atrium, is the fastest physiological pacemaker.Compare the current ECG to previous ECG.Each ECG should be evaluated for the following: The interpretation of an ECG should be done in a consistent step-by-step way.Assistant Editor(s)-in-Chief: Rim Halaby Overview
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