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Cardiac Conduction – Identifying Rhythms

Cardiac Conduction – Identifying Rhythms.

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Cardiac Conduction – Identifying Rhythms

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  1. Cardiac Conduction – Identifying Rhythms

  2. Because ECG paper moves at a standardized 25mm/sec, the vertical lines can be used to measure time. There is a 0.20 sec between 2 of the large lines. Therefore, if you count the number of heart beats (QRS complexes) in between 30 large boxes (6 seconds) and multiply by 10, you have beats per minute. Conveniently, ECG paper usually has special markings every 3 seconds so you don't have to count 30 large boxes. There is, however, an easier and quicker way to estimate the heart rate. As seen in the diagram below, when QRS complexes are 1 box apart the rate is 300 bpm. 2 boxes apart...150 bpm, etc. So if you memorize these simple numbers you can estimate the heart rate at a glance!

  3. Determining Heart Rate and Rhythm The EKG paper is made of a grid of big boxes and small boxes. The EKG paper is made of a grid of big boxes and small boxes. Each big box is 10 mm in length has five small boxes and is 0.20 sec. Each small box is 1 mm and represents 0.04 sec.The EKG paper moves at a standard speed of 25 mm/sec. At standard speed, the heart rate can be determined by either of the following methods. • Method I • Examine the distance between QRS complexes and determine if the peaks (RR intervals) are regularly spaced.  • The EKG below shows regular RR intervals. If the RR distances are regular, count the number of "small boxes" from the beginning of one QRS complex to the beginning of the next QRS complex. Then divide 1500 by the number of "small boxes" to obtain the heart rate in beats per minute.

  4. Method I (cont) The EKG on the bottom right shows irregularly spaced RR intervals. If the distances are irregular, count the number of QRS complexes within 30 large boxes (which each represent 0.2 seconds) and multiply this number by 10 to obtain the heart rate in beats/minute.

  5. Method II If the peaks are regular, the heart rate can be estimated using the EKG grid. To do this locate a QRS complex on a bold line. If the next QRS complex is separated by: i. One large box, the heart rate is 300 BPM (300/1) ii. Two large boxes, the heart rate is 150 BPM (300/2) iii. Three large boxes, the heart rate is 100 BPM (300/3) iv. Four large boxes, the heart rate is 75 BPM (300/4)                                                                         ...and so on. • The EKG grid used to rapidly estimate the heart rate

  6. The difference between Atrial and Ventricular Rates The heart rate calculated using the RR intervals is the ventricular rate. In sinus rhythm, the ventricular rate corresponds to the atrial rate. The atrial rate can be determined from the PP interval using either of the two methods above.

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