Question

AAAAA Label P. QRS, and Twaves on the ECG strip in Figure 4.5. Figure 1.5: ECG strip. DETERMINE HEART RATE FROM AN ECG The range of normal heart rates is called normal sinus rhythm (NSR). In an average adult NSR is between 60 and 100 bpm. A heart rate below 60 bpm is called bradycardia. However, a highly acro bically conditioned persons often have a normal heart rate below 60 bpm. A heart rate above 100 bpm in an adult is called tachycardia. But it is normal for the heart rate of a young child to be above 100 bpm. While neither bradycardia or tachycardia is desirable, in both these conditions the heart is still effectively pumping blood. On the other hand, in ventricular fibrillation, the individual care diac muscle cells in the ventricles are beating independently of each other. This produces a quivering motion rather than a coordinated contraction that can not effectively pump blood throughout the body. This is a medical emergency. An ECG strip can be used to calculate heart rate. ECGs are printed on strips of paper with 1 mm square lines that moves at a speed of 25 mm/sec. As a result each 1 mm square represents 0.04 sec- onds. To calculate heart rate using an ECG strip: 1. Locate the top of an Rwave. Count the number of squares between this wave and the next Rwave. This gives you the distance in mm of one heart beat (mm/1 beat). 2. Multiply the number of squares by 0.04 sec to give the time in seconds of one heart beat (sec/1 beat). Since this is the time for 1 heart beat, it is the length of one cardiac cycle (CC). 3. Finally, convert this number from sec/1 beat to beats/minute by dividing 60 by the answer in step 2 For example: 1. You count 14 small squares between two Rwaves = 14 mm. 2. 0.04 sec X 14 mm = 0.6 sec/beat 3. 60 sec/min + 0.6 sec/beat = 100 beats/min Determine the cardiac cycle and heart rate for each ECG tracing in Figure 4.6. Exercise 4. Heart Rat, Blood P r

Answer 1

A.

There is 28 small square in between RR wave, so

Cardiac Cycle - 1.12 sec/beat

Heart Rate - 54 beats/min

It is bradycardia

B.

There is 17 small square in between RR wave, so

Cardiac Cycle - 0.68 sec/beat

Heart Rate - 88 beats/min

It is Normal Sinus rhythm

C.

This image shows Ventricular fibrillation(VF)

We can not calculate HR from a VF ECG because there is no RR interval present.

D.

There is 11 small square in between RR wave, so

Cardiac Cycle - 0.44 sec/beat

Heart Rate - 136 beats/min

It is Trachycardia