Textbook Question
The ______ is the primary pacemaker of the heart.
a. Atrioventricular node
b. sinoatrial node
c. Purkinje fiber system
d. Atrioventricular bundle
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18. The Heart
Electrical Conduction System of the Heart
Multiple Choice
What is the formula for calculating heart rate using the QRS complexes on an ECG?
A
Heart rate = 300 / number of large squares between QRS complexes
B
Heart rate = 1000 / number of milliseconds between QRS complexes
C
Heart rate = 60 / number of seconds between QRS complexes
D
Heart rate = 1500 / number of small squares between QRS complexes
Verified step by step guidance1
Understand that heart rate can be calculated using different methods based on the ECG paper speed and the measurement units used.
Identify the method you want to use: large squares, small squares, milliseconds, or seconds between QRS complexes.
For the method using large squares, count the number of large squares between two consecutive QRS complexes on the ECG. Use the formula: , where n is the number of large squares.
For the method using small squares, count the number of small squares between two consecutive QRS complexes. Use the formula: , where n is the number of small squares.
For the method using time, measure the time interval between two consecutive QRS complexes in milliseconds or seconds. Use the formula: or , where n is the time interval.
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