Nursing 105 Module E Rhythm Strips 1.How is cardiac output calculated? 2.What is an ECG? 3.What is the Primary Pacemaker of the heart? 4.The SA node fires at how many BPM? 5.What is bradycardia? Tachycardia? 6.What is the secondary pacemaker of the heart? 7.What makes up one complete cardiac cycle electrically? 8.What produces a P wave? 9.What is the duration of a normal PR interval?