Final answer:
Anna had a pacemaker implanted to regulate her heart rate, which is necessary when dealing with arrhythmias. Pacemakers send electrical impulses to the heart and adjust the heart rate in response to physical activity. Therefore, the correct option is 1.
Step-by-step explanation:
Anna had a pacemaker implanted to regulate her heart rate. Pacemakers are medical devices designed to send electrical impulses to the heart muscle, ensuring that it continues to contract and pump blood effectively. These devices can correct arrhythmias, which are problems with the rate or rhythm of the heartbeat. If the heart rhythm is too fast (tachycardia) or too slow (bradycardia), pacemakers can stabilize it. The device has sensors that detect body motion and breathing to increase the heart rate during physical activities to meet the body's increased need for blood and oxygen.