Part 1: Review the sections entitled Cardiac Cycle and Heart Sounds in Chapter 15 of the textbook. Answer the questions below.

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1 Name: Anatomy & Physiology Cardiac Cycle Lab Period: The regulation and coordination of the cardiac cycle involves the cardiac conduction system. The pathway of electrical signals originates from the SA (sinoatrial) node located in the right atrium near the entrance of the superior vena cava. The stimulation of the heartbeat and the heart rate originate from the SA node, so it is often called the pacemaker. As the signals pass through the atrial walls toward the AV (atrioventricular) node, contractions of the atria take place. When the AV node has been signaled, the rapid continuation of the electrical signals occurs through the AV bundle (bundle of His), passes through the right and left bundle branches within the interventricular septum, and terminate via the Purkinje fibers throughout the ventricular walls. Once the myocardium has been stimulated, ventricular contractions happen, completing one cardiac cycle. The sympathetic and parasympathetic subdivisions of the autonomic nervous system influence the activity of the pacemaker under various conditions. An increased rate results from sympathetic responses; a decrease rate results from parasympathetic responses. Part 1: Review the sections entitled Cardiac Cycle and Heart Sounds in Chapter 15 of the textbook. Answer the questions below. 1. Put the following letters in order indicating the correct sequence of a cardiac cycle. A, C, D, E, F, G, H: 2. This is the pacemaker of the heart. 3. This is the bundle of His. 4. This branch is on the right side of the interventricular septum. 5. This branch is on the left side of the interventricular septum. 6. This is the interatrial septum. 7. This is the AV node. 8. These are the Purkinje fibers. 9. About % of the blood from the atria passes into the ventricles before the atrial walls contract. 10. The period during which a heart chamber is contracting is called. 11. The period during which a heart chamber is relaxing is called.

2 12. During ventricular contraction, the AV valves (tricuspid and mitral) are. 13. During ventricular relaxation, the AV valves are. 14. The pulmonary and aortic valves open when the pressure in the exceeds the pressure in the pulmonary trunk and aorta. 15. Heart sounds are due to in heart tissues created by changes in blood flow. 16. The first sound of a cardiac cycle occurs when the are closing. 17. The second sound of a cardiac cycle occurs when the are closing. 18. The sound created when blood leaks back through an incompletely closed valve is called a. Part 2: Review the sections entitled Cardiac Conduction System, Electrocardiogram, and Arrhythmias-Clinical Application in Chapter 15 of the textbook. Answer the questions below. 1. The fibers of the cardiac conduction system are specialized tissue. 2. Normally, the node serves as the pacemaker of the heart. 3. The node is located in the inferior portion of the interatrial septum. 4. The large fibers on the distal side of the AV node make up the. 5. The fibers that carry cardiac impulses from the interventricular septum into the myocardium are called. 6. A(n) is a recording of electrical changes occurring in the myocardium during the cardiac cycle. 7. Between cardiac cycles, cardiac muscle fibers remain with no detectable electrical charges. 8. The P wave corresponds to depolarization of the muscle fibers of the. 9. The QRS complex corresponds to the depolarization of the muscle fibers of the. 10. The T wave corresponds to the repolarization of the muscle fibers of the. 11. Why is atrial repolarization not observed in the ECG? 12. A rapid heartbeat is called ; a slow heart beat is called.

3 A number of electrical changes occur in the myocardium as it contracts and relaxes. These changes can be detected by using metal electrodes and an instrument called an electrocardiograph. The recording produced by the instrument is an electrocardiogram, or ECG (EKG). The components of the cardiac cycle is shown in Figure The P-Q interval is often called the P-R interval because the Q wave is often small or absent. The normal P-Q interval is seconds (3-5 boxes on strip). The normal QRS complex duration is less than 0.10 seconds (less than 3 boxes on strip). The ECG can show various problems with the heart. The following shows a normal sinus rhythm that occurs within the heart and is shown on an ECG. Normal Sinus Rhythm Rate is beats per minutes Regular atrial and ventricular rhythm Normal P, QRS, T wave Assessment Questions: Use the ECG strip above to answer the questions. 1. Label one of each: P wave, QRS complex, T wave. 2. How much time passed from the beginning of the P wave to the beginning of the QRS complex? 3. What is the significance of the P-Q (P-R) interval? 4. How can you determine the heart rate from an ECG? (Hint: 25 small boxes = 1 second) 5. What was the heart rate for the normal sinus rhythm ECG? 6. If a person s heart rate is 72 beats per minute, determine the number of QRS complexes that would have appeared on an ECG during the first 30 seconds.

4 7. Evaluate the Arrhythmias on the separate sheet of paper. Listed below are pieces of information for each type of arrhythmia you will encounter on the sheet of paper. Put the correct letter of the arrhythmia next to the name. Ventricular fibrillation (V-fib) No P wave, No P-Q (P-R) interval, No QRS complexes Rhythm is rapid, unorganized, not distinguishable Rate cannot be determined Sinus Bradycardia Normal P-Q interval (3-5 boxes) and QRS complexes (less than 3 boxes) Regular rhythm Beats are slow (less than 60 bpm) Sinus Tachycardia Normal P-Q interval (3-5 boxes) and QRS complexes (less than 3 boxes) Regular rhythm Beats are rapid ( bpm) Atrial Fibrillation Normal P waves are absent replaced by F waves (sawtooth waves) P-Q (P-R) interval is not measurable; QRS complexes look alike and are normal length (less than 3 boxes) Rhythm is irregular with the atrial rate of bpm Atrial Flutter Normal P waves are absent replaced by F waves (sawtooth waves) P-Q (P-R) interval is not measurable; QRS complexes look alike and are normal length (less than 3 boxes) Regular Atrial rhythm (rapid rate: bpm), but Ventricular rhythm is variable Asystole No P waves, No P-Q (P-R) interval, not QRS complexes No rhythm or rate flat line Conclusion Questions: 1. What was the heart rate for the Sinus Bradycardia ECG? bpm 2. What was the heart rate for the Sinus Tachycardia ECG? bpm 3. What is the heart rate for the V-Fib ECG? bpm 4. What is the main difference between atrial fibrillation and atrial flutter?

5 ARRHYTHMIAS A B C

6 ARRHYTHMIAS D E F