Critical Care Ch11

ANS: A, C, E Stroke volume (SV) as a value is influenced by three primary factors: preload, afterload, and contractility. Cardiac output (CO) is determined by SV HR = CO. Preload is the volume of blood in the left ventricle at the end of diastole.

1. Which factors influence stroke volume? (Select all that apply.) a. Afterload b. Cardiac output c. Contractility d. Heart rate e. Preload

ANS: C With an intrinsic rate of 60 to 100 beats/min, the sinoatrial node is the primary pacemaker in a healthy heart. The atrioventricular node beats 40 to 60 beats/min. Ventricular tissue must have an electrical impulse to contract. Purkinje fibers beat 15 to 40 beats/min.

1. Which structure is the primary or natural pacemaker of the heart? a. Ventricular tissue b. Atrioventricular node c. Sinoatrial node d. Purkinje fibers

ANS: D The thebesian vessels return blood to the left ventricle. The mixing of unoxygenated blood with freshly oxygenated blood is called a physiologic shunt. A ventricular septal defect (VSD) allows mixing of blood from both ventricles. The clinical impact depends on the size of the intracardiac shunt. A VSD is a congenital opening between the ventricles; a ventricular septal rupture can occur as a complication of a large anterior wall myocardial infarction.

10. Which is an example of a physiologic shunt? a. A ventricular septal defect b. Blood returning from the inferior vena cava to the right atrium c. A septal infarct d. The thebesian vessels returning deoxygenated blood to the left ventricle

ANS: C The adventitia is the outermost layer of the artery that helps strengthen and shape the vessel. The media is the middle layer that is made up of smooth muscle and elastic tissue. The intima is the innermost layer consists of a thin lining of endothelium and a small amount of elastic tissue.

11. What is the name of outermost layer of an artery? a. Tunica b. Intima c. Adventitia d. Media

ANS: D The diameter of a capillary is less than that of an arteriole, but the pressure is relatively low as a result of the large cross-sectional area of the branching capillary bed.

12. Which of the following is most descriptive of the capillary? a. Large diameter, low pressure b. Small diameter, high pressure c. Large diameter, high pressure d. Small diameter, low pressure

ANS: B The cardiac muscle is a functional syncytium in which depolarization started in any cardiac cell is quickly spread to all of the heart.

13. Depolarization of one myocardial cell will likely result in what physiologic response? a. Completion of the action potential in that cell before a new cell can accept an impulse b. Quick depolarization and spread to all of the heart c. Depolarization of only cells superior to the initial depolarization d. Quick depolarization of only cells inferior to the initial depolarization

ANS: D In a myocardial cell, the normal resting membrane potential is -80 to -90 mV.

14. What is the normal resting membrane potential of a myocardial cell? a. 10 to 20 mV b. 30 to 40 mV c. -20 to -30 mV d. -80 to -90 mV

ANS: C The final repolarization phase is phase 3 of the action potential. Phases 1 and 2 (partial repolarization) occur as the AP slope returns toward zero. The plateau that follows is described as phase 2. In phase 4 the AP returns to an RMP of -80 to -90 mV.

15. Which phase is the final repolarization phase of the action potential? a. Phase 1 b. Phase 2 c. Phase 3 d. Phase 4

ANS: D The parasympathetic nervous system and the sympathetic nervous system operate to create a balance between relaxation and fight-or-flight readiness. They affect cardiovascular function by slowing the heart rate during periods of calm and increasing it in response to sympathetic stimulation.

16. Which statement regarding the autonomic nervous system's role in the regulation of heart rate is true? a. Parasympathetic influences increase heart rate. b. Sympathetic influences are predominantly present. c. Parasympathetic influences are only compensatory. d. Both sympathetic and parasympathetic influences are normally active.

ANS: A The right coronary artery provides the blood supply to the sinoatrial and atrioventricular (AV) nodes in more than half the population. The left coronary artery is a short but important artery that divides into two large arteries, the left anterior descending and the circumflex arteries. These vessels serve the left atrium and most of the left ventricle. The term dominant coronary artery is used to describe the artery that supplies the posterior part of the heart.

17. A patient is admitted with a diagnosis of acute myocardial infarction. The monitor pattern reveals bradycardia. Occlusion of which coronary artery most likely resulted in bradycardia from sinoatrial node ischemia? a. Right b. Left anterior descending c. Circumflex d. Dominant

ANS: A Ejection fraction is expressed as a percent, with normal being at least greater than 50%. An ejection fraction of less than 35% indicates poor ventricular function (as in cardiomyopathy), poor ventricular filling, obstruction to outflow (as in some valve stenosis conditions), or a combination of these.

18. An echocardiogram reveals an ejection fraction of 55%. On the basis of this information, how would the patient's cardiac function be described? a. Adequate b. Mildly decreased c. Moderately decreased d. Severely decreased

ANS: B Cardiac output is normally expressed in liters per minute (L/min). The normal cardiac output in the human adult is approximately 4 to 8 L/min. It is approximately 4 to 6 L/min at rest and increases with exercise.

19. Which of the following values reflects a normal cardiac output at rest? a. 2.5 L/min b. 5.8 L/min c. 7.3 L/min d. 9.6 L/min

ANS: B The atrioventricular (AV) node delays the conduction impulse from the atria (0.8-1.2 seconds) to provide time for the ventricles to fill during diastole.

2. The atrioventricular (AV) node delays the conduction impulse from the atria (0.8-1.2 seconds) for what reasons? a. To limit the amount of blood that fills the ventricle from the atria b. To provide time for the ventricles to fill during diastole c. To limit the number of signals the ventricles receive in some rhythms d. To allow the atria to rest between signals

ANS: C Whereas a patient with hypovolemia has too little preload, a patient with heart failure has too much preload.

20. A patient is admitted with right- and left-sided heart failure. The nurse's assessment reveals that the patient has 3+ pitting edema on the sacrum, blood pressure of 176/98 mm Hg, and bilateral crackles in the lungs. The patient is experiencing shortness of breath and chest discomfort. On the basis of this information, how would the nurse evaluate the patient's preload status? a. The patient is hypovolemic and has too little preload. b. The patient is experiencing congestive heart failure (CHF) and has too little preload. c. The patient is experiencing heart failure and has too much preload. d. The patient is hypertensive and the preload is not a factor.

ANS: A Therapeutic management to decrease afterload is aimed at decreasing the work of the heart with the use of vasodilators. Placing the patient in high Fowler position will cause an increase in the workload of the heart. Elevation of the extremities will ease the venous return back to the heart. Increasing IV fluids will cause an increased workload on the heart.

21. A patient is admitted with right- and left-sided heart failure. The nurse's assessment reveals that the patient has 3+ pitting edema on the sacrum, blood pressure of 176/98 mm Hg, and bilateral crackles in the lungs. The patient is experiencing shortness of breath and chest discomfort. Increased afterload is probably present related to the patient's blood pressure. Which therapeutic measure will most likely decrease afterload in this patient? a. Administration of vasodilators b. Placement in high Fowler position c. Elevation of extremities d. Increasing intravenous fluids

ANS: B Actin and myosin form cross-bridges, allowing myocardial contraction to take place. Z-disk, A-band, I-band, and M-band are all portions of the sarcomere functional unit to promote contraction in the heart. Renin converts the protein angiotensinogen to angiotensin I. When angiotensin I passes through the pulmonary vascular bed, it is activated by angiotensin-converting enzyme to become angiotensin II.

22. What are the two important proteins contained within the cardiac cells that contribute to contraction? a. Z-disk and A-band b. Actin and myosin c. I-band and M-band d. Renin and angiotensin

ANS: D The pulmonic valve allows blood flow into the pulmonary artery, and the aortic valve allows blood flow into the aorta. The tricuspid (right) and mitral valves (left) are located between the atria and the ventricles.

23. What is the name of the valve that allows blood flow into pulmonary artery? a. Aortic b. Tricuspid c. Mitral valve d. Pulmonic valves

ANS: A The three main areas of impulse propagation and conduction are (1) the sinoatrial node, (2) the atrioventricular node, and (3) the conduction fibers within the ventricle, specifically the bundle of His, the bundle branches, and the Purkinje fibers. Interruption or malfunction of any part of the conduction pathway can result in dysrhythmias specific to that structure.

24. Place the following components of the cardiac conduction pathway in the correct anatomic order. 1. Atrioventricular node 2. Bundle branches 3. Bundle of His 4. Internodal pathways 5. Purkinje fibers 6. Sinoatrial node a. 6, 1, 4, 3, 2, 5 b. 6, 1, 3, 2, 4, 5 c. 6, 1, 4, 2, 3, 5 d. 4, 3, 2, 5, 6, 1

ANS: D The coronary arteries are perfused during diastole. When the heart rate increases, the diastolic time decreases as each contraction has less time to be completed. This decreases the time the coronary arteries have to deliver oxygenated blood to the myocardium. The symptoms described are caused by a lack of oxygen in the myocardium.

3. Why do many patients with very high heart rates frequently have chest pain and shortness of breath? a. Patients with heart disease frequently have an anxiety disorder as well. b. The rapid pounding of the heart in the chest wall causes the physical pain. c. The heart muscle gets tired from the increased work. d. The decreased diastolic time decreases oxygen delivery to the myocardium.

ANS: B Poor skin turgor could suggest dehydration. Dehydration can cause orthostatic hypotension because of low capacitance reserves from hypovolemia. Supine blood pressure of 146/93 mm Hg would be considered hypertensive, and the patient would most likely experience a headache rather than dizziness. A resting heart rate of 96 beats/min is still considered a normal value.

4. A patient reports feeling dizzy after standing quickly. Which finding could provide a clue regarding the cause? a. Hemoglobin level of 14.0 g/dL and hematocrit level of 42.3% b. Poor skin turgor with extended tenting c. Supine blood pressure of 146/93 mm Hg d. Resting heart rate of 96 beats/min

ANS: A Calcium channel-blocking drugs, such as verapamil and diltiazem, inhibit the inward Ca++ current into pacemaker tissue, especially the atrioventricular (AV) node. For this reason, they are used therapeutically to slow the rate of atrial tachydysrhythmias and protect the ventricle from excessive atrial impulses.

5. A patient presents with atrial fibrillation, a heart rate of 156 beats/min, and a blood pressure of 124/76 mm Hg. The practitioner orders diltiazem, a calcium channel blocker, to be given slowly by intravenous push. Why did the practitioner choose this medication to treat this patient's atrial tachyarrhythmia? a. Diltiazem decreases the calcium influx into the atrioventricular (AV) nodal tissue and decreases the speed of impulse conduction. b. Diltiazem increases the calcium influx into the AV nodal tissue and decreases the speed of impulse conduction. c. Diltiazem decreases the calcium influx into the myocardial tissue and decreases the strength of heart contraction. d. Diltiazem increases the calcium influx into the myocardial tissue and decreases the strength of heart contraction.

ANS: B If the fluid collection in the sac (pericardial effusion) impinges on ventricular filling, ventricular ejection, or coronary artery perfusion, a clinical emergency may exist that necessitates removal of the excess pericardial fluid to restore normal cardiac function. Myocardial ischemia is damage of the myocardium muscle as the result of a heart attack.

6. What is one hemodynamic effect of a pericardial effusion? a. Increased ventricular ejection b. Decreased ventricular filling c. Myocardial ischemia d. Increased afterload

ANS: B Atrial contraction, also known as "atrial kick," contributes approximately 20% of blood flow to ventricular filling; the other 80% occurs passively during diastole.

7. What percentage of volume does atrial kick contribute to ventricular filling? a. 10% b. 20% c. 5% d. 45%

ANS: A The atrioventricular (AV) valves are open during ventricular diastole (filling) and prevent backflow of blood into the atria during ventricular systole (contraction). Semilunar valves prevent the backflow of pulmonic and aortic blood back into the ventricles

8. What is the function of the atrioventricular (AV) valves? a. Prevent backflow of blood into the atria during ventricular contraction b. Prevent blood regurgitation back into the ventricles c. Assist with blood flow to the lungs and aorta d. Contribute to ventricular filling by atrial kick

ANS: B The conduction delay at the atrioventricular (AV) node allows adequate time for ventricular filling from atrial contraction.

9. Which step of impulse conduction is most conducive to atrial kick? a. The firing of the sinoatrial node, which results in atrial depolarization b. The conduction delay at the atrioventricular (AV) node, allowing time for filling c. Conduction through the bundle of His, enhancing ventricular depolarization d. Conduction to the Purkinje fibers, allowing for ventricular contraction