TEST BANK FOR PORTH’S PATHOPHYSIOLOGY 10TH EDITION BY NORRIS CHAPTER 28: Disorders of Cardiac Conduction and Rhythm

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1. A physician has ordered the measurement of a cardiac patient's electrolyte levels as part of the client's morning blood work. Which of the following statements best captures the importance of potas... sium in the normal electrical function of the patient's heart? A) Potassium catalyzes the metabolism of ATP, producing the gradient that results in electrical stimulation. B) Potassium is central to establishing and maintaining the resting membrane potential of cardiac muscle cells. C) The impermeability of cardiac cell membranes to potassium allows for action potentials achieved by the flow of sodium ions. D) The reciprocal movement of one potassium ion for one sodium ion across the cell membrane results in the production of an action potential. Ans: B Feedback: The selective permeability of cell membranes to potassium, and its near-impermeability to sodium ions, produces the resting membrane potential of cardiac cells. Potassium does not catalyze the metabolism of ATP, and sodium and potassium ions do not move across the cell membrane in a 1:1 ratio. 2. Which of the following statements describes phase 4 of the action potential of cells in the sinoatrial (SA) node? A) A slow depolarization occurs when Na+ is transported out of the cell and K+ moves back in, resulting in resting membrane potential. B) The cells are capable of responding to a greater than normal stimulus before the resting membrane potential is reached. C) The fast sodium channels in the cellular membranes close, causing an abrupt decrease in intracellular positivity. D) Potassium permeability is allowing the cell membrane to remain depolarized, and Ca2+ channel opens moving Ca2+ back into the cell. Ans: A Feedback: During phase 4 in the cells of the SA node, a slow leakage of current through the slow channels of the cellular membrane leads to spontaneous depolarization; this slow response enables pacemaker function. Answer B describes the relative refractory period of the action potential curve, which occurs at the end of phase 3 in cardiac cells, and answer C describes phase 1 of the action potential, which signals the end of depolarization. The sodium–potassium pump transports sodium out of the cell and a smaller amount of potassium into it, contributing to the negative intracellular charge of the resting membrane potential in phase 4. 3. An ECG technician is placing leads on a patient who has presented to the emergency department with a sudden onset of chest pain. The technician would recognize which of the following facts about the placement of leads and the achievement of a clinically accurate ECG? A) The electrical potential recorded by a lead on an extremity will vary significantly depending on where the lead is placed on the extremity. B) The chest leads measure electrical activity on the horizontal plane, while limb leads measure it on the vertical plane. C) Limb leads measure the electrical activity of the heart indirectly through the activity of adjacent skeletal muscle. D) A total of 12 chest leads are necessary to attain the most accurate ECG. Ans: B Feedback: A complete ECG is obtained by combining data from chest leads, which measure activity on the horizontal plane, and limb leads, corresponding to the vertical or frontal plane. The electrical potential recorded by a lead on an extremity should not vary significantly depending on where the lead is placed on the extremity, and limb leads do not measure electrical activity by way of skeletal muscle activity. A total of 12 leads, only six of which are on the chest, are necessary for a complete ECG. [Show More]

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