A 54-year-old man is admitted to the hospital due to cough, shortness of breath, and chest discomfort. He has a known history of coronary artery disease and underwent coronary artery bypass graft surgery 3 years ago. As a result of drug therapy, the left ventricular pressure-volume loop changes from a solid to a dashed line, as shown in the graph below (the loop is unchanged in areas where no dashed line is seen): Which of the following parameters is most likely increased as a result of this change?

Question

A 54-year-old man is admitted to the hospital due to cough, shortness of breath, and chest discomfort.  He has a known history of coronary artery disease and underwent coronary artery bypass graft surgery 3 years ago.  As a result of drug therapy, the left ventricular pressure-volume loop changes from a solid to a dashed line, as shown in the graph below (the loop is unchanged in areas where no dashed line is seen):  Which of the following parameters is most likely increased as a result of this change?

Quizplus · Accepted Answer

11ec160b_3c8b_34d9_9249_b17e11d7e4b7_MD0001_00 As a result of drug therapy, point 3 on this patient's left ventricular (LV) pressure-volume loop shifts up and to the left; this represents an increase in cardiac contractility that would occur with a positive inotropic agent (eg, digoxin, dobutamine). Although LV preload, represented by the volume at point 1, is unchanged (Choice E), the increase in contractility causes an increase in the fraction of LV volume ejected (ie, increased ejection fraction) and increases stroke volume (the horizontal distance between points 1 and 3). The volume remaining in the left ventricle at the end of systole (end-systolic volume represented by the volume at point 3) is consequently decreased (Choice B). LV afterload (the maximum pressure reached during blood ejection) is slightly increased due to the increase in contractility. (Choices A and D) LV end-diastolic pressure (indicated at point 1) and compliance are unchanged in this patient. Compliance is represented by the curve at the bottom of the pressure-volume loop (between point 4 and point 1) and determines the rate of LV pressure increase as LV volume increases during diastolic filling. Compliance is typically unchanged in the short term, but it can change over the long term. Decreased LV compliance (eg, due to concentric LV hypertrophy from prolonged systemic hypertension) would increase the slope of the compliance curve and increase end-diastolic pressure for a given LV end-diastolic volume. Educational objective: An increase in cardiac contractility shifts the top left corner (point 3) of the left ventricular pressure-volume loop up and to the left and increases stroke volume due to an increase in the fraction of LV preload that is ejected during systole (ie, increased ejection fraction).

A 54-Year-Old Man Is Admitted to the Hospital Due to Cough