Snapshot A medical student is shadowing a cardiologist for the day. In clinic, a 60-year-old man presents for follow-up after having a myocardial infarction 1 month ago. His comorbidities include type 2 diabetes mellitus, rheumatoid arthritis, and hypertension. The cardiologist explains that because of the myocardial infarction, he has likely lost some amount of myocardium. Therefore, this patient’s Starling Curve is changed from baseline. (Negative inotropy) Introduction The Frank-Starling relationship based on length-tension relationship in the ventricles ↑ tension ∝ ↑ length ↑ contractility ∝ ↑ end-diastolic volume (EDV) (increased blood volume stretches the cardiac muscle fibers) EDV = preload this holds true until very high levels of EDV ventricles reach their limit and cannot accommodate the high levels of venous return Contractility (inotropy) intrinsic ability of myocardial cells to develop force Positive inotropy e.g., digoxin and ↑ catecholamines increase in stroke volume and cardiac output for a specific EDV Negative inotropy e.g., myocardial infarction (loss of myocardium), β-blockers, Ca2+ channel blockers, dilated cardiomyopathy, and congestive heart failure a decrease in stroke volume and cardiac output for a specific EDV
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