Which of the following is a TRUE statement regarding determinants of myocardial oxygen demand?
**Core Concept**
Myocardial oxygen demand is determined by several factors that influence the heart's workload, including contractility, heart rate, preload, and afterload. These determinants can be modulated by various physiological and pharmacological interventions to optimize cardiac function.
**Why the Correct Answer is Right**
The correct answer is related to the Frank-Starling mechanism, which describes the relationship between the end-diastolic volume (preload) and the stroke volume of the heart. According to this mechanism, an increase in preload leads to an increase in stroke volume, as the heart muscle stretches and contracts more forcefully. This is because the Frank-Starling mechanism is based on the principle of length-tension relationships in cardiac muscle fibers, where increased muscle length leads to increased force of contraction.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because heart rate (rate-pressure product) is a determinant of myocardial oxygen demand, but it is not the correct answer in this context.
**Option B:** This option is incorrect because afterload is a determinant of myocardial oxygen demand, but it is not the correct answer in this context.
**Option C:** This option is incorrect because contractility is a determinant of myocardial oxygen demand, but it is not the correct answer in this context.
**Clinical Pearl / High-Yield Fact**
The Frank-Starling mechanism is a critical determinant of myocardial oxygen demand and is affected by changes in preload, which can be modulated by interventions such as fluid administration or vasodilation.
**Correct Answer:** C.