IMAT 2018 Q28 [Heart Valves]

Which one of the following statements is correct when the pressure in the ventricles of a
healthy human heart is at its highest?

A. The semi-lunar valves will be closed.
B. The atria of the heart will be filling.
C. A wave of electrical activity will be reaching the atrioventricular node.
D. The heart will be in atrial systole.
E. The atrioventricular valves will be open.

The answer to this question is choice B.

The central concept you have to keep in mind for the question is: “…pressure in the ventricles of a healthy human heart is at its highest”. Thus, you are tasked to check, if the choices are consistent with the scenario given by the central concept to this question.

Let us then rationalize, if the choices are consistent with the time period that the ventricles’ pressure is at the HIGHEST:

  • “The semi-lunar valves will be closed.”: This is NOT consistent with the central concept of this question. The semilunar valves as a reminder, are the pulmonic and aortic valves. It is important to remember, that the pressure difference of the heart chambers on either side of the valve dictates whether a valve will close or open. It would be useful to review this concept, but for this question, recall that if the ventricular pressure is greater than the pressure in front of the valve (which is either the aorta or the pulmonary artery, depending on whether it is related to the left and right ventricle, respectively.), the semilunar valves open. Thus, it is INCORRECT that the semilunar valves will close if the ventricular pressure is at its highest.

  • “The atria of the heart will be filling.”: This is the correct answer. Why? Because of the fact that this is a description of atrial DIASTOLE, which you can recall, happes during ventricular SYSTOLE. (Ventricular systole is the point in the cardiac cycle where the ventricular pressures are at its highest!) Think about it, after ventricular contraction, it needs to be filled with blood again, which is possible if the atria has blood to fill the ventricles in the first place! And the reason the atria is filled with blood is because it has relaxed during atrial diastole. This then makes it the only correct answer out of all the other choices.

  • “A wave of electrical activity will be reaching the atrioventricular node.”: Do NOT be confused by this choice, because it is very important that you use your knowledge of the pathway of the electrical impulse along the cardiac conduction system. As a quick summary, the electrical impulse travels from: SA node → AV node → Bundle of His → Purkinje Fibers, and the electrical impulse reaching the purkinje fibers is the cause of the ventricular contraction. Thus, if you analyze choice C, the electrical impulse is JUST at the AV node, and has NOT YET reached the purkinje fibers! Which means that at this point of the cardiac conduction system, the ventricles are not in contraction YET, which is not consistent with the central concept of this question.

  • “The heart will be in atrial systole.”: This is INCORRECT, if you refer to the rationale of why choice B is correct, this choice is the opposite, which makes it inconsistent with what this question is asking for. Atrial systole does NOT happen at the same time as ventricular systole, which eliminates this from your consideration.

  • “The atrioventricular valves will be open.”: This is NOT consistent with the central concept of this question. The atrioventricular valves as a reminder, are the mitral and tricuspid valves. Again, please remember that the pressure difference of the heart chambers on either side of the valve dictates whether a valve will close or open. For this question, recall that if the ventricular pressure is greater than the atrial pressure, the atrioventricular valves CLOSE. Thus, it is INCORRECT that the atrioventricular valves will open if the ventricular pressure is at its highest.