Chapter 4: Measurements of Cardiac Function

Question 1

Explain how you can use the PV loop to assess cardiac contractility?

Answer 1

can assess the PV curve/line relationship at the end of systole (end-systolic left ventricular pressure-volume relationship)–> will be steeper with increased contractility and flatter with decreased contractility

Question 2

List the equation to calculate cardiac output using the Fick principle.
What samples need to be obtained to facilitate this?

Answer 2

Q = (inhaled O2 - exhaled O2) / (arterial O2 - central venous mixed O2)

need arterial blood sample and mixed venous sample (from PA)

need to intubate patient to measure inspired and expired O2 volumes

Question 3

What is the cardiac index?

Answer 3

cardiac output over the body surface area

Question 4

What side of the intervertebral septum does ventricular depolarization typically start?

Answer 4

left side

Question 5

Define the mean electrical axis

Answer 5

the average direction of the cardiac electric current during the R wave

Find the lead with the tallest R wave –> can find direction on Einthoven triangle polarity chart (e.g., lead 2 60 degree) –> should be between 0 and 90 degrees

deviations can indicate physical shifting of the heart or concentric hypertrophies

Question 6

What is a normal range for the mean electrical axis?

Answer 6

0-90 degrees (i.e., lower left-hand quadrant)

Question 7

What does a left-axis or right-axis deviation of the mean electrical axis indicate?

Answer 7

either left of right shifting of the heart or left- or right-sided ventricular concentric hypertrophy

Question 8

What are the 3 additional unipolar limb leads called and what limb do they each refer to?

Answer 8

aVF - left leg lead
aVR - right arm lead
aVL- left arm lead

Question 9

The lowest ECG amplitude of the R wave will be read on the lead that is XXXXXX to the lead of the mean electrical axis

Answer 9

perpendicular