Chapter 5: Cardiac Abnormalities

Question 1

List 2 differentials for supraventricular tachycardia and explain their mechanisms

Answer 1

Ectopic impulse - myocardial cells (usally atrial) that’s not the SA ndoe usually from structural damage or hypoxia sends impulses at a higher rate than SA node HR –> overrides SA node

Reentry - impulses should die off within the atria after passing through AV node. If there is a pathologic reentry circuit, impulse won’t die off and circle back repeatedly, also stimulating a higher ventricular rate on the way

Question 2

Explain the compensatory pause (why does it occur) as well as the postextrasystolic potentiation.

Answer 2

compensatory pause: missed beat due ventricular cells still being refractory when next SA impulse comes

postextrasystolic potentiation: due to the compensatory pause the ventricles had more time to fill –> increased SV

Question 3

What is the normal length of a QT interval? Under what condition does this reference not apply

Answer 3

40% or less of the R-R interval lenght

> 50% considered prolonged

Question 4

What electrolyte disorders can cause a prolonged QT interval?

Answer 4

hypokalemia
hypocalcemia
hypomagnesemia

Question 5

What are patients with QT interval prolongation predisposed to and why?

Answer 5

torsades de pointes
prolongs action potential and extension of the vulnerable period of the myocytes to be excessively stimulated

Question 6

Explain how a stenotic versus a insufficient cardiac valve differ in the way they will cause remodelling of the heart

Answer 6

stenotic valve –> preceding chamber has to build up more pressure to create forward flow –> increased pressure within that chamber

high pressure –> concenric hypertrophy (i.e., thick muscles

insufficient valve –> backflow into preceeding chamber –> volume large

high volume –> eccentric hypertrophy (i.e., dilation)

Question 7

How does aortic stenosis change the Wigger’s diagram?

Answer 7

high LV pressure required for forward flow –> LV pressure will be above aortic pressure

aortic pressure rises more slowly than normal and has a lower systolic pressure

Lower pulse pressure (because SAP lower)

Question 8

What type of murmur will you hear with aortic stenosis

Answer 8

systolic

Question 9

How does aortic stenosis change the heart chamber size, how does this change the mean electrical axis?

Answer 9

LV hypertrophy –> causes left deviation of the mean electrical axis, i.e., left upper corner

Question 10

How does mital stenosis affect the wigger’s diagram and what type of murmur will you hear?

Answer 10

increased LA pressure during diastole and systole

diastolic murmur

Question 11

How does aortic insufficiency change the wigger’s diagram and what type of murmur do you hear?

Answer 11

backflow of blood into LV during diastole –>

diastolic aortic pressure falls steeper (Faster and further than normal)

diastolic murmur

will have a large pulse pressure

Question 12

How does mitral regurgitation affect the wigger’s diagram and what type of murmur do you hear?

Answer 12

backflow of blood into LA during systole –> higher LA pressure during systole

systolic murmur

Question 13

How does third degree AV block affect the RA or jugular pressure tracings?

Answer 13

atria and ventricle contract uncoordinated –> atria will contract against a closed AV valve –> large a wave –> “cannon wave”