CVS 113 Syncope

Question 1

What is the definition of syncope?

Answer 1

transient loss of consciousness due to inadequate perfusion of the brain

Question 2

Describe a vasovagal attack

Answer 2

Peripheral dilatation results in venous blood pooling with subsequent decreased return to the heart
Increased force of cardiac contractions stimulates mechanoreceptors and decreased ventricular stretch –> to the CNS = bradycardia, further vasodilatation, decreased BP and faint

Question 3

Describe postural hypotension

Answer 3

Systolic drop of 20mmHg or more upon standing
reflex vasoconstrictive mechanisms absent
worse with dehydration, diuretics and some vasodilators

Question 4

What are stokes-adams attacks?

Answer 4

sudden loss of consciousness unrelated to posture
- high grade AV block = intense bradycardia and still ventricles
= sudden collapse

Question 5

What controls blood pressure in the short term?

Answer 5

baroreceptor reflex

Question 6

Where are the baroreceptors found?

Answer 6

atrium, left ventricle, coronary arteries, arch of aorta, carotid sinuses

Question 7

If there is increased arterial pressure how does the baroreceptor reflex respond?

Answer 7

increased arterial pressure = increased impulse firing from baroreceptor stimulation = medullary stimulation = increased PSS activity via vagus nerve –> acts on SAN to decrease HR

Question 8

What are the 3 long term mechanisms to control blood pressure?

Answer 8

Osmoregulation, pressure natriuresis and the renin-angiotensin- aldosterone system

Question 9

What do the hypothalamic osmoreceptors sense?

Answer 9

Na+ in ECF

Question 10

Where is renin released from?

Answer 10

the juxtoglomerular apparatus

Question 11

What is the action of renin?

Answer 11

cleaves angiotensinogen to angiotensin 1

Question 12

Where is angiontensin 1 converted to angiotensin 2 and by what?

Answer 12

angiotensin converting enzyme in the lung

Question 13

What are the actions of angiotensin 2?

Answer 13

vasoconstriction, Na+ reabsorption in the PCT, increase thirst, ADH release and aldosterone release

Question 14

Where is aldosterone released from?

Answer 14

the adrenal cortex

Question 15

What does aldosterone cause>

Answer 15

Na+ reabsorption in the DCT

Question 16

What is the resting cardiac membrane potential?

Answer 16

-90mV

Question 17

Describe the process that occurs in a cardiac muscle action potential after depolarisation?

Answer 17

Depolarisation triggers Na+ influx into the cell = further Na+ channel opening = rapid depolarisation
Calcium channels open more slowly = plateau phase
Voltage gated calcium channels open on sarcoplasmic reticulum = contraction
K+ channels open and and calcium slowly flows out of channels also = reporlarisation

Question 18

Describe the conducting pathway of the heart

Answer 18

SAN –> AP transmitted cell to cell in atria via low resistant gap junctions = coordinated cell contraction –> AVN in atrial septum –> slow causing delay allows ventricles to fill –> Bundle of His –> R/L bundle branch –> ventricular muscle

Question 19

What is first degree AV block?

Answer 19

Delay at the AVN/Bundle of His
Normal, degenerative disease or toxicitiy
Prolonged PR interval

Question 20

Describe Type 1 mobitz second degree AV block

Answer 20

Progressively longer PR interval until a beat is dropped

Question 21

Describe Type 2 mobitz second degree AV block

Answer 21

Normal PR intervals with occasional dropped beats.
QRS intervals dropped at random
Signifies serious heart disease

Question 22

Describe third degree AV block?

Answer 22

Atrioventricular dissociation
Complete heart block where no atrial impulses make it through the ventricles
Atria beat normal rate but ventricles generate escape rhythm - wide QRS complex