CVS 113 Syncope Flashcards
What is the definition of syncope?
transient loss of consciousness due to inadequate perfusion of the brain
Describe a vasovagal attack
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
Describe postural hypotension
Systolic drop of 20mmHg or more upon standing
reflex vasoconstrictive mechanisms absent
worse with dehydration, diuretics and some vasodilators
What are stokes-adams attacks?
sudden loss of consciousness unrelated to posture
- high grade AV block = intense bradycardia and still ventricles
= sudden collapse
What controls blood pressure in the short term?
baroreceptor reflex
Where are the baroreceptors found?
atrium, left ventricle, coronary arteries, arch of aorta, carotid sinuses
If there is increased arterial pressure how does the baroreceptor reflex respond?
increased arterial pressure = increased impulse firing from baroreceptor stimulation = medullary stimulation = increased PSS activity via vagus nerve –> acts on SAN to decrease HR
What are the 3 long term mechanisms to control blood pressure?
Osmoregulation, pressure natriuresis and the renin-angiotensin- aldosterone system
What do the hypothalamic osmoreceptors sense?
Na+ in ECF
Where is renin released from?
the juxtoglomerular apparatus
What is the action of renin?
cleaves angiotensinogen to angiotensin 1
Where is angiontensin 1 converted to angiotensin 2 and by what?
angiotensin converting enzyme in the lung
What are the actions of angiotensin 2?
vasoconstriction, Na+ reabsorption in the PCT, increase thirst, ADH release and aldosterone release
Where is aldosterone released from?
the adrenal cortex
What does aldosterone cause>
Na+ reabsorption in the DCT
What is the resting cardiac membrane potential?
-90mV
Describe the process that occurs in a cardiac muscle action potential after depolarisation?
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
Describe the conducting pathway of the heart
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
What is first degree AV block?
Delay at the AVN/Bundle of His
Normal, degenerative disease or toxicitiy
Prolonged PR interval
Describe Type 1 mobitz second degree AV block
Progressively longer PR interval until a beat is dropped
Describe Type 2 mobitz second degree AV block
Normal PR intervals with occasional dropped beats.
QRS intervals dropped at random
Signifies serious heart disease
Describe third degree AV block?
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
