Cardiology Flashcards
What is the potential energy?
Additional work that could be accomplished by contraction if ventricle would empty completely
What is preload?
Degree if tension on muscle when it begins to contract
Usually considered end diastolic pressure
What is afterload?
Load the muscle has to work against
Pressure in the aorta for Lv
Tension time index
Oxygen consumption = tension in heart muscle with contraction by duration of time
Heart efficiency
Ration of work output to total chemical energy expenditure
Frank Starling mechanism
The greater the stretching of heart muscle during filling, the great the force of contraction
Calculate stroke volume
End diastolic volume - end systolic volume
Calculate cardiac output
Stroke volume X HR
What are possible causes of long QT syndromes
Congenital (mutations if Na or K channel genes)
Hypomagnesemia
Hypokalemia
Hypocalcemia
Drugs: quinidine, fluorquinolones, erythromycin
Lidocaine
Depresses increase in Na permeability during AP, Blocks rhythmical discharge of focal point of abnormal rhythm
What are reasons for impulse re-entry(circus movement)
Can cause ventricular fibrillation
Overall happens when impulse come to already stimulated muscle that is not refractory any more
- pathway around circle is longer (dilated heart)
- velocity of conduction is decreased (purkinje system blockage, ischemia, hyperkalemia)
- shortened refractory period (drugs- epi)
Digitalis
Cardiotonic drug
Increases Ca in cardiac muscle cells by inhibition of Na/K ATPase
—> increase of intracellular Na and slowing of Na/Ca exchange pump = more Ca in cardiomyocytes
also has some parasympathetic effects, especially on atria - can decrease HR and be used for atrial arrhythmia ( afib and flutter )
Atrial natiuretic peptide
Released by atrial walls when stretched
- heart failure increases right and left atrial pressures
Direct effect on kidney to excrete water and Na - prevent extreme congestive symptoms
Tetralogy of fallot
VSD
Overriding aorta
Right ventricular outflow obstruction
Right ventricular hypertrophy
Eisenmenger‘s Syndrome
When initial left-right shunt reversed to right- left due to progressive increase in pulmonary hypertension - pulmonary vascular resistance increases and if pulmonary vascular pressure is high enough reversal happens
More common in cattle
Which breeds are predisposed for VSD?
Bovine: Hereford, Limousine
Equine: Arabians, SB, QH
NT - proBNP
From, stimulated by, functions
From ventricular and atrial myocytes
Due to volume overload / stretching
Functions:
Decrease vagal tone
Decrease renin and aldosterone
Decrease venous and arterial tone
Decrease vascular proliferation
Decrease cardiac fibrosis and proliferation
Increase GFR and decrease Na absorption
Non cardiac reasons: hyperthyroidism, systemic hypertension, pulmonary hypertension, renal insufficiency
Urotensin II
Endogenous cardiostimulatory peptide
Potent vasoconstriction
Potent positive inotropy
May pay role in cardiac hypertrophy
Not yet used in vetmed
Neuropeptide Y
Released with NE from sympathetic endings
Influence in coronary vasoconstriction
Myocardial contraction
Mitogenic and hypertrophic effects on vascular smooth muscle and cardiomyocytes
Increase in heart failure
Not yet used in vetmed
Endothelin
Potent vasoconstrictor
ET-1 produced in heart failure
- increase contractility, vasoconstriction, cardiac fibroblast activation, worsening of hypertrophy
High in pre clinical and overt heart failure
Epinephrine and norepinephrine
- Function and receptors
Epinephrine:
- b1 - myocytes, increased contractility
- b2- vasculature, vasodilation
Norepinephrine
b1 - myocytes, increased contractility
a1 - vasculature, vasoconstriction
Effects of angiotensin
- vasoconstriction
- increased sympathetic tone (central, ganglionic and presynaptic NE release and decrease of presynaptic NE uptake)
- aldosterone secretion
- fluid and Na retention
- increased cardiac hypertrophy and fibrosis
ADH
produced in supraotpic nuclei in hypothalamus
saved and secreted by neurohypophysis
secretion stimulated by:
osmoreceptors in hypothalamus and ATII
AV1 receptors - vasconstriction
AV2 receptors - distal collecting ducts
ANP
Mechanism, Stimulated by, effects
atrial natriuretic peptide
from atrium, reacts to stretching of myocytes = increased preload
- stimulates vasodilation (via cGMP)
- stimulates diuresis by kidneys
- inhibits aldosteron secretion