CHF & cardiac remodelling Flashcards
Furosemide MOA
inhibit sodium and chloride reabsorption by competing with Cl for the Na/K/Cl symporter in the ascending limb of the loop of Henle (decrease in intracellular Na, K, Cl)
- also inhibits absorption of sodium and chloride in the proximal & distal tubules)
- increases excretion of calcium, Mg, bicarb, ammonium, phosphate
Frank-Starling curve
SV vs LVEDV/P
curve depends on contractility
increase in LVEDP = increase in SV, to some extent
HF: increase LVEDP in order to increase SV
Ejection fraction
EF = SV/end-diastolic volume
usually 50-75%
Pressure-volume loops for cardiac cycle
a = mitral valve opens (atrial P > ventricular P)
a-b =diastolic filling (slope dependent on compliance)
b = mitral closes
b-c = isovolumetric contraction
c = aortic valve opens
c-d: systolic ejection (vol decreases, but P rises until ventricular relaxation occurs) - pressure at this point = afterload
d = aortic valve closes
d-a = isovolumetric relaxation
b-a = SV
Effect of preload on P-V curve
Increase in preload = increase in SV (longer a-b, but also higher slope as pressure increases)
Effect of afterload on P-V curve
Increase in afterload = longer isovolumetic contraction (need to reach higher P before ejection)
- lower SV, higher ESV
Relationship between afterload and ESV mostly linear (ESPVR)
Effect of contractility on P-V curve
Slope of ESPVR line
Increased contractility - increased slope
Increase in contractility –> higher SV, lower ESV
Compensatory response to low CO
Raise HR (reflex tachycardia) Neurohormonal activation via RAAS and SNS Ventricular remodelling (concentric for higher pressure, eccentric for higher volume)
Cardiac hypertrophy incidence
15% of popn
50% popn with moderate HTN
90% popn with CV disease
Concentric hypertrophy
more relative wall thickness results from P overload increased LV mass increased contractility increased LVEDV (only when dilated) Length increases by 5% X-sectional area increases by 150%
Eccentric hypertrophy
Less relative wall thickness Results from V overload Increased LV mass Decreased contractility Increased LVEDV (when dilated) Length increased by 30% X-sectional area increased by 50%
Qualitative compensation due to increased myocardial workload
Decrease amount of work by SR Ca ATPase Increase contractile proteins Increase glycolysis, decrease FA oxidation Increase cardiac epi/nepi receptors increasing ANP/BNP expression
Pathological hypertrophy
No long term benefit Interstitial fibrosis Fetal gene expression increase Decreased cardiac function over time Associated with heart failure Not reversible, unless HTN treated cardiac work drops significantly after ischemia
Heart failure definition
Inability of the heart to pump blood at sufficient rate (low CO) to meet metabolic demands of the body, or to do so at abnormally high filling pressures, or both.
Mechanisms of heart failure
Low preload
High afterload
Reduced contractility
Neurohormonal
Neural response to low CO
Decreased baroreceptor firing –> increased SNS and decreased PNS
o Increased HR via beta-1 receptors
o Increased ventricular contractility
o Arterial/venous vasoconstriction via alpha receptors (NB, this increases VR too)
o Increase renin release via stimulation of JG beta-1 receptors
Hormonal response to low CO
•RAA Axis: Decreased renal artery perfusion pressure due to reduced CO, decreased salt delivery to macula densa, and stimulation of JG beta-1 receptors by SNS Increased renin secretion from granular cells in JG apparatus Renin converts angiotensinogen to angiotensin I Angiotensin I (via ACE) Angiotensin II
o Vasoconstriction
o Increased intravascular volume by stimulating thirst via hypothalamus, increased aldosterone from adrenal cortex (increased sodium/water resorption at distal convoluted tubule)
o Increased ADH secretion from posterior pituitary – more water resorption by increased water retention in the distal nephron, and systemic vasoconstriction.
Endothelins
Natriuretic peptides - decrease in low CO
o Released in response to increased intracardiac pressure by atrial cells (Mechanoreceptors triggered by stretch, release ANP). Ventricular cells release BNP by the same means.
o Stimulate sodium and water excretion (decreased preload)
o Vasodilation – decreased SVR and increased forward CO (less afterload)
o Inhibition of renin secretion
o Antagonizes effects of angiotensin II (see above)
Sx of L-sided HF
exertional dyspnea - pulmonary congestion & decreased forward flow (compress airway, J receptor –> shallow, rapid breathing), accumulation of lactic acid
Dulled mental status
Decreased urine output and nocturia (renal perfusion at night)
Orthopnea
Paraoxysmal nocturnal dyspnea (severe breathlessness 2-3 hours into sleep)
Hemoptysis - rupture of engorged bronchial veins
Fatigue
Sx of R-sided HF
Right upper quadrant discomfort (liver engorgement, edema within GI tract –> anorexia and nausea)
peripheral edema