Heart Flashcards
What is heart failure
Inability to provide adequate output to support needs of the tissue
What are normal circulation values
Systemic veins: 5mmHg
Pulmonary artery: 30mmHg
Pulmonary veins: 8mmHg
Aorta: 100mmHg
What do baroreceptors do
In the aorta and bifurcation of the carotids - ensure aortic pressure is cosntant
What is right sided heart failure
Cannot pump blood effectively into pulmonary circulation. Blood backs up behind right ventricle. Only systemic venous pressure changes to 10mmHg as right ventricular end-diastolic pressure increases
What is left sided heart failrue
Impaired pumping causes CO to fall to 6mmHg. Blood backs up in to the left side of heart. Pulmonary venous pressure rises because left end-diastolic pressure is increased. Elevated venous pressure transmitted through lungs to increase pulmonary artery pressure
What is congestive heart failure
Failure of left side puts strain on the right. Increase of pulmonary vein pressure due to left side back up, increase of pulmonary artery pressure as lungs back up, increase of systemic veins as right side backs up
What pressure is kept constant
Aortic
What are the three causes of heart failure
Pressure overload, volume overload, contractile dysfunction
What are examples of pressure overload
Hypertension, aortic stenosis - obstruction in the outflow tract
What are examples of volume overload
Aortic or mitral valve regurgitation - ventricles have too much blood at the wrong time
What are examples of contractile dysfunction
Ischaemic heart disease, myocardial disease, pregnancy - changes to hormonal balance, congenital cardiomyopathies)
What is Laplace’s law
For a fixed wall stress, a small ventricle can generate high pressure than a large ventricle. When a heart gets bigger, for the heart to generate the same pressure it must either increase the amount of work done by the fibres or increase the wall thickness
What occurs to heart muscles during pressure overload
Increase in left ventricular pressure -> increase wall stress. Muscles have to work harder to muscles enter concentric hypertrophy (R becomes smaller) -> heart starts to dilate, which further increases wall stress
What occurs to heart muscles during volume overload
Valve regurgitation, increasing radius -> wall stress increases
Wall stress normalised by dilated hypertrophic myocardium -> eventually enters myocardial failure
What occurs to heart muscles during dilated cardiomyopathy
Hypertrophy equals degree of chamber enlargement -> excessive chamber enlarge and inadeqaute hypertrophy
What occurs to heart muscles in hypertrophic cardiomyopathy (normal relation between wall thickness and wall stress)
Development of dilation leads to myocardial failure
What is the normal weight of the heart
Less than 450g in males and less than 400g in females
Ratio of LV/body height should be less than 36
What happens in the cardiac compensatory mechanism
Acute overload -> myocyte growth - hypertrophy -> physiological hypertrophy (normal) or -> concentric hypertrophy (fatter) or eccentric hypertrophy (longer) - these both have increased expression of embryonic genes
What are the 3 phases of heart failrue
Short term acute: functional reserves overwhelmed by overload Compensated hypertrophy (can last up to 10 years): heart enlarges and adapts Chronic failure: exhaustion, cell death and necrosis
Describe the steps of the neurohumoral compensatory mechanism
LV failure -> CO falls -> BP falls -> baroreceptor reflex sympathetic stimulation -> peripheral vasoconstriction and increased HR and contractility -> constriction of renal arteries to retain slat and water -> CO returns to normal and BP returns to normal
Describe the renal compensatory mechanism
Sympathetic stimulation -> renal artery vasoconstriction -> sodium and water retention -> RAAS pathway -> increased CVP -> increased end diastolic pressure
How does the RAAS pathway work
Renin secretion by juxtaglomerular cells kidney -> convert angiotensinogen to angiotensin I -> angiotensin II by ACE -> AGII causes vasoconstriction at tissues and raises blood pressure and releases aldosterone from adrenal lands -> slat and water retention
How do ANPs work
Rise in CNP cause release of ANP. Diuretic action - vasodilates and inhibits aldosterone secretion, noradrenaline release. ANP is an endogenous antagonist for AGII.
Why do the beneficial effects of ANP not dominate
Increase in ANP overwhelmed by vasoconstriction and slat and water retention induced by activation of RAAS. ANP secretion becomes down regulated and vascular ANP receptors desensitised
What are the treatments for heart failure
Beta blockers for sympathetic activation
ACE inhibitors for RAAS
Spironolactone for aldosterone secretion
What are the consequences of cardiac hypertrophy
Increases susceptibility to ischaemia, incidence of arrhythmias, sudden wall.
Increased wall stress -> increased O2 consumption but there is a capillary inadequacy impaired vascular reserve -> O2 imbalance energy crisis -> focal fibrosis, ischaemia, and collagen depo -> decreased contractility and increased stiffness -> LV dilatation -> LV failure
What is the fluid movement on the arterial side of normal capillary
Hydrostatic pressure > colloidal pressure -> loss of fluid into the lymph. Gradient is reversed at distal end and fluid moves back into the vessels. No net loss of fluid movment
What is fluid movement of normal pulmonary circulation
Colloidal > hydrostatic throughout. Net loss of fluid from the lung. Not a problem as we are constantly breathing in humidified air
What is the fluid movement in heart failure
High pulmonary circulation pressure, gradient is reversed. Hydrostatic pressure is higher on the arterial side of the capillary. Net gain of fluid into the lungs
What happens as a result of mild fluid accumulation in the lungs
Dyspnoea Pleural effusion (fluid accumulation in interstitium and pleural spaces). Lungs stiffer, more difficult to breath. Increase pulmonary vascular resistance. Increase PA pressure
What happens as a result of severe fluid accumulation in the lungs
Dyspnoea Pulmonary oedema (fluid accumulation in the alveoli). Reduced volume for gas exchanged. Severe pulmonary congestion. Increase PA pressure increase RA pressure, right heart side heart failure, systemic venous pressure increase
What are the symptoms of angina of effort
Tightness, squeezing, crushing sensation in the chest.
What causes angina of effort
Increased O2 demand with restricted blood flow (particularly in left ventricle due to fixed stenosis)
Decrease O2 in cardiac tissue -> release of proton, bradykinin -> activation of TRPV1 of sensory nerves -> pain, also release of substance P (not enough to overcome effects of stenosis) -> coronary vasodilation
What is bradykinin
Inflammatory mediator, causes blood vessels to dilate and BP to fall. ACE inhibitors increase bradykinin
What is substance P
Involved in vasodilation, inflammation, pain, mood, vomiting, and cell growth
How does heparin work
Activates antithrombin II (AT). AT inactivates thrombin and Xa. LMWH has 4x longer half life.
How does warfarin work
Blocks vitamin K epoxide reductase. Inhibits factors II, VII, IX, and X
What is mixed angina
Unpredictable, develops at different levels of exercise
Probably due to stenosis + vasospasm
What is vasospastic angina
Decreased O2 supply due to spasm of coronary artery, occurs at rest
What is microvascular angina
Chest pain, normally coronary angiogram, positive exercise test, endothelial dysfunction, microvasculature is constricted. More common in women
What is unstable decrease O2 supply angina
Due to transient formation of non-occlusive thrombus, an acute coronary symptom
What is the treatment for immediate relief
Short acting nitrate
What is prophylaxis for angina
- Beta blocker or CCB
- Beta blocker + vascular selective CCB
- Beta blocker + vascular selective CCB + long acting nitrate or ivabradine, nicroandil, ranolazine
How do you diagnose angina
Myocardial perfusion scan, MRI, Echo, US
How do nitrates work
Decrease CVP through dilating veins - reduces size of heart, decreasing wall tension
Release NO
Activates ATP driven Ca2+ pumps. Ca2+ densitization also occurs