Lecture 10.1 - Pathophysiology of Heart Failure PDF

Frank-Starling law in the failing myocardium: ◦Increased venous return to the heart -> increases stroke volume via an increase in contractile strength of the left ventricle ◦The ability of the heart to change stroke volume in response to venous return is called Frank-Starling...

Frank-Starling law in the failing myocardium: ◦Increased venous return to the heart -> increases stroke volume via an increase in contractile strength of the left ventricle ◦The ability of the heart to change stroke volume in response to venous return is called Frank-Starling mechanism ◦In a failing myocardium - this does not happen. There is a physical limit to the relationship between cardiac stretch and contractility ◦Beyond this limit - further increases in preload have a negative effect on stroke volume Heart failure (HF): ◦Complex clinical syndrome resulting from any structural and/or functional impairment of ventricular filling or ejection Acute vs chronic: ◦Acute heart failure: ‣ Characterised by a rapid onset of symptoms and/or signs of heart failure ‣ Requires urgent evaluation and treatment ‣ Most common causes: acute myocardial dysfunction (ischaemic, inflammatory), acute valvulopathy, arrhythmias (Vfib), pulmonary embolism, drugs (e.g. beta blockers) ‣ May present suddenly with cardiogenic shock or subacutely with decompensation of chronic heart failure ◦Chronic heart failure: ‣ Progressive cardiac dysfunction from structural and/or functional cardiac abnormalities ‣ Usually precipitated by conditions that affect the muscle (e.g. cardiomyopathy), vessels (e.g. ischaemic heart disease), valves (e.g. aortic stenosis), or conduction (e.g. atrial fibrillation) ‣ Characterised by progressive symptoms with episodes of acute deterioration ‣ Classified into systolic (HFrEF) or diastolic (HFpEF) Ejection fraction: ◦Stroke volume = volume of blood pumped per beat ~70ml ◦Volume of blood that is present in ventricles at the end of diastole (beginning of systole) (EDV) ~110ml ◦Ejection fraction - fraction of blood that gets pumped compared to the volume of blood that is in the ventricles at the beginning of contraction ‣ EDF = stroke volume/EDV = 70/110 = 64% ‣ Normal ejection fraction ~ 55-70% Systolic HF/HF with reduced ejection fraction (HFrEF): ◦Heart cannot pump enough blood ◦Systolic dysfunction ◦Stroke volume reduced due to reduced contractility ‣ E.g. MI, dilated cardiomyopathy  ◦Reduced ejection fraction ◦Progressive ventricular dilatation or eccentric hypertrophy Diastolic HF/HF with preserved ejection fraction (HFpEF): ◦Reduced filling of the heart ◦Diastolic dysfunction ◦Preserved ejection fraction ◦Associated with concentric hypertrophy ◦Increased stiffness of ventricular walls: ‣ Increased afterload ‣ Reduced preload: MI, constrictive pericarditis, cardiac tamponade Ventricular remodelling in systolic and diastolic heart failure: Right sided heart failure: ◦Reduced contractility - MI ◦Increased afterload ◦Increased preload - pulmonary valve/tricuspid valve regurgitation ◦More commonly develop from left sided heart failure High output vs low output: ◦High output HF: ‣ There is high CO >8L/min ‣ But heart unable to meet increased demand despite normal cardiac function E.g. hyperthyroidism, severe anaemia ‣ Increased demand due to shunting of blood from arterial to venous side AV fistula (usually found in the leg), thiamine deficiency (in chronic alcoholics) Pathophysiology of heart failure: ◦In heart failure, the decreased CO causes a decreased BP (BP = CO x TPR) ◦Reduced BP causes: ‣ Baroreceptors to detect the low BP and stimulate an increase sympathetic drive that leads to: Increased heart rate, increased peripheral resistance - causes decompensated heart failure ◦Activation of the renin-angiotensin-aldosterone system that causes: ‣ Increased sodium retention leading to increased water retention (water follows sodium) and this increases the circulating volume ‣ Anti-diuretic hormone release ‣ Vasoconstriction ◦This is all an attempt to increase the BP but really culminates in an increased afterload and preload which puts even more strain on the failing  heart Signs and symptoms - left sided heart failure: ◦Blood will accumulate in the left atrium and pulmonary veins and pulmonary venous circulation ◦Pulmonary venous pressure increases -> leads to pulmonary congestion as blood backs up from left side to lungs ◦Fluid leaks out into interstitial fluid of pulmonary tissues -> pulmonary oedema ◦Decreased ventilation across alveoli -> hypoxia ◦Severe reduction in CO -> reduced BP -> to compensate this TPR increases (cold/pale extremities) ◦Organ malperfusion can affect brain (encephalopathy), heart (infarction), kidney (acute kidney injury), intestine (acute mesenteric ischaemia) ◦Ischaemia can lead to increased lactic acid -> pH drops triggering acidosis ◦Symptoms: ‣ Dyspnoea ‣ Cough (often dry) ‣ Orthopnoea (difficulty lying flat, so can become breathless) ‣ Paroxysmal nocturnal dyspnoea (waking up breathless at night) ◦Signs: ‣ Crackles/rales on auscultation (bi-basal) ‣ Tachycardia ‣ Cardiomegaly ‣ 3rd and 4th heart sounds Signs and symptoms - right sided heart failure: ◦Increased pressure in pulmonary veins causes difficulty of RV to pump through the pulmonary circulation ◦Either caused by left ventricular failure or respiratory disease ◦If caused by respiratory disease - it is termed 'cor pulmonale' ◦Blood accumulate in the systemic venous circulation -> increased central venous pressure (CVP) as blood backs up into the JVP ◦Symptoms: ‣ Dyspnoea ‣ Chest discomfort ‣ Swelling ◦Signs: ‣ Jugular venous distension ‣ Hepatic congestion ‣ Peripheral oedema ‣ Ascites Signs and symptoms - congestive heart failure: ◦Both the right and left ventricles affected - combination of signs and symptoms ‣ Systemic and pulmonary congestion ◦Symptoms: ‣ Dyspnoea ‣ Cough (often dry) ‣ Orthopnoea (difficulty lying flat) ‣ Paroxysmal nocturnal dyspnoea (waking up breathless at night)  ‣ Chest discomfort ‣ Swelling ◦Signs: ‣ Crackles/rales on auscultation (bi-basal) ‣ Tachycardia ‣ Cardiomegaly ‣ 3rd and 4th heart sounds ‣ Jugular venous distension ‣ Hepatic congestion ‣ Peripheral oedema ‣ Ascites