Heart failure, shock, valvular and myocardial disease

A heart fails when it cannot deliver the output the tissues need, or can do so only by raising its filling pressure. Systolic failure follows loss of contractile muscle or chronic overload (infarction, hypertension, valve disease, dilated cardiomyopathy) and shows as a low ejection fraction; diastolic failure follows a stiff or thickened ventricle (hypertension, hypertrophic and restrictive cardiomyopathy, ageing) that cannot fill without high pressure. On the ventricular function curve the failing heart operates on a lower, flatter line, so extra preload adds little output. The body compensates in three ways. The Frank–Starling mechanism uses the higher end-diastolic volume that follows retained fluid. Sympathetic activation raises rate and contractility within seconds and constricts vessels, but chronic stimulation down-regulates beta receptors and is toxic to myocytes. The kidney, sensing reduced perfusion, activates the renin–angiotensin–aldosterone system and retains salt and water, which raises preload but also causes congestion and oedema, and angiotensin II and aldosterone drive fibrosis and remodelling. The ventricle hypertrophies, which normalises wall stress at first (Laplace) but stiffens the chamber and outgrows its blood supply. Left ventricular failure raises left atrial and pulmonary capillary pressure and presents with dyspnoea, orthopnoea, paroxysmal nocturnal dyspnoea, pulmonary oedema and a third heart sound; right ventricular failure, most often caused by left failure, raises systemic venous pressure and presents with raised jugular venous pressure, hepatomegaly, ascites and peripheral oedema. Decompensation, often triggered by infection, arrhythmia, ischaemia or non-compliance, is the state in which these mechanisms can no longer hold output and congestion worsens.

Shock is inadequate perfusion of the tissues as a whole. Hypovolaemic shock follows loss of blood or plasma; cardiogenic shock follows pump failure, typically a large infarction; obstructive shock follows tamponade, tension pneumothorax or massive pulmonary embolism; distributive shock (septic, anaphylactic, neurogenic) follows vasodilatation that makes the vascular space too large for the volume. In hypovolaemic shock the picture depends on the loss: up to 10 percent of the volume is barely noticed, 20 to 30 percent lowers output and pressure with strong compensation, and beyond about 40 percent the circulation collapses. Compensation is sympathetic: baroreceptor and chemoreceptor reflexes and, in severe cases, the CNS ischaemic response raise heart rate and contractility, constrict arterioles in skin, muscle, gut and kidney to defend pressure and preserve brain and heart, and constrict veins to restore return; the patient is pale, cold, sweating and tachycardic with a low urine output, and the fall in capillary pressure draws interstitial fluid into the blood. In non-progressive (compensated) shock these mechanisms and the slower renal and hormonal responses restore the circulation without treatment. In progressive shock the ischaemia itself feeds back: the heart weakens as coronary flow falls, the vasomotor centre fails, sluggish flow causes microthrombi (disseminated intravascular coagulation), capillaries become leaky, the acidotic and hypoxic cells release lysosomal enzymes and toxins, and the gut releases endotoxin, so output falls further in a vicious circle that only treatment can break. In irreversible shock, cellular ATP is exhausted and tissues are dead; even if pressure is restored the patient dies. Treatment therefore aims to restore volume or pump function before the progressive stage: fluids or blood in hypovolaemia, inotropes and revascularisation in cardiogenic shock, drainage in tamponade, antibiotics and vasopressors in sepsis.

Treatment aims to reduce the work of the failing ventricle, remove congestion, block the harmful neurohormonal compensation and, where necessary, increase contractility. ACE inhibitors (or ARBs) reduce afterload and preload, limit remodelling and prolong life; they are the foundation for every patient with reduced ejection fraction. Beta-blockers (carvedilol, bisoprolol, metoprolol succinate) started at low dose in stable patients block the toxic effect of chronic sympathetic drive, reduce arrhythmias and improve survival, although they can worsen failure if introduced during decompensation. Aldosterone antagonists (spironolactone, eplerenone) reduce fibrosis and mortality in moderate to severe failure, with the risk of hyperkalaemia. Loop diuretics relieve congestion and oedema by reducing preload but do not improve survival; hydralazine with isosorbide dinitrate reduces afterload and preload and helps patients who cannot take ACE inhibitors. Digoxin inhibits the Na+/K+ ATPase, so intracellular sodium rises, the Na+/Ca2+ exchanger removes less calcium, more calcium is stored and released, and contractility increases; it also stimulates the vagus, slowing the sinoatrial rate and atrioventricular conduction, which makes it useful when failure coexists with atrial fibrillation. It is well absorbed, largely excreted unchanged by the kidney, has a half-life of about 36 hours and a narrow therapeutic index; toxicity presents with nausea, vomiting, anorexia, visual disturbance (yellow-green halos), confusion and almost any arrhythmia, classically premature ventricular beats, bigeminy, atrial tachycardia with block and bradyarrhythmias, and is precipitated by hypokalaemia (diuretics), hypercalcaemia, renal impairment and drugs such as quinidine, verapamil and amiodarone that raise its level. Treatment of toxicity: stop the drug, correct potassium and magnesium, atropine or pacing for bradycardia, lidocaine for ventricular arrhythmias and digoxin-specific antibody fragments in serious poisoning; digoxin relieves symptoms and reduces admissions but does not prolong life. In acute decompensation with low output, intravenous beta-1 agonists (dobutamine) or phosphodiesterase inhibitors (milrinone) raise contractility for days, at the cost of arrhythmia and increased oxygen demand, and are a bridge, not a cure.

Infective endocarditis is colonisation of the valves, usually by bacteria, forming vegetations of fibrin, platelets and organisms that destroy the cusps. Acute endocarditis is caused by virulent organisms, above all Staphylococcus aureus, attacks normal valves (intravenous drug users, right-sided tricuspid disease), and kills within weeks if untreated; subacute endocarditis is caused by low-virulence organisms, typically viridans streptococci from the mouth or Enterococcus and Staphylococcus epidermidis on prosthetic valves, seeds previously damaged or congenitally abnormal valves after bacteraemia, and runs for months with fever, malaise and a changing murmur. Diagnosis rests on blood cultures and echocardiography (the Duke criteria). Complications are valve perforation and regurgitation, abscess, heart failure, septic emboli (brain, kidney, spleen, retina), mycotic aneurysms and immune-complex glomerulonephritis; the peripheral signs (Osler nodes, Janeway lesions, splinter haemorrhages, Roth spots) are embolic or immunological. Non-bacterial thrombotic (marantic) endocarditis produces small sterile vegetations in cancer and hypercoagulable states, and Libman–Sacks endocarditis produces sterile vegetations on both surfaces of the mitral and tricuspid valves in systemic lupus erythematosus. Rheumatic fever is an acute immune disease two to four weeks after group A streptococcal pharyngitis: antibodies against the streptococcal M protein cross-react with cardiac myosin and valve tissue (molecular mimicry). Diagnosis uses the Jones criteria: migratory polyarthritis, carditis, subcutaneous nodules, erythema marginatum and Sydenham chorea, with evidence of recent infection. Acute rheumatic carditis is a pancarditis; its pathognomonic lesion is the Aschoff body, a focus of fibrinoid necrosis with lymphocytes, macrophages and Anitschkow (caterpillar) cells, and small verrucous vegetations line the closure line of the valves. Chronic rheumatic heart disease follows repeated attacks: the mitral valve, alone or with the aortic, develops thickened fused commissures (fish-mouth stenosis), shortened chordae and calcification, causing mitral stenosis with atrial fibrillation, left atrial enlargement, thrombus and pulmonary hypertension. Valvular disease in general is classified by valve and by lesion, stenosis (failure to open: rheumatic, calcific degeneration of a bicuspid or ageing aortic valve) or regurgitation (failure to close: rheumatic, endocarditis, mitral valve prolapse from myxomatous degeneration, dilatation of the annulus, papillary muscle rupture after infarction), and by its haemodynamic consequence, pressure overload with concentric hypertrophy in stenosis and volume overload with dilatation in regurgitation.

A cardiomyopathy is a disease of the heart muscle itself, not secondary to coronary, valvular, hypertensive or congenital disease. Dilated cardiomyopathy, the commonest, is a four-chamber dilatation with systolic failure, a low ejection fraction and mural thrombi; causes include genetic mutations (about a third), previous viral myocarditis, alcohol, doxorubicin and other drugs, cobalt, pregnancy (peripartum) and haemochromatosis, and the outcome is progressive failure, emboli and arrhythmia. Hypertrophic cardiomyopathy is an autosomal dominant disease of sarcomeric proteins (beta-myosin heavy chain, myosin-binding protein C) producing massive, usually asymmetric septal hypertrophy with myofibre disarray, a small stiff ventricle with diastolic dysfunction, dynamic outflow obstruction, angina, syncope and a risk of ventricular arrhythmia; it is the leading cause of sudden death in young athletes. Restrictive cardiomyopathy is a stiff, non-compliant ventricle with normal size and systolic function but impaired filling, caused by amyloidosis, sarcoidosis, radiation, endomyocardial fibrosis and Loeffler endocarditis. The pericardium responds to injury with inflammation classified by its exudate: serous (rheumatic fever, lupus, uraemia, viral), fibrinous or serofibrinous (the commonest, after infarction, uraemia, surgery and radiation, with a friction rub and a shaggy bread-and-butter surface), purulent (bacterial spread from the lungs or blood), haemorrhagic (malignancy, tuberculosis, surgery) and caseous (tuberculosis); fibrinous and purulent forms may organise into adhesive or constrictive pericarditis, which encases the heart in a thick fibrous or calcified shell and impairs filling. A pericardial effusion is tolerated if slow, but a rapid collection of even 200 ml causes tamponade with hypotension, raised venous pressure and muffled heart sounds. Primary cardiac tumours are rare: the myxoma, a gelatinous mass on a stalk in the left atrium of adults that may obstruct the mitral valve, embolise and cause constitutional symptoms; the rhabdomyoma of children, associated with tuberous sclerosis; fibroma, lipoma and papillary fibroelastoma. Metastases from lung, breast, melanoma, lymphoma and leukaemia are far commoner than primary tumours and usually involve the pericardium.