心血管・OET 待命 24 小時

Congenital heart disease becomes more intelligible when anatomical labels are connected to a physiological question: how does the abnormality alter the direction, volume and oxygen content of blood flow? The direction of a shunt decides whether a child is cyanosed, because only a right-to-left passage delivers deoxygenated blood into the systemic circulation, whereas the position of a shunt decides which chambers enlarge. A ventricular septal defect therefore loads the left heart, an atrial septal defect loads the right heart and fixes the splitting of the second sound, and a persistent arterial duct hums its continuous machinery murmur beneath the left clavicle. Map the flow, and the murmurs fall into line.

Transposition of the great arteries rewrites that map more radically than any hole. Because the aorta arises from the right ventricle and the pulmonary artery from the left, the two circulations run in parallel rather than in series: oxygenated blood circles the lungs indefinitely, while desaturated blood is pumped, undisturbed, around the body. Survival depends entirely on mixing through the foramen ovale, the arterial duct or a coexisting septal defect, and this physiology explains the two bedside signs that first raise suspicion. A hyperoxia test fails, the arterial oxygen tension remaining below approximately 100 mmHg despite 100 per cent oxygen, because supplemental oxygen never reaches the systemic loop. Furthermore, when pulmonary vascular resistance stays high, oxygenated pulmonary-artery blood streams through the duct into the descending aorta, so the feet are pinker than the hands: reverse differential cyanosis, a sign almost unique to transposition.

Management follows from fetal physiology reversed. The duct remains open in utero under the influence of prostaglandin and closes after birth as prostaglandin falls; consequently, prostaglandin E1 infused at 0.05 micrograms per kilogram per minute maintains it, whereas indomethacin or ibuprofen closes it in the preterm infant. Apnoea, fever and flushing are the expected side effects, so airway equipment belongs at the bedside before any retrieval. When the atrial septum is restrictive, a Rashkind balloon atrial septostomy tears a larger communication and buys the mixing that no infusion can provide.

Timing then becomes the whole argument. The arterial switch operation must be completed within roughly two weeks of birth, because a left ventricle that ejects only into the low-pressure pulmonary circuit rapidly loses mass and contractile reserve; beyond that window it cannot sustain systemic pressure, and even a flawless anatomical repair fails for want of a pump. Timing governs the acyanotic lesions too. A small ventricular septal defect is loud precisely because it is restrictive, preserving the pressure gradient that drives a fast jet, whereas a large defect equalises pressures, murmurs quietly and seeds pulmonary vascular disease. Closure is indicated when the pulmonary-to-systemic flow ratio exceeds 2 to 1, yet once Eisenmenger physiology has fixed the resistance and reversed the shunt, closure is contraindicated, for the defect has become the right ventricle's only relief valve.

The central distinctions can be recalled as follows.

All cyanosis that ignores 100 per cent oxygen is cardiac until proven otherwise, and prostaglandin E1 is started before the anatomy is confirmed.
Is the right hand bluer than the left foot? Then suspect transposition with a patent duct and high pulmonary resistance.
On a restrictive atrial septum, balloon atrial septostomy restores mixing the same day.
Luminal patency of the duct is only a bridge, and the arterial switch must follow within two weeks, before the left ventricle deconditions.

Aortic aneurysm and dissection represent distinct forms of structural failure: progressive dilatation increases rupture risk, whereas disruption of the wall can allow blood to separate its layers. Laplace's law governs the first: wall tension is proportional to radius multiplied by pressure, so as an aneurysm widens the same blood pressure generates ever greater tension, growth accelerates and rupture approaches. Surgical thresholds follow from this physics. An ascending thoracic aneurysm is repaired at 5.5 cm, a descending aneurysm at 6 cm, and an abdominal aneurysm at 5.5 cm in men or 5.0 cm in women, whereas patients with Marfan syndrome, Loeys-Dietz syndrome or a bicuspid aortic valve are operated on earlier, at 4.5 to 5.0 cm, because their media is fragile. Growth of a centimetre a year, or symptoms, also brings surgery forward. A 4 cm descending aneurysm, by contrast, is watched with annual CT angiography, since transthoracic echocardiography cannot visualise the distal descending aorta.

Abdominal aneurysms arise most often below the renal arteries, where atherosclerosis, smoking, male sex and age converge; consequently, men aged 65 to 75 who have ever smoked are offered a single screening ultrasound. Rupture announces itself with abdominal or back pain, hypotension and a pulsatile mass, and a complete triad sends the patient to theatre rather than the scanner.

The acute aortic syndromes share sudden tearing pain, pulse deficits and an inter-arm pressure difference, yet they differ in anatomy. Classic dissection begins with an intimal tear through which blood enters the media and carves a false lumen, seen on CT angiography as a flap between two channels; intramural haematoma follows rupture of the vasa vasorum and appears as crescentic wall thickening without a flap; a penetrating atherosclerotic ulcer erodes through the intima and may progress to either. Hypertension is the commonest predisposition, followed by connective tissue disease, a bicuspid valve, pregnancy and cocaine, whereas sick sinus syndrome, a disorder of rhythm, has no bearing on wall stress. Because the pain mimics infarction, the ECG and troponin are checked before any antithrombotic is given.

Anatomy then dictates treatment. A Stanford type A dissection involves the ascending aorta and demands emergency surgery, because the flap can occlude a coronary ostium, disrupt the aortic valve or rupture into the pericardium within minutes. A type B dissection, confined to the aorta beyond the left subclavian artery, is managed medically unless malperfusion, rupture, rapid expansion or refractory pain declares it complicated, when endovascular stent grafting is indicated.

Medical management targets not pressure alone but dP/dt, the rate at which each systole loads the wall. A vasodilator given first provokes reflex tachycardia and steepens that slope, so a beta-blocker such as esmolol or labetalol is started first, the heart rate is brought to 60 or below, and only then is nitroprusside or glyceryl trinitrate added to hold the systolic pressure between 100 and 120 mmHg. Slow the heart, then soften the pressure, and the tear stays where it is.

The central distinctions can be recalled as follows.

All dissections begin with a beta-blocker, because dP/dt rather than pressure alone extends the tear.
Is the ascending aorta involved? Then it is Stanford type A and needs emergency surgery, whereas an uncomplicated type B stays on medical therapy.
On abdominal aneurysms, repair follows 5.5 cm in men and 5.0 cm in women, and men aged 65 to 75 who have ever smoked receive one screening ultrasound.
Lumen, true and false, divided by an intimal flap on CT angiography defines dissection, whereas crescentic wall thickening without a flap defines intramural haematoma.

The initial assessment of an arrhythmia must establish its haemodynamic consequences before the electrocardiographic pattern is considered in isolation. The clinician asks whether the rhythm has compromised perfusion: hypotension, altered consciousness, ischaemic chest pain, acute pulmonary oedema or shock. Any one of these marks the patient as unstable, and the answer is immediate synchronised cardioversion; pulseless ventricular tachycardia or ventricular fibrillation, having no R wave to synchronise to, is defibrillated instead. A patient who is alert with a preserved blood pressure is stable, and time becomes an ally.

For stable supraventricular tachycardia the sequence exploits the dual innervation of the atrioventricular node. Vagal manoeuvres slow nodal conduction and interrupt the re-entrant circuit; the modified Valsalva, a fifteen-second strain followed immediately by lying flat with the legs raised, terminates roughly four episodes in ten, more than double the traditional posture. If that fails, adenosine at 6 mg and then 12 mg, pushed rapidly, blocks the node for seconds, then verapamil or a beta-blocker follows.

Torsades de pointes tells a tidy causal story. Thiazide and loop diuretics waste potassium and magnesium; delayed ventricular repolarisation prolongs the QT interval; early afterdepolarisations emerge on the tail of the action potential; and an ectopic beat landing on the T wave launches polymorphic ventricular tachycardia. Intravenous magnesium sulfate, 2 g, comes first even when the serum level is normal, because it stabilises calcium channels and silences the trigger; potassium is replaced to above 4.0 mmol/L; and refractory cases are treated by accelerating the heart with isoprenaline or overdrive pacing at 100 to 120 beats per minute, which shortens the QT interval. Class Ia and class III agents, amiodarone included, lengthen the QT further and are avoided, whereas a pulseless patient is defibrillated.

Atrial fibrillation threatens through the clot rather than the rate. The CHA2DS2-VASc score awards two points each for age 75 or above and for prior stroke, and one each for heart failure, hypertension, diabetes, vascular disease, age 65 to 74 and female sex, so a 76-year-old woman with hypertension and diabetes scores five. Anticoagulation is recommended from two points in men and three in women, with a direct oral anticoagulant preferred except in rheumatic mitral stenosis or with a mechanical valve, where warfarin is mandatory; aspirin alone is no longer acceptable.

The node explains the remaining traps. Inhibited by the vagus, excited by sympathetic tone and supplied by the right coronary artery, it is blocked by inferior infarction, hyperkalaemia, beta-blockers, verapamil and digoxin, whereas thyrotoxicosis accelerates it and alpha-blockers never touch it. A transplanted heart is denervated, so atropine cannot release a brake that was never connected, and isoprenaline or pacing is required. Mobitz type I lengthens the PR interval until a beat drops and is usually benign, whereas Mobitz type II drops beats without warning from below the node and, like complete heart block, needs a permanent pacemaker.

Four sentences hold the station together.

All unstable tachyarrhythmias receive synchronised cardioversion, whereas stable supraventricular tachycardia is treated with vagal manoeuvres and then adenosine.
Is the QT prolonged and the rhythm twisting? Give 2 g of intravenous magnesium first, replace potassium, and never add a class Ia or class III drug.
On CHA2DS2-VASc, a 76-year-old woman with hypertension and diabetes scores five and needs a direct oral anticoagulant rather than aspirin.
Lung function testing adds nothing to the evaluation of cardiac syncope, which rests on the ECG, echocardiography, ambulatory monitoring and electrophysiological study.

An early electrocardiogram helps direct the assessment of acute chest pain, while symptoms, serial findings and the wider clinical context determine the next steps. ST elevation signals complete coronary occlusion by a fibrin-rich thrombus and demands immediate reperfusion: primary percutaneous coronary intervention with a door-to-balloon time below 90 minutes where a catheter laboratory exists, or fibrinolysis within 30 minutes where it does not. The laboratory is activated when the ECG is read, never after troponin returns, because every hour of delay converts salvageable myocardium into scar. Without ST elevation, a raised troponin defines non-ST-elevation infarction and a normal troponin unstable angina, and invasive timing then follows risk: within 2 hours for haemodynamic instability, within 24 hours for a GRACE score above 140, and within 72 hours for intermediate risk.

Beneath the ECG lies a ruptured plaque. Exposed collagen and tissue factor summon platelets, which adhere through von Willebrand factor and glycoprotein Ib, activate by releasing adenosine diphosphate and thromboxane A2, and aggregate when the glycoprotein IIb/IIIa receptor changes shape; because that receptor cannot bind its neighbour directly, fibrinogen must bridge each pair of platelets. Each antiplatelet class severs one link: aspirin irreversibly inhibits cyclo-oxygenase-1, clopidogrel and ticagrelor block the P2Y12 receptor, abciximab, eptifibatide and tirofiban occupy glycoprotein IIb/IIIa, and vorapaxar antagonises the thrombin receptor PAR-1.

The right ventricle rewrites the rulebook. Because the right coronary artery supplies both the inferior wall and the right ventricle, an inferior infarction may disable a thin-walled chamber whose contractile force is roughly one sixth of the left ventricle's a passive conduit steeply dependent on preload. The triad of hypotension, distended neck veins and clear lung fields, confirmed by ST elevation of 1 mm or more in V4R, therefore inverts the treatment of left heart failure: nitrates, morphine and diuretics, which all reduce preload, are contraindicated, whereas 1 to 2 litres of intravenous saline restores right ventricular filling, dobutamine follows if fluid fails, and reperfusion of the right coronary artery remains the definitive cure.

Valve disease answers two questions: does the murmur fall in systole or diastole, and does blood fail to pass a valve that should open or leak through one that should close? Mitral stenosis produces a low-pitched mid-diastolic rumble with an opening snap, loudest at the apex with the bell in the left lateral position, and it depends on diastolic time for filling. Pregnancy attacks both vulnerabilities at once, raising plasma volume by roughly 50 per cent and accelerating the heart rate, so the transvalvular gradient and left atrial pressure climb until pulmonary oedema follows; hence mitral stenosis carries the highest maternal cardiac mortality of any valve lesion.

Management slows the heart with a beta-blocker, restricts salt, and turns to percutaneous balloon valvuloplasty when symptoms persist, while ACE inhibitors and angiotensin receptor blockers are contraindicated in pregnancy.

The central distinctions can be recalled as follows.

All ST-elevation infarctions activate the catheter laboratory on the ECG alone, with a door-to-balloon target of 90 minutes and oxygen only below 90 per cent saturation.
Is the jugular pressure raised while the lungs stay clear in an inferior infarction? Then record V4R, give fluids, and withhold nitrates, morphine and diuretics.
On the platelet, fibrinogen bridges glycoprotein IIb/IIIa receptors, which is why abciximab blocks aggregation at its final step.
Lung congestion in late pregnancy with a diastolic rumble and an opening snap means mitral stenosis decompensating under 50 per cent more volume and a faster heart, treated with a beta-blocker, salt restriction and, if refractory, balloon valvuloplasty.

Cardiac symptoms may originate in the pericardial sac, the myocardium or the circulation it supports; distinguishing these sites explains why superficially similar presentations require different responses. Acute pericarditis, most often idiopathic or viral, carries a fingerprint that follows directly from anatomy. The inflamed layers rub against each other, producing a high-pitched scratching friction rub; lying flat presses the heart onto the inflamed surface, whereas sitting forward relieves it. Because the entire epicardium is involved rather than one coronary territory, the electrocardiogram shows widespread concave ST elevation with PR depression and no reciprocal change.

Treatment targets the inflammation itself. A non-steroidal anti-inflammatory drug relieves pain, colchicine markedly reduces recurrence, and corticosteroids are withheld from first-line therapy because they paradoxically increase relapse; they are reserved for autoimmune or uraemic disease or refractory cases. Troponin may rise modestly when the subepicardial myocardium is involved, yet never to the multiples seen in infarction.

Tamponade and constriction squeeze the same organ in different ways. Rapidly accumulating fluid prevents diastolic filling, so output falls and venous return backs up: hypotension, distended neck veins and muffled heart sounds form Beck's triad. On inspiration the enlarging right ventricle pushes the septum leftwards, and systolic pressure falls by more than 10 mmHg, the pulsus paradoxus of tamponade. Constriction, by contrast, is a slow fibrotic shell that follows tuberculosis, radiotherapy or surgery; filling halts abruptly against the rigid wall, producing a dip-and-plateau trace, a steep Y descent and a pericardial knock. Kussmaul's sign belongs to constriction, right ventricular infarction and severe tricuspid regurgitation, yet is absent in tamponade. Consequently, tamponade demands urgent pericardiocentesis, constriction is cured by pericardiectomy, and diuretics, helpful in constriction, are hazardous in tamponade.

Heart failure is classified by ejection fraction: reduced below 40 per cent, mildly reduced from 41 to 49 per cent, and preserved at 50 per cent or above. In the reduced phenotype, compensation by the renin-angiotensin-aldosterone and sympathetic systems ultimately drives remodelling and fibrosis. The four pillars of guideline-directed therapy suppress precisely these pathways: an angiotensin receptor-neprilysin inhibitor, one of three evidence-based beta-blockers (carvedilol, bisoprolol or metoprolol succinate), a mineralocorticoid receptor antagonist and an SGLT2 inhibitor, which helps with or without diabetes. Loop diuretics and digoxin relieve congestion without prolonging life, whereas verapamil and diltiazem are contraindicated because their negative inotropy depresses an already failing pump.

The natriuretic peptides explain the third patient's alarm. Ventricular stretch releases BNP, which promotes natriuresis and vasodilatation before neprilysin degrades it. Sacubitril inhibits neprilysin, so measured BNP rises even as the heart improves, whereas NT-proBNP, the inactive fragment of the same precursor, is not a neprilysin substrate and falls with successful treatment. Context matters too: adipose tissue clears BNP through the NPR-C receptor, so obesity lowers readings, while renal impairment, age, female sex and atrial fibrillation raise them.

From sac to muscle to pump, the night's three beds trace one line, and four sentences carry its examinable core.

All chest pain that changes with posture, with widespread concave ST elevation and PR depression, is pericarditis until proven otherwise.
Is Kussmaul's sign present? Then the cause is a rigid right heart, constriction, right ventricular infarction or tricuspid regurgitation, never tamponade.
On sacubitril-valsartan, BNP rises because neprilysin is blocked, so response is followed with NT-proBNP.
Lung congestion yields to diuretics, but only the four pillars prolong survival in heart failure with reduced ejection fraction.

Dyslipidaemia and hypertension may remain asymptomatic while cardiovascular risk accumulates; their numerical measurements become meaningful when linked to underlying physiology and long-term outcomes. Lipoproteins form a transport fleet. Chylomicrons carry dietary triglyceride from the gut and hepatic VLDL carries endogenous triglyceride, both unloading in peripheral capillaries through lipoprotein lipase; what remains of VLDL becomes cholesterol-rich LDL, cleared by hepatic LDL receptors, whereas HDL runs the reverse route, esterifying scavenged cholesterol through LCAT and returning it to the liver.

Xanthomas reveal which lipid is raised. When LDL is very high, as in familial hypercholesterolaemia with defective LDL receptors, cholesterol seeps into the Achilles and extensor tendons as firm, fixed nodules; when triglycerides exceed about 1,000 mg/dL, macrophages engorged with chylomicron remnants erupt as crops of small papules. The eruptive pattern signals a different emergency, since such levels precipitate acute pancreatitis; a fibrate, which activates PPAR-alpha and lipoprotein lipase, therefore takes priority over any statin, and bile-acid sequestrants are avoided because they raise triglycerides further.

Statins inhibit HMG-CoA reductase, depleting hepatocyte cholesterol and up-regulating LDL receptors so that circulating LDL is drawn from the blood. Intensity means the reduction achieved, not the milligram dose: high-intensity therapy lowers LDL by at least 50 per cent, and very-high-risk patients are treated towards targets below 1.4 mmol/L under the 2019 ESC guideline. Myopathy, attributed to depletion of coenzyme Q10 downstream of mevalonate, becomes likelier when CYP3A4 is inhibited by grapefruit juice or macrolides; rosuvastatin and pravastatin escape that pathway. PCSK9 degrades LDL receptors, so loss-of-function variants confer lifelong low LDL, the rationale for evolocumab and alirocumab.

Hypertension thresholds differ, 130/80 mmHg under ACC/AHA 2017 and 140/90 mmHg under the ESC, yet the logic is shared: treatment begins where lowering pressure lowers events, confirmed by repeated or home measurement. A young patient resisting three drugs, particularly with unexplained hypokalaemia and metabolic alkalosis, points towards primary aldosteronism, screened with the aldosterone-renin ratio once interfering drugs have been substituted.

Two paradoxes complete the chapter. In bilateral renal artery stenosis, glomerular filtration is propped up by angiotensin II constricting the efferent arteriole; an ACE inhibitor removes that prop, filtration collapses and creatinine doubles; bilateral stenosis is therefore a contraindication, whereas unilateral disease is usually tolerated. Second, 200/118 mmHg without acute organ damage is an urgency treated with oral agents over hours to days, whereas an emergency with encephalopathy, acute coronary syndrome, pulmonary oedema or dissection needs titratable intravenous therapy that lowers mean arterial pressure by no more than 25 per cent in the first hour, since cerebral autoregulation has shifted upwards and a precipitous fall causes ischaemia. Dissection is the exception, driven rapidly to a systolic pressure of 100 to 120 mmHg, and pregnancy relies on labetalol, nifedipine or methyldopa because ACE inhibitors are teratogenic.

Read the numbers along their causes and the chapter reduces to four lines.

All tendon xanthomas point to a very high LDL, whereas eruptive xanthomas point to triglycerides above 1,000 mg/dL and imminent pancreatitis.
Is creatinine doubling after an ACE inhibitor? Then suspect bilateral renal artery stenosis, in which angiotensin II was holding the efferent arteriole shut.
On a pressure of 200/118 mmHg without organ damage, treat an urgency by mouth, and lower an emergency by no more than a quarter in the first hour.
Luminal narrowing of both renal arteries, resistant hypertension with hypokalaemia, and grapefruit with a CYP3A4 statin are the three traps this station sets.

The long-term performance of a coronary bypass graft depends on both vascular biology and haemodynamics, helping to explain the durability of an internal mammary artery compared with many saphenous vein grafts. Poiseuille's law states that resistance is proportional to viscosity and length and inversely proportional to the fourth power of the radius, so flow rises sixteenfold when the radius doubles and vessel calibre, not heart rate or length, is the circulation's master switch. Mean arterial pressure equals cardiac output multiplied by total peripheral resistance and approximates diastolic pressure plus one third of the pulse pressure, since diastole is the longer phase.

Stroke volume is governed by preload, afterload and contractility. Within limits, a larger end-diastolic volume stretches the sarcomeres and strengthens contraction, the Frank-Starling mechanism, until an overstretched failing ventricle slides down the far side of the curve. Pressure overload from aortic stenosis or hypertension adds sarcomeres in parallel, concentric hypertrophy, whereas volume overload from aortic or mitral regurgitation adds them in series, eccentric dilatation. The baroreflex, sensed at the carotid sinus via the glossopharyngeal nerve and the aortic arch via the vagus and integrated in the nucleus tractus solitarii, corrects pressure within seconds.

Embryology explains the surgeon's landmarks. Of six pairs of pharyngeal arch arteries, the third forms the common and proximal internal carotids, the left fourth becomes the aortic arch, the right fourth the proximal right subclavian, and the sixth gives rise to the pulmonary arteries, the left sixth persisting as the ductus arteriosus. After birth the duct closes as oxygen rises and prostaglandin E2 falls, leaving the ligamentum arteriosum beneath the left recurrent laryngeal nerve; indomethacin closes a persistent duct in the premature infant, whereas prostaglandin E1 keeps it open in duct-dependent lesions.

Conduit biology decides the long-term result. Arterial endothelium continuously secretes nitric oxide and prostacyclin, which inhibit thrombosis and smooth-muscle proliferation, and the internal mammary artery, with the most resilient endothelium of all, remains patent to the left anterior descending artery in more than 90 per cent of patients at ten years. A saphenous vein exposed to arterial pressure develops intimal hyperplasia within months and graft atherosclerosis within years, and only about half to 60 per cent remain open at a decade. The radial artery, now a class I second conduit, spasms unless a calcium-channel blocker is given and needs a target stenosis of at least 70 to 90 per cent, otherwise competitive native flow starves and closes the graft. Harvesting both mammary arteries devascularises the sternum, so poorly controlled diabetes, obesity and advanced age argue against bilateral use, whereas inhaled therapy does not; off-pump surgery conferred no long-term advantage in the ROOBY and CORONARY trials.

In cardiogenic shock, recent ticagrelor is no reason to wait, because lost blood can be replaced while infarcted muscle cannot, and four lines close the station.

All arterial conduits outlast veins because their endothelium secretes nitric oxide and prostacyclin, so the mammary artery to the LAD is the golden graft.
Is the patient diabetic, obese or elderly? Then one mammary artery, not two, protects the sternum from deep wound infection.
On Poiseuille's law, flow varies with the fourth power of the radius, so a halved radius leaves one sixteenth of the flow.
Lumen for lumen, a radial graft needs a target stenosis of at least 70 per cent, and a shocked heart needs surgery now, not in five days.