Pulmonary valve
Three semilunar cusps at the top of the right ventricle that open to let blood out to the lungs and shut so that none falls back in.
What it normally does
The right ventricle pumps into a low-pressure circuit — normal pulmonary artery pressure is about 25/10 mmHg (mean around 14 mmHg), roughly a fifth of aortic systolic pressure — so its free wall is thin, about 3 to 5 mm. A thin-walled pump copes with extra volume for years but tolerates extra pressure badly.
narrowing the pulmonary valve loads that thin ventricle with pressure, so it hypertrophies, stiffens and eventually fails — while a valve that leaks loads it with volume, which it can absorb silently for decades.
Blood leaves the right ventricle through a muscular funnel (the right ventricular outflow tract, or infundibulum) and then through the three cusps. Obstruction can sit below the cusps in that muscle, at the cusps, or above them in the pulmonary artery and its branches. Where it sits decides the fix: balloon valvuloplasty for the typical thin domed valve, surgical resection for fixed muscular subvalvular obstruction, and usually catheter balloon angioplasty with stenting (surgery in selected cases) for supravalvular and branch pulmonary artery stenosis.
a beta blocker relieves nothing fixed — it can only settle muscle that is contracting too hard, which is why it works in a tetralogy spell and not in a fused congenital valve; and it explains why a thick dysplastic valve, as in Noonan syndrome, responds poorly to a balloon and often needs surgery.
The valve opens when right ventricular pressure rises above pulmonary artery pressure and shuts when it falls below; that closure is the pulmonary component of the second heart sound (P2). Flow becomes turbulent, and so audible, when it moves fast enough — which happens either because the orifice is narrowed or because the volume crossing a normal valve is high.
a systolic murmur at the upper left sternal edge does not by itself mean valve disease: the same sound is produced by a normal valve carrying a large flow, and separating the two rests on the company the murmur keeps rather than on the murmur alone.
Normally the split second heart sound widens on inspiration (P2 delayed as the right ventricle takes longer to empty a larger volume) and narrows on expiration. Anything that further delays right ventricular emptying delays P2 further, so pulmonary stenosis gives a wide split that still moves with breathing, with P2 progressively later and softer as the valve tightens.
the pattern of the split, not the murmur, does the diagnostic work: wide and still moving points to pulmonary stenosis, wide and fixed to an atrial septal defect, and an inaudible P2 to severe stenosis.
Breathing in draws more blood into the right heart, so most right-sided murmurs and sounds get louder with inspiration (when this inspiratory increase is used to identify the murmur of tricuspid regurgitation it is called Carvallo sign). The classic exception is the pulmonary ejection click of valvular pulmonary stenosis, which softens on inspiration.
inspiration is the bedside test for whether a systolic murmur arises on the right or the left side of the heart, and the click that behaves the opposite way points specifically at a mobile domed valve.
What goes wrong
- Congenital valvular pulmonary stenosis← from “The right ventricle pumps into a low-pressure …”
The cusps fail to separate fully in development and fuse into a dome with a small central hole. To push the same stroke volume through that hole the thin right ventricle must generate a much higher systolic pressure — 60, 80, sometimes over 100 mmHg. It hypertrophies, becomes stiff and fills poorly, and after years of pressure load it dilates and fails.
After bicuspid aortic valve the commonest congenital valve lesion; ejection systolic murmur plus ejection click that softens on inspiration; severe on Doppler is a peak gradient above about 64 mmHg (peak velocity over 4 m/s); balloon valvuloplasty is the treatment for the typical domed valve, and a dysplastic Noonan valve is the one that resists it.
You would find: Harsh ejection systolic murmur at the upper left sternal edge, louder on inspiration, radiating towards the left shoulder and back, often with a palpable thrill and an ejection click. The tighter the valve, the longer the murmur, the later it peaks, and the softer and later P2 becomes. Severe disease adds a giant a wave in the JVP, a left parasternal heave, and exertional breathlessness or syncope. It is usually picked up as a murmur at a routine child health check.
- Outflow obstruction in tetralogy of Fallot← from “Blood leaves the right ventricle through a mus…”
Most of the obstruction here is the muscular funnel below the valve, plus a small valve — and muscle can spasm. Pair that with a hole between the ventricles. When outflow resistance rises above systemic resistance, blood takes the easier exit and goes right-to-left through the ventricular septal defect instead of to the lungs, so the child turns blue.
Dynamic muscular obstruction, so it is the one pulmonary outflow lesion drugs can shift: knee-to-chest or squatting, oxygen, fluid, then an alpha-1 agonist to raise systemic resistance and a beta blocker to relax the infundibulum. Quieter murmur equals worse spell.
You would find: In a spell the baby gets bluer and the murmur gets quieter, because less blood is crossing the outflow, not more — a quiet murmur here is bad news rather than reassurance. Squatting raises systemic resistance and pushes blood back towards the lungs, so the child pinks up and the murmur becomes louder again.
- Pulmonary regurgitation (the valve leaks backwards)← from “The right ventricle pumps into a low-pressure …”
The cusps no longer seal in diastole, so blood falls back into the right ventricle. Two common routes: a pulmonary artery and valve ring stretched by high pressure (pulmonary hypertension), or a valve deliberately opened up — by balloon valvuloplasty, or by cutting across it with a transannular patch at Fallot repair. Because the thin right ventricle tolerates volume far better than pressure, it commonly causes no symptoms for many years while the ventricle slowly dilates, and the murmur can stay short and soft even when the leak is free, so loudness does not track severity here.
Volume load, not pressure load, so it is silent long after it is severe; severity is judged by right ventricular volume on MRI rather than by murmur intensity; transannular-patch Fallot repair is the classic cause and the classic reason for a later pulmonary valve replacement.
You would find: Soft early diastolic murmur at the upper left sternal edge, louder on inspiration (called the Graham Steell murmur when it is driven by pulmonary hypertension). Adults repaired for Fallot with a transannular patch nearly all carry significant regurgitation and are followed in an adult congenital clinic with right ventricular volumes tracked on cardiac MRI to time pulmonary valve replacement. After balloon valvuloplasty for isolated stenosis the leak is usually mild, but it is followed for the same reason.
- A flow murmur that is not valve disease← from “The valve opens when right ventricular pressur…”
The murmur comes from turbulence, and turbulence rises with flow as well as with narrowing. Fever, anaemia, pregnancy, an athletic heart, or an atrial septal defect shunting extra blood through the right heart can all produce a murmur across a structurally normal pulmonary valve.
Soft, no thrill, no click, normal moving split, and nothing else abnormal: innocent. Fixed split means atrial septal defect; a thrill, a click, or a late-peaking murmur means look at the valve.
You would find: A flow murmur is soft (grade 2/6 or less), has no thrill and no ejection click, and S2 splits normally — widening on inspiration and narrowing on expiration. An atrial septal defect gives fixed splitting that does not move with breathing, and that single finding separates them. In an Aboriginal or Torres Strait Islander child most murmurs are still innocent, but a new apical systolic murmur must be treated as possible rheumatic mitral regurgitation until excluded — acute rheumatic fever very rarely involves the pulmonary valve, and these communities carry some of the highest rates of rheumatic heart disease in the world.
What we give, and how it works
Open a drug to see what it binds, what that does to the cell, and what you then see in the patient.
- Binds
- EP4 prostaglandin receptors on ductal smooth muscle.
- Which does
- Receptor stimulation raises cyclic AMP in the smooth muscle cell, which relaxes it and prevents the postnatal constriction and closure of the duct.
- So you see
- The duct stays open, so systemic blood reaches the pulmonary arteries and saturations rise in a duct-dependent pulmonary circulation.
- And the same mechanism causes
- The same vasodilatation and smooth-muscle relaxation elsewhere causes hypotension, flushing and fever, and central prostaglandin effects cause apnoea — most likely in the first hours and in small or preterm babies, which is why the airway is prepared in advance.
- Handling
- Continuous intravenous infusion, because its plasma half-life is only minutes and much of it is cleared on a single pass through the lungs — stopping the infusion lets the duct close within hours.
Catches people out: Apnoea is common and can be sudden, so continuous monitoring and someone ready to support the airway are needed before the infusion starts. It helps only if lung blood flow is actually duct-dependent.
- Binds
- Beta-1 adrenoceptors on infundibular and general myocardium (propranolol also beta-2 on bronchial and vascular smooth muscle).
- Which does
- Blocks catecholamine-driven Gs signalling, so cyclic AMP and calcium entry fall and the infundibular muscle contracts less forcefully and more slowly.
- So you see
- The dynamic subvalvular narrowing widens and heart rate falls, so more blood goes forward to the lungs and less shunts right-to-left; the child pinks up and the outflow murmur returns.
- And the same mechanism causes
- Because the same receptors sit elsewhere, negative inotropy and bradycardia can drop cardiac output and blood pressure, and non-selective propranolol blocks bronchial beta-2 receptors and can provoke bronchospasm in a wheezy child.
- Handling
- Esmolol is used when the effect must be titrated fast or withdrawn quickly — it is hydrolysed by red cell esterases with a half-life of about 9 minutes, so an adverse response wears off in minutes.
Catches people out: It helps obstruction that is made of contracting muscle. A fused congenital valve is a fixed orifice — no drug opens it, and reducing contractility in that setting simply drops output.
- Binds
- Alpha-1 adrenoceptors on vascular smooth muscle of systemic arterioles.
- Which does
- Gq coupling raises intracellular calcium and constricts the arteriole.
- So you see
- Systemic vascular resistance and blood pressure rise, the pressure balance across the ventricular septal defect reverses, and shunting swings back towards the lungs, so saturations rise and the outflow murmur becomes louder again.
- And the same mechanism causes
- The rise in blood pressure triggers a baroreceptor reflex bradycardia, and unopposed vasoconstriction can raise afterload excessively and reduce peripheral and, with extravasation of a peripheral infusion, local tissue perfusion.
Catches people out: The mirror image is the danger: anything that drops systemic blood pressure during a cyanotic spell — vasodilators, or deep sedation without support — increases right-to-left shunting and the child becomes bluer.
- Binds
- The luminal Na-K-2Cl cotransporter (NKCC2) in the thick ascending limb of the loop of Henle.
- Which does
- Blocking the cotransporter stops sodium, potassium and chloride reabsorption and abolishes the medullary concentration gradient, so a large sodium and water load reaches the collecting duct and is excreted.
- So you see
- Diuresis with falling venous filling pressure — oedema, ascites and hepatic congestion settle and breathlessness eases.
- And the same mechanism causes
- Delivering sodium distally drives potassium and hydrogen ion loss, giving hypokalaemia and metabolic alkalosis, along with hyponatraemia, hypomagnesaemia and hypovolaemia; the same cotransporter in the inner ear explains the tinnitus and hearing loss seen with high or rapidly infused doses.
- Handling
- It works from inside the tubule after being secreted by the proximal organic anion transporter, so its effect falls off when renal blood flow is poor or when other organic anions compete for that transporter.
Catches people out: It treats the congestion, not the obstruction. A thick, stiff right ventricle depends on a high filling pressure, so over-diuresis can drop cardiac output and blood pressure quickly.
- Binds
- Penicillin-binding proteins (bacterial transpeptidases) in the streptococcal cell wall.
- Which does
- Acylation of the transpeptidase blocks peptidoglycan cross-linking, so a growing organism builds a defective wall and lyses.
- So you see
- The transient bacteraemia that follows a dental procedure is reduced and its organisms killed, so fewer reach and colonise prosthetic valve material.
- And the same mechanism causes
- Beta-lactam allergy ranges from a delayed rash to anaphylaxis, and killing commensal flora as well as the target organism causes diarrhoea and can allow Clostridioides difficile overgrowth — the reason exposure is confined to a single dose in a narrow group.
Catches people out: Prophylaxis is limited to the high-risk list: prosthetic valve or prosthetic material used in valve repair, previous infective endocarditis, unrepaired cyanotic congenital heart disease, congenital disease repaired with prosthetic material within the previous 6 months, repaired disease with a residual defect at or adjacent to prosthetic material, a transplanted heart with valvulopathy, and rheumatic heart disease in Aboriginal and Torres Strait Islander people. Some repaired Fallot patients qualify on the residual-defect criterion; isolated pulmonary stenosis does not. Daily dental hygiene prevents more endocarditis than any single dose.
Most right-sided sounds get louder with inspiration; the pulmonary ejection click of valvular pulmonary stenosis is the classic exception, becoming softer, because inspiration has already pushed the domed valve part-open so it has less excursion left to snap. Then read the second heart sound: a wide split that still moves with breathing means pulmonary stenosis, a wide split that does not move at all means atrial septal defect, and a P2 you cannot hear means the stenosis is severe.
Now test whether it stuck
Reading this through is not the same as being able to reconstruct it. Every question in the bank is free, with a full debrief on each option.