Jugular veins are jugular veins, pressures are connected directly to t

Jugular veins are jugular veins, pressures are connected directly to the right atrium because why is an upward deflection in the jugular venous pressure, like for example, an A wave is forming because when the right atrium is contracting, contracting, the pressure is going into it's one, when the tricuspid is open, it will be going to the right ventricle and one backward pressure which is going into the neck veins and passing the A deflection. That's why in conditions where there is a problem with tricuspid then or the atrial contraction occurs before the tricuspid opens as in the case of AV dissociations as in maybe AV or block degree 3, there we have complete dissociation between atria and ventricles. Hence there will be cannon A waves because another closed tricuspid valve more back pressure happens and we have a large cannon shaped A waves. So this concept of JVP, why a deflection is coming and how we are measuring and where we are measuring and how are these jugular veins related to the atrium. So the JVP pressures are talking only about the right atrial pressures and the right atrium connecting to the jugular vein or it also happens in the left atrium.

Reading File

Finding Sources

Reading File

Finding Sources

Reading File

Loading Image

Excellent - I now have everything I need for a thorough, authoritative answer. Let me put it all together.

Great question - you've actually laid out the core concept correctly. Let me organize and clarify everything systematically.

Why JVP Reflects Only Right Atrial Pressure (Not Left)

The internal jugular veins drain directly into the superior vena cava, which empties into the right atrium. There are no valves between the internal jugular vein and the right atrium. This means the right atrium's pressure changes are transmitted directly and freely backward into the jugular veins - they act as a simple fluid column connected to the right atrium.

The left atrium has no such direct connection to any visible superficial vein. Its pressures are assessed indirectly via the pulmonary capillary wedge pressure (a catheterization technique), or by echocardiography. So yes - JVP = right atrial pressure only. (Fuster and Hurst's The Heart, 15th Ed.)

The JVP Waveform - Why Each Deflection Occurs

Here is the standard JVP waveform from Medical Physiology (Boron & Boulpaep):

JVP waveform showing a, c, av, x, v, and y components over one cardiac cycle

The waveform has 3 peaks (a, c, v) and 3 troughs (av, x, y):

Wave	Mechanism
a peak	Right atrial contraction - pressure is generated, pushes blood forward into RV (through open tricuspid), and backward into jugular veins
av trough	Right atrial relaxation + tricuspid valve closure
c peak	Early RV systole causes the tricuspid valve (now closed) to bulge back into the right atrium, causing a small pressure rise
x descent	RV contracts and shortens, pulling the tricuspid annulus downward - this physically elongates the atrium and veins, lowering their pressure
v peak	Venous return continues to fill the right atrium while the tricuspid is still closed during ventricular systole - pressure builds passively
y descent	Tricuspid valve opens - blood rushes from right atrium into right ventricle, RA pressure falls rapidly

(Medical Physiology, Boron & Boulpaep)

The A Wave in Detail - Your Question's Core

The a wave is an upward deflection because right atrial contraction generates pressure that has two exit routes:

Forward - through the open tricuspid valve into the right ventricle (the majority)
Backward - up the superior vena cava into the jugular veins (this is what you see as the a wave)

The backward pressure transmission is possible because there are no valves between the right atrium and the jugular veins.

How Measuring JVP Works

The sternal angle (angle of Louis, the manubriosternal junction) sits approximately 5 cm above the center of the right atrium regardless of patient position. So:

JVP (cmH₂O) = vertical height of jugular pulsation above the sternal angle + 5 cm

Normal JVP at 45° head-of-bed elevation is less than 3 cm above the sternal angle (i.e., total CVP less than 8 cmH₂O). The internal jugular is preferred over the external jugular because it connects more directly without valves. (Fuster and Hurst's The Heart, 15th Ed.)

Cannon A Waves - Why They Occur

You explained this correctly. Here's the precise mechanism:

Normal a wave: Atrium contracts → tricuspid valve is OPEN → most pressure goes forward into RV, a small pressure wave goes backward into the jugular veins → normal-sized a wave.

Cannon a wave: Atrium contracts → tricuspid valve is CLOSED (because the ventricle has already contracted and snapped it shut, or is contracting simultaneously) → there is NO forward exit → ALL the backward pressure has nowhere to go except retrograde into the jugular veins → giant cannon-shaped a wave.

This happens in:

Complete (3rd degree) AV block - complete dissociation of atria and ventricles means the atrium randomly contracts whenever it wants, sometimes right when the ventricle has just fired and the tricuspid is closed. These cannon waves are intermittent and irregular (because the dissociation is random).
Junctional/ventricular tachycardia with retrograde P waves - here the atrium contracts at the same time as the ventricle every beat → cannon waves are regular.
Ventricular pacing with AV dissociation
Premature ventricular contractions (PVCs) causing occasional cannon waves

As Fuster and Hurst's states: "Variable cannon a waves suggest the diagnosis of complete heart block in patients with new-onset bradycardia, and their occurrence in wide complex tachycardia is diagnostic of ventricular tachycardia rather than aberrancy."

Tricuspid Stenosis - Giant "a" Waves (Different Mechanism)

This is worth distinguishing from cannon waves. In tricuspid stenosis, the valve is narrowed but NOT closed - the atrium contracts against a stenotic (high-resistance) tricuspid, and must generate much higher pressure to push blood through. This also produces very large a waves - called giant a waves - but by a different mechanism (resistance, not obstruction). (Fuster and Hurst's)

Summary Table

Situation	a wave	Mechanism
Normal	Normal upstroke	RA contracts, some pressure goes back into jugular
Tricuspid stenosis	Giant a wave	RA contracts hard against narrow valve
Complete AV block	Irregular cannon a waves	RA randomly contracts against closed tricuspid
VT or junctional tach	Regular cannon a waves	RA + RV contract simultaneously every beat
Atrial fibrillation	Absent a wave	No organized atrial contraction
Pulmonary hypertension	Large a wave	RV diastolic dysfunction requires forceful atrial kick

To directly answer your final question: JVP reflects exclusively right atrial pressure because the internal jugular veins connect directly to the right atrium with no intervening valves. The left atrium's pressures cannot be assessed at the bedside this way - it requires indirect techniques (pulmonary wedge pressure or echo).

Why JVP Reflects Only Right Atrial Pressure (Not Left) The internal jugular veins drain directly into the superior vena cava, which empties into the right atrium. There are no valves between the internal jugular vein and the right atrium. This means the right atrium's pressure changes are transmitted directly and freely backward into the jugular veins - they act as a simple fluid column connected to the right atrium. The left atrium has no such direct connection to any visible superficial vein. Its pressures are assessed indirectly via the pulmonary capillary wedge pressure (a catheterization technique), or by echocardiography. So yes - JVP = right atrial pressure only. (Fuster and Hurst's The Heart, 15th Ed.) this as any ultra ultra short note

JVP = Right Atrial Pressure only

IJV → SVC → Right Atrium (no valves in between) = direct pressure transmission.

Left atrium has no such superficial venous connection - assessed only by PCWP or echo.

have a one small ultra short yield and I mean ultra short and high yield line stating that an increase in intrathoracic pressure as in this Valsalva maneuver or continuous positive airway ventilation will have a decrease in venous rhythm. And if you see on the other hand, for normal inspiration, we're gonna decrease the intrathoracic pressure because it's becoming more negative. So venous return will increase and hence P2 closure is delayed. That's the reason why the pulmonary valve usually closes a bit late. So that is the physiological splitting of S2 is more pronounced in case of inspiration.

Physiological S2 splitting widens on inspiration:

Inspiration → ↓ intrathoracic pressure → ↑ venous return to RV → RV takes longer to empty → P2 delayed → A2-P2 gap widens.

(Reverse: Valsalva/CPAP → ↑ intrathoracic pressure → ↓ venous return → splitting narrows.)

This is a shared conversation. Sign in to Orris to start your own chat.