Download Heart sounds: lub dub

JVP Waveform
Student Question
Why is there a steep x wave in the JVP in constrictive pericarditis? I can't manage to make sense in
my own head of this abnormality?
Reply
This is really a postgraduate topic and even postgraduates struggle to make sense of the
JVP. I’ll describe two important aspects of the cardiac cycle and relate these to the JVP. The
document on Diastolic Heart Failure may also be helpful. The jugular venous pulse (JVP)
reflects pressure changes in the superior vena cava and hence in the right atrium (RA).
Cardiac cycle
The heart starts contracting at the top and the contraction works its way down (sinus node,
AV node, bundle of Hiss etc), so that the atria contract just before the ventricles. This is
important for cardiac efficiency as this squeezes extra blood into the ventricles at the end of
ventricular diastole. It is lost in atrial fibrillation, which is why AF so often precipitates heart
failure.
Learning point: “Atrial systole occurs at the end of ventricular diastole”
This is sometimes referred to as the pre-systolic phase
This is when a 4th heart sound may occur (eg in heart failure) – an audible atrial contraction
Heart sounds: lub dub
Atrial systole
Rapid filling phase
lub
dub
ventricular systole
diastole
At the beginning of ventricular diastole, just after the second sound, blood rushes into the
ventricle- this is the rapid filling phase of diastole, sometimes referred to as the protodiastolic
phase. It is here that a third heart sound may sometimes be heard- blood rushing into a
failing ventricle which suddenly reaches its elastic limit and decelerates the incoming rush of
blood.
 Dr R Clarke
www.askdoctorclarke.com
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Normal JVP waveform
As the atria contract at the end of ventricular diastole, the A wave is created- a positive peak
at the end of ventricular diastole.
“a” wave
“c” wave
“v” wave
“y” descent
“x” descent
Ventricular
systole
As the atria relax, the pressure starts to fall and is sometimes interrupted by a small C wave,
due to the tricuspid vale bulging upwards into the atria right at the start of systole.
Then the pressure falls further, creating the x descent. This is the hard bit to understand.
The x descent is due to an increase in right atrial volume, with a fall in pressure, due to the
tricuspid valve being pulled downward during systole. This corresponds with a “systolic
surge” of blood from the SVC into the RA, with an increase in velocity in blood flow within
the vena cava. The ventricles may be ejecting, but the atria are relaxing and still filling up
with blood. (Atrial diastole occurs at least in part during ventricular systole.)
During ventricular systole, following the x descent, the pressure rises due to continuing
venous return to the atria, creating the V wave.
Early in diastole, due to the rapid phase of ventricular filling, the RA pressure falls rapidly,
creating the Y descent.
To remember this sequence, I hold on to two anchors: the A wave corresponding with atrial
contraction (pre-systolic) and the Y descent, corresponding with the rapid phase of
ventriuclar filling (protodiastolic). Between them, there is the X descent during ventricular
systole.
NB The x descent is replaced by a mirror image positive wave, (the CV wave) in tricuspid
regurgitation: the leaking valve allows direct transmission to the RA and JVP of the
ventricular systolic impulse. Regular systolic waves are seen (unlike canon waves which are
irregular, in complete heart block, when atria and ventricles occasionally happen to contract
at the same time).
 Dr R Clarke
www.askdoctorclarke.com
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Constrictive pericarditis
Different books give different accounts of this. Both X and Y descents way be prominent.
Y descent
Overall the JVP is raised and the mean RA pressure high.
Early in ventricular diastole blood rushes into the ventricle, driven by the high RA pressure,
so the normal Y descent is preserved and may be steeper than usual. However the
constriction means that the ventricle soon reaches its limited maximum volume, so no
further blood can enter and the RA pressure rises and is followed by a plateau phase during
mid-diastole. This Y descent followed by a plateau has been described as the “square root
sign”. Patients with constrictive pericarditis sometimes have a third heart sound; if prominent
this is described as a pericardial knock, due to this sudden and rapid incoming rush of blood
which stops suddenly in early diastole.
X descent
The JVP is raised and the mean RA pressure is high.
One of the reasons for the steep X descent is that the preceeding A wave is exaggerated,
reaching higher than normal pressures. At the end of diastole, the effect of the constriction is
most marked and when the atria contract, the RA pressure rises to its highest level, creating
the A wave.
After the A wave, there is then the usual systolic surge of blood into the atria, with a fall in
RA pressure as the tricuspid vale moves down, increasing RA volume. This may be the
main opportunity for RA filling as everything comes to a grinding halt in diastole due to the
constriction. For most of ventricular diastole, there has been a plateau phase in the atria,
with limited blood flow. So now during systole, blood flows into the atria; despite this the
pressure falls initially as atrial volume is increased by the descending tricuspid valve, which
is pulled down as “the roof of the ventricle” during ventricular systole. Then as blood
continues to flow into the atria, the pressure rises again, leading up to the V wave.
In summary, early diastolic filling is abnormally rapid, but no filling occurs during mid and
late diastole.
Cardiac Tamponade
The JVP is very high as there is fluid in the pericardial space impairing cardiac function
throughout the cycle. Venous return may be completely halted during diastole when cardiac
volume is maximal and hence intra-pericardial pressure is highest. This means that the Y
descent is usually abolished altogether.
Instead of its usually bimodal pattern, atrial filling is unimodal, occurring only during systole,
so the x descent (when the tricuspid valve falls during systole) may be the most prominent
part of the wave form. Often this is hard to detect as the JVP can be so high it is hard to
make out the wave form.
 Dr R Clarke
www.askdoctorclarke.com
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