Valvular regurgitation
is defined as the presence of backwards, or retrograde, flow across
a given closed cardiac valve. It should be realized by beginners
that the terms "regurgitation" and "insufficiency" are synonyms
and may be used interchangeably.
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| Fig.2.1 |
It is assumed that there is normally no flow backwards into the
ventricles through the aortic or pulmonic valves in diastole. Similarly,
there is no flow backwards into the atria across the mitral or tricuspid
valves in systole. Thus, the first effect of regurgitation on blood
flow through the heart is a change in direction. Figure 2.1 demonstrates
the abnormal direction of flow in the left heart for mitral and
aortic regurgitation in systole and diastole respectively. Given
the ability of Doppler echocardiography to detect the direction
of blood flow, it is seems ideally suited for assessment of valvular
insufficiencies.
The second effect of regurgitation on cardiac blood flow is the
creation of turbulence. Most valvular regurgitation is associated
with some abnormality of leaflet coaptation. Regurgitant jets originate
from small, irregular openings. They may be directed quite eccentrically
and they are almost always turbulent. Regurgitant jets are made
up of many different velocities and complex flow patterns. These
features are represented on the Doppler recording as spectral broadening,
which is the graphic equivalent of turbulent flow.
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| Fig.2.2 |
The third factor that characterizes the abnormal flow of a regurgitant
jet is an increase in velocity, which is a result of a pressure
gradient that exists across a regurgitant valve. For example, normal
systolic pressure in the left ventricle is over 100 mmHg. At the
same time, the pressure in the left atrium is very low and ranges
from 2 to 12 mmHg. The left panel of Figure 2.2 demonstrates these
normal pressure relationships. Even though the pressure differences
are great, no communication exists between the two chambers and
no retrograde (or backwards) flow.
When mitral regurgitation is present, however, the abnormal communication
between the left ventricle and left atrium in systole, and a pressure
difference (or gradient) exists (Fig. 2.2, right panel). When the
pressures within both the left atrium and ventricle are within normal
ranges a gradient of 85 mmHg or more exists and produces retrograde
flow into the left atrium. This flow takes the form of a high velocity
regurgitant jet, as predicted by the Bernoulli equation described
in detail in Unit 1.
As mitral insufficiency becomes worse and leads to chronic elevation
of left atrial pressure, the systolic gradient between the left
ventricle and the left atrium is reduced. In these cases, left atrial
pressure may rise to very high levels.
2004