C h a p t e r 2 0
Heart Failure and Circulatory Shock
489
In heart failure with a reduced ejection fraction, a
decrease in cardiac output and renal blood flow leads
to increased sodium and water retention by the kidney
with a resultant increase in vascular volume and venous
return to the heart, and an increase in ventricular end-
diastolic volume. Within limits, as preload and ventric-
ular end-diastolic volume increase, there is a resultant
increase in cardiac output. Although this may preserve
the resting cardiac output, the resulting chronic eleva-
tion of left ventricular end-diastolic pressure is transmit-
ted to the atria and the pulmonary circulation, causing
pulmonary congestion.
An increase in cardiac muscle stretch, as occurs
with the Frank-Starling mechanism, also produces an
increase in ventricular wall tension with a resultant
increase in myocardial oxygen consumption. Because
increased wall tension increases myocardial oxygen
requirements, it can produce ischemia and contribute
to further impairment of cardiac function. The use of
diuretics in persons with heart failure helps to reduce
vascular volume and ventricular filling, thereby unload-
ing the heart and reducing ventricular wall tension.
Sympathetic Nervous System
Stimulation of the sympathetic nervous system plays
an important role in the compensatory response to
decreased cardiac output and in the pathogenesis of
Vascular resistance
(afterload)
Cardiac contractility
Heart rate
Sympathetic
reflexes
Vascular
tone
Frank-Starling
mechanism
Myocardial
hypertrophy and
remodeling
Renal blood flow
Vascular volume
Sodium and
water retention
Angiotensin II
Renin-
angiotensin-
aldosterone
mechanism
Adrenal
gland
Venous return
(preload)
Aldosterone
Cardiac
output
FIGURE 20-2.
Compensatory
mechanisms in heart failure.
The Frank-Starling mechanism,
sympathetic reflexes, renin-
angiotensin-aldosterone mechanism,
and myocardial hypertrophy function
in maintaining cardiac output for the
failing heart.
Cardiac output (L/min)
5
Left ventricular end-diastolic pressure (mm Hg)
12
22
A
B
C
D
FIGURE 20-3.
Left ventricular length-tension (Frank-Starling)
function curves. Curve A: Normal function curve, with a normal
cardiac output and optimal left ventricular end-diastolic (LVED)
filling pressure. Curve B: Compensated heart failure with
normal cardiac output at higher LVED pressures. Curve C:
Decompensated heart failure with a decrease in cardiac output
and elevated LVED pressures, with eventual elevation of
pulmonary capillary pressure and development of pulmonary
congestion. Curve D: Cardiogenic shock, with an extreme
decrease in cardiac output and marked increase in LVED
pressures.
