498
U N I T 5
Circulatory Function
the kidneys. Angiotensin-converting enzyme inhibitors
have been shown to limit these harmful complications.
The
angiotensin II receptor blockers
appear to have
similar but more limited beneficial effects. They have the
advantage of not causing a cough, which is a trouble-
some side effect of the ACE inhibitors for many persons.
Aldosterone receptor antagonists
may be used in combi-
nation with other agents for persons with heart failure.
Hyperkalemia is a potential side effect of aldosterone
antagonism that requires additional monitoring.
1
β
-Adrenergic receptor blocking drugs
are used to
decrease left ventricular dysfunction associated with
activation of the sympathetic nervous system.
40
Large
clinical trials have shown that long-term therapy with
β
-adrenergic receptor blocking agents reduces morbid-
ity and mortality in persons with chronic heart failure.
The mechanism of this benefit remains unclear, but it
is likely that chronic elevation of catecholamines and
sympathetic nervous system activity causes progressive
myocardial damage, leading to a worsening of left ven-
tricular function and a poorer prognosis in persons with
heart failure.
Digitalis
has been a recognized treatment for heart
failure for over 200 years. The various forms of digi-
talis are called
cardiac glycosides.
They improve cardiac
function by increasing the force and strength of ventricu-
lar contractions. Digitalis and related cardiac glycosides
are inotropic agents that exert their effects by inhibiting
the Na
+
/K
+
-ATPase membrane pump, which increases
intracellular sodium; this in turn leads to an increase
in intracellular calcium through the Na
+
/Ca
+
exchange
pump
40
(see Fig. 20-1). The cardiac glycosides also
decrease sinoatrial node activity and decrease conduc-
tion through the atrioventricular node, thereby slowing
the heart rate and increasing diastolic filling time.
Vasodilator
agents such as isosorbide dinitrate and
hydralazine may be added to other standard medica-
tions for African-American patients with chronic heart
failure.
1
Agents such as nitroglycerin, nitroprusside, and
nesiritide (B-type natriuretic peptide) are used in AHFSs
to improve left heart performance by decreasing the pre-
load (through vasodilation) or reducing the afterload
(through arteriolar dilation), or both.
OxygenTherapy
Oxygen therapy increases the oxygen content of the
blood and is often used in patients with acute episodes
of heart failure. Noninvasive ventilation using continu-
ous positive airway pressure (CPAP) may be used to
relieve dyspnea, respiratory distress, and/or pulmonary
edema.
34
Continuous positive airway pressure by face
mask reduces the need for endotracheal intubation and
has minimal adverse effects or complications. Because
CPAP increases intrathoracic pressure, it also has the
potential for decreasing venous return and left ventricular
preload, thereby improving the cardiac ejection fraction
and stabilizing the hemodynamic status in persons with
severe heart failure.
40
Noninvasive ventilation can also be
provided by bilevel ventilation (BiPAP), which delivers
positive pressure during both inspiration and expiration.
AdvancedTherapies
Individuals with heart failure are at significant risk of
sudden cardiac death from ventricular fibrillation or
ventricular tachycardia. Implantation of a cardioverter–
defibrillator is indicated in selected patients with heart
failure to prevent sudden cardiac death.
1,2
A cardioverter–
defibrillator is a programmable implanted device that
monitors the cardiac rhythm. It has the capacity to pace
the heart and deliver electric shocks to terminate lethal
arrhythmias.
Refractory heart failure reflects deterioration in cardiac
function that is unresponsive to medical or surgical inter-
ventions. Since the early 1960s, significant progress has
been made in improving the efficacy of
ventricular assist
devices
(VADs), which are mechanical pumps used to
support ventricular function.
41
VADs are used to decrease
the workload of the myocardium while maintaining car-
diac output and systemic arterial pressure. This decreases
the workload on the ventricle and allows it to rest and
recover. Most VADs require an invasive open chest pro-
cedure for implantation. They may be used in patients
who fail or have difficulty being weaned from cardiopul-
monary bypass after cardiac surgery, those who develop
cardiogenic shock after myocardial infarction, those with
end-stage cardiomyopathy, and those who are awaiting
cardiac transplantation. Earlier and more aggressive use of
VADs as a bridge to transplantation and destination ther-
apy (permanent support) has been shown to increase sur-
vival.
41,42
Ventricular assist devices that allow the patient to
be mobile and managed at home are sometimes used for
long-term or permanent support for treatment of end-stage
heart failure, rather than simply as a bridge to transplanta-
tion. Ventricular assist devices can be used to support the
function of the left ventricle, right ventricle, or both.
42
Heart transplantation
is the preferred treatment for
many persons with end-stage cardiac failure and oth-
erwise good life expectancy.
1,2
Despite the overall suc-
cess of heart transplantation, donor availability remains
a key problem, and thousands are denied transplanta-
tion each year. Left ventricular remodeling is a surgi-
cal procedure designed to restore the size and shape of
the ventricle, and in a subset of patients with severe left
ventricular dysfunction this procedure may provide an
alternative to cardiac transplantation.
43
Heart Failure in the Elderly
Heart failure is one of the most common causes of dis-
ability in the elderly and is the most frequent hospital
discharge diagnosis for the elderly. Among the factors
that have contributed to the increased numbers of older
people with heart failure are the improved therapies for
ischemic and hypertensive heart disease.
44
Thus, persons
who would have died from acute myocardial disease
20 years ago are now surviving, but with residual heart
damage. Advances in treatment of other diseases have
also contributed indirectly to the rising prevalence of
heart failure in the older population. In contrast to
the etiology in middle-aged persons with heart failure,
