Biomedical Engineering Reference
In-Depth Information
All patients underwent surgical revascularization; in addition,
one group was randomly assigned to ICD implantation.
During the follow-up period, no difference in all-cause mor-
tality was found between the ICD group and that without
ICD. During the follow-up period, cumulative mortality from
arrhythmic death was 6.9 % and all-cause mortality was
21.1 % in the control group; in the ICD group, cumulative
mortality from sudden death was 4.0 % and all-cause mortal-
ity was 22.8 %. Treatment with ICD implantation had no
impact on all-cause mortality.
number of cardiovascular diseases. This dysfunction can
be systolic, diastolic, or both. The leading cause of chronic
systolic heart failure is ischemic heart disease, usually a con-
dition that occurs after suffering a myocardial infarction. The
second leading cause is dilated cardiomyopathy. The other
causes are less frequent.
The guidelines suggest sufficient demonstration of the
clinical efficacy of CRT from large, randomized studies of
patients with a widened QRS complex (
120 ms). In most
patients, this disorder is accompanied by a dyssynchrony of
mechanical contraction that can be improved by using CRT.
Currently, there is no evidence supporting this indication in
patients with heart failure and a QRS width < 120 ms.
Similarly, no evidence exists that it would be possible to
improve the long-term efficacy of CRT by selecting patients
based on echocardiographic assessment or another diagnos-
tic method. Indications for CRT-P and CRT-D implantations
overlap to a certain degree. The most recent guidelines on
SCD emphasize that, when indicating CRT-D as part of pri-
mary prevention, it is necessary to take into account the
patient's expected survival. These guidelines state explicitly
that the use of ICD for the purpose of primary prevention is
indicated in patients with heart failure with severe LV dys-
function regardless of the underlying disease and in whom
survival rates longer than 1 year can be expected.
According to actual ACC/AHA/HRS 2008 Guidelines for
Device-Based Therapy of Cardiac Rhythm Abnormalities
[34, 35], the indications (class I and class IIa) for CRT are
described in the following paragraphs.
In instances of an LVEF
³
6.3
Indications for Cardiac
Resynchronization Therapy
CRT-D and CRT-P function are indicated in patients with
moderate to severe heart failure (NYHA class III/IV) in
whom symptoms persist despite stable optimal pharmaco-
logical therapy and who remain with an LVEF
£
35 % and a
QRS width
120 ms [ 44 ] . The stages of heart failure are
described in Table
6.4
.
There is no universally accepted definition of heart fail-
ure. The most common definition is a hemodynamic one.
The term
chronic heart failure
thus refers to a number of
symptoms that are caused by impairment of the heart's work
when, in spite of sufficient ventricular filling, cardiac output
drops and the heart is unable to meet the metabolic needs of
tissue. To establish the diagnosis of chronic heart failure,
symptoms must be present and impaired cardiac function
must be demonstrated objectively. Heart failure is a syn-
drome, not a definite diagnosis.
The term
compensated heart failure
refers to a condition
in which there has been a resolution of clinical signs and
symptoms of heart failure because of compensatory mecha-
nisms or treatment. The term
asymptomatic dysfunction
refers to a condition in which there is reduced systolic and/or
diastolic LV function but the patient is without either treat-
ment or symptoms. Chronic heart failure develops as a result
of dysfunction of the ventricular myocardium, arising in a
³
•
0.12 s,
and sinus rhythm, CRT with or without an ICD is indi-
cated for the treatment of NYHA functional class III or
ambulatory class IV heart failure symptoms with optimal
recommended medical therapy.
In instances of an LVEF
£
35 %, a QRS duration
³
•
0.12 s,
and atrial fibrillation, CRT with or without an ICD is rea-
sonable for the treatment of NYHA functional class III or
ambulatory class IV heart failure symptoms with optimal
recommended medical therapy.
£
35 %, a QRS duration
³
Table 6.4
New York Heart Association classi fi cation of stages of heart failure [
44 ]
NYHA class
De fi nition
Examples
I (Mild)
No limitation of physical activity. Ordinary physical
activity does not cause undue fatigue, dyspnea, or
palpitations
Carry 11 kg up eight steps; carry objects weighing 36 kg; shovel
snow spade soil; ski; play squash, handball, or basketball; jog or
walk 8 km/h
Slight limitation of physical activity. Comfortable at rest,
but ordinary physical activity causes fatigue, dyspnea,
palpitations, or angina
Sexual intercourse without stopping; garden; roller skate; walk
7 km/h on level ground; climb one flight stairs at a normal pace
without symptoms
II (Mild)
III (Moderate)
Moderate limitations of physical activity. Comfortable at
rest; less than ordinary physical activity causes fatigue,
dyspnea, palpitations, or angina
Shower or dress without stopping; strip and make a bed; clean
windows; play golf; walk 4 km/h
Severe limitation of physical activity. Symptoms occur at
rest; any physical activity increases discomfort
Cannot do any of the above activities
IV (Severe)
