The two main therapies consist of cardiac resynchronization therapy (CRT)
and implantable cardioverters/defibrillators (ICDs). CRT
began in response to the observation that cardiac dyssynchrony is
a common, but disadvantageous phenomenon in heart failure. In adults,
this is usually manifested electrocardiographically as a left bundle
branch block pattern, which results in late activation of the left
ventricular free wall. This late activation alters regional loading
conditions, myocardial blood flow and myocardial metabolism.60,61 There
are also regional alterations in gene expression and protein production
involved with mechanical function and stress. These alterations
ultimately lead to derangement of both contractile and noncontractile
elements, with the end result of ventricular remodeling, dilatation
and pump failure. Early studies with the use of CRT demonstrated
improvements in symptoms, quality of life, exercise capacity and
ejection fraction.62 More recently, CRT has been shown
to improve survival in adults with heart failure.63 The
definition of dyssnchrony has been evolving since the introduction
of this concept. CRT appears to have limited value in adults with heart
failure and a narrow QRS, despite the presence of mechanical dyssynchrony
by echocardiography.64,65 Interestingly, CRT may
also benefit papillary muscle function and thus mitral valve function
in patients with heart failure.66 The indications
and risk/benefit balance of CRT in children with heart
failure is not well defined. There have been reports of the use of
CRT acutely after surgery for congenital heart disease in children.67 There
have also been reports of successful use in children with congenital
heart disease more chronically.68 One large multicenter
retrospective report showed possible benefit in children with a
variety of heart diseases, although the indications and predictors
of beneficial effect are still not clear.69 Attempts
at using biventricular pacing to treat right bundle branch block
have been limited, but may have some benefit in selected children.70,71 The
use of CRT and/or ICDs in children is complicated by the small
size of children. In the very young, a thoracotomy is usually required.
Even in older children, these devices can be placed transvenously,
but growth can complicate the longevity of the leads, and using
the only supracardiac venous access can limit future needs for transvenous
access to the heart.
Death from heart failure can result from either end organ damage
from heart failure or from sudden death. Sudden death due to arrhythmias
is usually (but not always) due to ventricular tachycardia or fibrillation.
Implantable cardioverters/defibrillators (ICDs) can be used
as either secondary prevention or primary prevention. Secondary
prevention is used in those with previous cardiac arrest or documented
sustained ventricular tachycardia. ICDs are indicated in this group
of adults with heart failure, who also have a reasonable chance
of prolonged survival.
As with all other heart failure therapies, the indications for
the use of ICDs in children with heart failure are not well defined.
There have been descriptions of the successful use of ICDs in children,
although the complication rate (including inappropriate discharges)
is significant.72-74 In the very young (as stated above),
transvenous placement may not be an option, and the used of complex
subcutaneous arrays are being explored. Clearly, increased study
and experience is needed in the use of ICDs in children in order
to determine the indications and complications of this potentially
life-saving therapy.