US_cardio_Spotnitz.qxp 23/7/08 04:32 Page 70
Heart Failure
The Surgeon’s Role in Resynchronization Therapy
a report by
Henry M Spotnitz, MD
1
and T Alexander Quinn, PhD
2
1. Department of Surgery; 2. Department of Biomedical Engineering, Columbia University, New York
Surgeons have contributed studies of the pathophysiology and treatment of early success of the Multicenter InSync Randomized Clinical Evaluation
arrhythmias in experimental animals and patients during thoracotomy. (MIRACLE) trial,
12
implantation of biventricular pacemakers and
This research has involved epicardial
1
and endocardial
2
pacemakers and pacemaker ICDs has expanded explosively. The worldwide market for
implantable cardioverter–defibrillators (ICDs).
3
Surgeons helped to define the resynchronization devices in 2007 is estimated to be in excess of 300,000
mechanisms and ablation methods for supraventricular arrhythmias (including implants annually, at a market value of more than $7 billion for devices
Wolff-Parkinson-White syndrome)
4
and for ventricular tachycardia associated alone. However, with an incidence of non-responders of 25–30%
13
(39%
with post-infarction, ventricular aneurysms,
5
and other conditions.
6
In in the MIRACLE trial
12
), roughly 90,000 of 300,000 recipients this year
congenital heart disease, techniques for mapping the conduction system were will not experience relief from symptoms of heart failure or functional
developed by surgeons and used to avoid heart block during surgical repair.
7
benefit. While patients may benefit from defibrillation capabilities in
Therapies for atrial fibrillation developed in the operating room include these implants, the healthcare community will pay more than $2 billion
atrioventricular node ablation
8
or modification
9
and the Cox-maze operation.
10
for ineffective resynchronization therapy. Why does resynchronization
Mapping and ablation technologies developed by surgeons have evolved to therapy fail, and how can surgical investigators help?
standard methods used in the electrophysiology lab.
Resynchronization therapy, developed for treatment of heart failure in dilated
However, the development of resynchronization therapy for heart failure cardiomyopathy,
12
partially reverses the effects of weakening and fibrosis of
has largely bypassed the surgical arena. The epicardial approach has been cardiac myocytes.
14
Clinical manifestations of myocyte dysfunction include a
marginalized as catheter technology has advanced and concern about left ventricular (LV) ejection fraction (EF) <35% and QRS interval above 120
the risks of general anesthesia and thoracotomy in patients with milliseconds. Left bundle branch block is common in this syndrome.
advanced heart failure has grown.
11
However, arguably, the minimization Segmental wall motion abnormalities and mitral regurgitation appear as heart
of surgical contributions to resynchronization therapy has left important failure progresses, reflecting the heterogeneity of electrical conduction
gaps in the understanding of how resynchronization therapy works, velocity and contractile function.
15
The hypothesis that simultaneous pacing of
where it should be applied, and how it can be optimized. Following the the septum and LV free wall could shorten the QRS complex, increase EF,
restore synchrony, and improve symptoms was confirmed clinically.
11–14
Resynchronization therapy has been associated with reduced mortality from
Henry M Spotnitz, MD, is the George H Humphreys, II, Professor
of Surgery at Columbia Univeristy. He has been a member of the
heart failure in some settings.
16
Resynchronization therapy also uniquely
Thoracic Surgery Attending Staff at New York Presbyterian since reduces myocardial oxygen consumption while improving function,
17
an ideal
1975. He was previously a Staff Associate at the National Heart
combination previously characteristic only of mechanical assistance devices.
Institute (NHI). His R01 grants (1978–2006) involved the study
of the effects of cardiac surgery on heart function. Professor
Spotnitz’s research interests include myocardial protection in Most resynchronization therapy is performed with endocardial lead insertion
congenital heart disease, pacemaker implants in children, and
under local anesthesia using a limited choice of ventricular pacing sites.
biventricular pacing for acute heart failure. His research is
supported by grants from the American Heart Association (AHA)
Generally, the septum is paced with a conventional lead from the RV apex.
and the National Institutes of Health (NIH), among others. He The LV free wall is paced with a small cross-section lead from a ventricular
received a BA from Harvard and later gained an MD.
branch of the coronary sinus. Inability to enter the os of the coronary sinus
E: hms2@columbia.edu or to find an appropriate, stable location for coronary sinus pacing causes
T Alexander Quinn, PhD, is a Research Assistant at Columbia
failure of implant procedures in 5–10% of candidates.
10,12
Furthermore, the
University. He is experienced with response surface analysis of locations of coronary sinus branches, the tapering cross-section of those
complex data sets and hybrid computer development for the
branches, and limitations of current technology reduce the number of usable
automated pacing and detection of compliance abnormalities. He
was a Moderated Poster Presentation Award winner at the
pacing sites in any given patient.
18
The ability to objectively compare small
American Society for Artificial Internal Organs (ASAIO) 50th hemodynamic effects of pacing from different sites is limited by the time
Anniversary Conference and a Finalist (second place) in the PhD
required to reposition the LV lead, optimally requiring multisite electrodes.
Student Paper Competition at the American Society of Mechanical
Engineers (ASME) Summer Bioengineering Conference. Mr Quinn
Despite these difficulties, available data indicate that the location of the LV
received a BSci in physiology and physics from McGill and an MS free wall lead is an important determinant of the efficacy of resynchronization
and PhD in biomedical engineering from Columbia University.
therapy. Lateral and inferior LV lead locations have been utilized empirically.
18
In dilated cardiomyopathy, it has been suggested that the LV lead should be
70 © TOUCH BRIEFINGS 2008
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