curtis_2008.qxp 7/8/08 02:44 Page 77
Heart Block
Should Cardiac Resynchronization Therapy Be the Standard Treatment for
Patients with Atrioventricular Block Who Require Pacing?
a report by
Gustavo A Lopera, MD, FACC
1
and Anne B Curtis, MD, FHRS, FACC, FAHA
2
1. Assistant Professor of Medicine, and Director, Arrhythmia Service, Miami VA Healthcare System, University of Miami;
2. Professor of Medicine, Chief, Division of Cardiology, and Director, Cardiovascular Services, University of South Florida
Cardiac pacing remains the only effective treatment for patients with outcomes of ventricular dyssynchrony induced by RV pacing appear to be
symptomatic atrioventricular block (AVB). However, recent concern over the time-dependent and modulated by baseline LV systolic function, with an
detrimental effects of chronic right ventricular (RV) pacing has motivated earlier onset (months rather than several years) in patients with depressed
clinicians to look into the role of cardiac resynchronization therapy (CRT) in LV systolic function. Moreover, these adverse clinical outcomes have been
this group of patients. Chronic RV pacing causes ventricular dyssynchrony, associated with concomitant atrial and ventricular remodeling.
2,6,10–13
which may lead to atrial and ventricular remodeling, mitral regurgitation,
and diastolic and systolic dysfunction (see Figure 1).
1,2
Tolerance to chronic Results from observational studies and randomized clinical trials of CRT
RV pacing appears to be influenced by baseline left ventricular (LV) function, have consistently demonstrated significant improvements in clinical
the cumulative amount of ventricular pacing (VP), the duration of pacing, outcomes, reverse remodeling and survival in patients with New York
and other factors that are not currently understood. Heart Association (NYHA) class III and IV HF symptoms, LVEF ≤35%, and
a QRS interval duration >120ms.
14–18
These data suggest (but do not
Clinical Trials of Chronic Right Ventricular Pacing prove) that in patients with an indication for pacing therapy and in whom
Chronic RV pacing has been associated with a higher incidence of heart failure excessive RV pacing (>40% cum% VP) cannot be avoided, CRT could
(HF) and atrial fibrillation (AF) than atrial-based pacing modalities in randomized avoid or mitigate the detrimental effects of chronic RV pacing.
clinical trials.
3–10
In the MOST trial, the cumulative percentage of ventricular
pacing (cum% VP), rather than the specific pacing mode, was a strong predictor Clinical Trials of Cardiac Resynchronization Therapy in
of HF hospitalization and AF. A cum% VP >40% conferred a 2.6-fold increased Patients with Atrioventricular Block
risk for HF hospitalization in the dual-chamber (DDD) group compared with a In this group of patients, pacing therapy will necessarily lead to a chronic
lower percentage of pacing in similar patients. Similarly, the risk for AF was cum% VP >40%, which has been associated with a higher incidence of
increased by 1% for each 1% increase in cum% VP.
3,4
In a study by Andersen et
al., atrial pacing was associated with a significantly higher survival, less AF, less
HF, and fewer thromboembolic complications.
5
Fixed-rate single-chamber
Gustavo A Lopera, MD, FACC, is an Assistant Professor of
ventricular pacing (VVI) pacing was associated with a significant increase in LV Medicine and Director of the Arrhythmia Service at Miami VA
end systolic diameter and dilatation of the left atrium (LA).
6
These findings also
Healthcare System, the affilliated Teaching Hospital of the
University of Miami. His research focuses on risk stratification
appeared to be time-dependent, since there were no significant differences in
for sudden cardiac death, ablation of ventricular tachycardia,
mortality or HF during the initial three years of follow-up.
7
and cardiac pacing. Dr Lopera is a Fellow of the American
College of Cardiology (ACC) and a Member of the Heart
Rhythm Society (HRS). He graduated from Pontificia Bolivaria
The effects of ventricular dyssynchrony induced by RV pacing appear to
University School of Medicine in Medellin. He completed his
be more dramatic in patients with LV dysfunction or a previous history of training in internal medicine and cardiology at the University of Miami/Jackson Memorial
HF. In the Dual Chamber and VVI Implantable Defibrillator (DAVID) trial,
Hospital, and clinical cardiac electrophysiology training at the Brigham and Women’s
Hospital/Harvard Medical School.
in which all patients had an LV ejection fraction (EF) <40% at enrollment,
the primary combined end-point of hospitalization for HF or death was
significantly increased in the DDD group compared with the VVI-40 Anne B Curtis, MD, FHRS, FACC, FAHA, is a Professor of
group during a relatively short period of follow-up (mean eight
Medicine, Chief of the Division of Cardiology, and Director of
Cardiovascular Services at the University of South Florida in
months).
8,9
The worse outcome in the DDD group correlated with cum%
Tampa, Florida. She established the electrophysiology
VP >40%.
10
In the Multicenter Automatic Defibrillator Implantation Trial program at the University of Florida in 1986, and was
(MADIT) II, patients with cum% VP >50% had a significantly higher risk for
Director of Clinical Electrophysiology there until 2005. Dr
Curtis is prominently involved in a number of professional
HF and ventricular tachycardia (VT) or ventricular fibrillation (VF) requiring
organizations, and is a Past President of the Heart Rhythm
implantable cardioverter–defibrillator (ICD) therapy,
11
suggesting that Society (HRS). She took undergraduate training at Rutgers
ventricular dyssynchrony induced by RV pacing not only worsens HF, but
University in New Jersey and graduated from medical school at the Columbia University
College of Physicians and Surgeons in New York. Dr Curtis completed her medical residency at
could also be pro-arrhythmic.
Presbyterian Hospital in New York, and fellowships in cardiovascular diseases and clinical
cardiac electrophysiology at Duke University Medical Center.
In summary, data from randomized clinical trials have shown that >40%
E: acurtis@health.usf.edu
cum% VP is associated with a higher incidence of HF and AF. The adverse
© TOUCH BRIEFINGS 2008
77
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