(Circulation. 2000;101:40.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Cardiovascular Research Institute and Department of Medicine, University of California, and the Section of Cardiology, Department of Veterans Affairs Medical Center, San Francisco, Calif (J.R.T., B.M.M.); the Biostatistics Center, University of Wisconsin, Madison, Wis (M.J., S.A.); Division of Cardiology, Mt Sinai Medical Center, New York, NY (M.L.K.); Section of Cardiology, Department of Veterans Affairs Medical Center, Dallas, Tex (E.J.E.); Cardiology Division, The Cleveland Clinic Foundation, Cleveland, Ohio (G.F.); and Cardiology Division, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, NY (M.P.)
Correspondence to Barry M. Massie, MD, Section of Cardiology (111C), San Francisco Veterans Affairs Medical Center, 4150 Clement St, San Francisco, CA 94121.
| Abstract |
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Methods and ResultsVentricular arrhythmias
were analyzed and quantified by use of prespecified criteria on
baseline ambulatory ECGs from 1080 patients with New York Heart
Association (NYHA) class III/IV symptoms and a left
ventricular ejection fraction
35% enrolled in PROMISE.
The relationship of ventricular arrhythmias and
other clinical parameters to overall mortality and sudden
death classified by an independent, blinded mortality committee was
determined. There were 290 deaths, of which 139 were classified as
sudden. Of the several measures of ventricular ectopy that
were univariate predictors, the frequency of nonsustained
ventricular tachycardia (NSVT) was the most
powerful predictor and remained a significant independent predictor
when included with other clinical variables in
multivariate models of both sudden death mortality and
nonsudden death mortality. However, multiple logistic
analysis with models including the clinical variables with
and without the NSVT variable demonstrated that the frequency of
NSVT did not add significant information beyond the clinical
variables.
ConclusionsThis study demonstrates that ventricular arrhythmias do not specifically predict sudden death in patients with moderate-to-severe heart failure. Thus, the finding of asymptomatic NSVT on ambulatory ECG does not identify specific candidates for antiarrhythmic or device therapy.
Key Words: arrhythmia death, sudden heart failure inotropic agents prognosis
| Introduction |
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Several recent studies1 2 3 4 5 have suggested that ventricular arrhythmias detected by ambulatory electrocardiography (AECG) may identify patients at high risk for sudden death. However, these studies have a number of limitations, including post hoc hypotheses, retrospective analyses, AECGs in only a subset of patients, small sample size and number of events, and lack of predesignated criteria for mechanism of death and interpretation of arrhythmias. Thus, several critical questions remain unresolved: Do the presence or characteristics of baseline ventricular arrhythmias specifically identify patients at high risk for sudden death? Do they provide additional prognostic information beyond that of readily available clinical variables? Can these ventricular arrhythmias guide selection of therapeutic interventions directed against reducing sudden death?
These questions have assumed new importance with the evolving role of implantable cardioverter defibrillators (ICDs) as an approach to preventing sudden death,6 although not without significant cost and morbidity.7 Thus, it has become increasingly important to identify patients at high risk for sudden arrhythmic death. AECG monitoring has the potential to fulfill this role by detecting and quantifying the nature, frequency, and duration of ventricular arrhythmias, but in the absence of evidence that these arrhythmias are specific predictors of outcomes or that they can guide therapy, current guidelines discourage the use of this procedure.8 9
The present study was undertaken to determine whether ventricular arrhythmias were independent and specific predictors of sudden death with data from the Prospective Randomized Milrinone Survival Evaluation (PROMISE).10 PROMISE enrolled 1088 high-risk CHF patients, all of whom underwent 24-hour baseline AECG, and of the 290 deaths during follow-up, 139 were classified as sudden by an end-point committee, thus providing the largest cohort to date of CHF patients who experienced sudden death after AECG monitoring. The goal of the present study was to provide information for the practicing clinician on the significance of ventricular arrhythmias in patients with CHF.
| Methods |
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Patient Population
The inclusion and exclusion criteria for PROMISE have been
described elsewhere10 and required that patients have New
York Heart Association (NYHA) class III or IV symptoms for
3 months
and a left ventricular ejection fraction
35% as measured
by radionuclide ventriculography. All patients were required to be
receiving treatment with a diuretic, an ACE
inhibitor, and digoxin. The protocol was approved by the
institutional review boards at all participating centers, and patients
gave informed written consent before they entered the study.
AECG Monitoring
The 24-hour AECG recordings were obtained within 7 days
before randomization. The tapes were scanned and analyzed by
experienced technicians and overread by supervisors at an independent
laboratory (Clinical Data, Inc, Boston, Mass), and 10% of the
recordings were validated by an independent cardiologist. The
results were not available to the treating physician. The total number
of ventricular ectopic beats and the numbers of single
ventricular ectopic beats, paired ventricular
beats, and ventricular tachycardia events
(defined as
3 consecutive ventricular ectopic beats with
mean R-to-R cycle length <600 ms) were determined. Several
prospectively defined qualitative (ie, presence or absence) and
quantitative indices of ventricular ectopy were derived
from the AECG and examined as predictors of outcome.
Outcome Definitions and Determination
The primary end point of the study was mortality due to all
causes. The mode of death was reviewed in a prospectively defined,
blinded fashion by a mortality committee and classified as sudden or
nonsudden. Sudden death was defined as an unexpected circulatory
collapse resulting in death within 1 hour in a previously clinically
stable patient.
Data Analysis and Statistical Methods
The baseline characteristics of the treatment groups were
compared by the t statistic for continuous
variables and by the
2 statistic for
noncontinuous variables. To test the hypothesis that ambulatory
ventricular ectopy is predictive of outcome in patients
with CHF, a number of prespecified analyses were performed,
including a
2 analysis of selected
dichotomous AECG variables. Univariate and
multivariate Cox proportional hazards analyses
were then used on selected AECG and clinical variables. Because of
the nonnormal distribution of some continuous AECG variables, a
logarithmic transformation was performed on the number of
ventricular ectopic beats per hour, the number of episodes
of nonsustained ventricular tachycardia (NSVT),
and the number of successive beats of NSVT. The AECG variable with
the greatest predictive power was analyzed in a logistic
survival model with sensitivity and specificity analyses. In
addition, 2 multivariate logistic models were then
developed that used the clinical variables with and without the
most powerful AECG variable to assess the incremental additive
information from this variable. Sensitivity and specificity
analyses were performed on both of these models, and receiver
operating characteristic (ROC) curves were generated. Analyses
were performed with the SAS statistics package (version 6.12). Results
of analyses were considered significant at a level of
P<0.05.
| Results |
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AECG Variables Are Univariate Predictors of Overall
Mortality and Sudden Death
Two hundred ninety (27%) patients died, of whom 139 (13%) were
classified as sudden deaths, representing 48% of the total
deaths that occurred during the trial. Frequent premature
ventricular contractions (PVCs; >30/h), NSVT, and NSVT of
>10 beats duration identified groups with 55%, 68%, and 60%
increased all-cause mortality, respectively (Table 2
). Clinical predictors also defined
groups at significantly increased risk of all-cause mortality.
|
Frequent PVCs (>30/h), the presence of couplets, and the
presence and frequency (>5 episodes) of NSVT each defined groups with
an
50% increased risk of sudden death. Age, NYHA class, and
ejection fraction also defined groups at significantly increased risk
of sudden death (42%, 70%, and 78%, respectively). The presence of
coronary artery disease was not a significant predictor of
sudden death. Milrinone treatment was associated with a 60% increase
in sudden death in this analysis.
Univariate Cox proportional hazards models
demonstrated that many clinical and AECG variables predicted
overall mortality (Figure 1A
), sudden
death (Figure 1B
), and nonsudden death mortality. All of the
AECG variables were significant predictors of overall mortality and
sudden death. These variables were also significant predictors of
nonsudden death mortality, which indicates their nonspecificity for
mode of death.
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Multivariate Predictors of All-Cause Mortality and
Sudden Death
Multivariate general linear proportional hazards
models were used to identify independent predictors of mortality while
controlling for the effects of the other variables. Important
clinical variables (age, NYHA class, presence of coronary
artery disease, ejection fraction, systolic blood pressure, and
PROMISE treatment arm) that were significant univariate
predictors were entered into separate models for all patients and each
separate treatment arm (placebo and milrinone). Antiarrhythmic drug
therapies (all antiarrhythmics, amiodarone, and other
antiarrhythmics) were not significant univariate predictors
of any form of mortality, nor did they alter the
multivariate models; consequently, they were not
included in any further analyses. These analyses
demonstrated that all of the selected clinical variables were
significant independent predictors of overall mortality and that
ejection fraction was the most powerful clinical predictor of sudden
death (Table 3
). The relative risks in
the analysis of the placebo group alone were almost identical
to those of the combined group, which suggests that milrinone was not
responsible for these results. The one exception was NYHA class, for
which an interaction effect with milrinone was noted: NYHA class IV
patients had greater excess mortality with milrinone than did class III
patients.
|
Because the main purpose of this study was to assess the additional
predictive value of ventricular arrhythmias in the
context of important clinical variables, the AECG variables
were included in multivariate models with the clinical
variables. When the variables of frequency of PVCs (ln PVC/h),
presence of NSVT, frequency of NSVT (ln NSVT episodes), and duration of
longest run of NSVT (ln NSVT beats) were added individually to the 6
clinical variables, each was a significant independent predictor of
both overall mortality and sudden death, with the frequency of NSVT
being the most powerful. An additional analysis was performed
with both a forward and backward elimination procedure in a
multivariate Cox proportional hazards model that
included all of the clinical variables and the 4 AECG
variables; these analyses converged on the same
variable set, and the results of the backward elimination procedure
are shown in Table 4
. The number of NSVT
episodes was a significant predictor of overall mortality, sudden
death, and nonsudden death mortality and was the most powerful
predictor of sudden death. These analyses support the
hypothesis that AECG variables, especially the frequency of NSVT
episodes, are significant independent predictors of sudden death,
nonsudden death mortality, and overall mortality.
|
Ventricular Arrhythmias Are Not Specific
Predictors of Sudden Death
Although it is clear that AECG variables are significant
predictors of sudden death in patients with CHF, the sensitivity and
specificity of these findings are the clinically relevant issue. To
address this issue, the best of the AECG variables (ln NSVT
episodes) was entered into a univariate logistic
analysis, which yielded false-positive rates of >80% at all
sensitivity levels of
50% for predicting sudden death. The ROC curve
(Figure 2
) demonstrates that this
variable has poor sensitivity and specificity, because it did not
discriminate between sudden death and all-cause mortality.
|
Multivariate logistic regression models were developed
to further investigate the ability of AECG variables to
specifically predict sudden death. A logistic model was developed that
included only the clinical variables, and this model was a very
significant predictor of sudden death (Wald
2
46.6; P<0.0001), with 67% of the observed responses
concordant with the model. However, at sensitivity levels >50%, there
was a >80% false-positive rate. When the number of NSVT episodes was
added to the model, it remained significant (Wald
2 58.4; P<0.0001), although as
discussed above, only 69% of the observed results were concordant with
the model, and there were similarly high false-positive rates. The
addition of the strongest AECG predictor did not provide significant
incremental prognostic information, as demonstrated by analyses
that included either all patients or the placebo group alone (Figure 3
, respectively). Not only were both
models associated with poor sensitivity and specificity, but the ROC
curves of the 2 models were essentially superimposable.
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| Discussion |
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Previous studies have suggested that ventricular arrhythmias are statistically significant independent predictors of mortality, and the results of the present study support this observation. All of the selected AECG variables were significant predictors of both sudden death and overall mortality in univariate analyses, as well as in multivariate models that included the clinical variables of age, NYHA functional class, presence of coronary artery disease, ejection fraction, and systolic blood pressure. Of these AECG variables, the frequency of NSVT episodes was the most powerful predictor of sudden death, nonsudden death mortality, and overall mortality. Other studies have demonstrated the ability of AECG variables to predict both overall mortality and sudden death. These studies showed that the duration,4 frequency,2 or presence3 5 of NSVT, the presence of couplets,1 5 and the frequency of PVCs1 predicted sudden death.
Two recent studies (GESICA [Gruppo de Estudio de la Sobrevida en la
Insuficiencia Cardiaca en Argentina] and CHF-STAT [Congestive Heart
FailureSurvival Trial of Antiarrhythmic Therapy]) have addressed
similar issues, although with fewer patients and less rigorous
methodology. In the GESICA trial,5 24-hour AECGs from 295
patients with advanced CHF were analyzed. There were 123 deaths
in this subgroup, 44 of which were classified as sudden. Patients with
NSVT were found to have significantly worse CHF, a higher overall
mortality, and a greater incidence of sudden death. When a post hoc
combined dichotomous variable of couplets and/or NSVT was used,
there was an 89% sensitivity and a 42% specificity for the prediction
of sudden death, with a 21% positive predictive value. Although these
results indicate that ventricular arrhythmias are a
marker for poor ventricular function and more severe CHF,
the lack of multivariate analyses does not
permit assessment of whether arrhythmias are independently
useful in predicting sudden death. Furthermore, the GESICA patient
population was unusual in that >60% of patients had
nonischemic cardiomyopathy (9.3% due to
Chagas disease), and patients with asymptomatic
ventricular tachycardia of
10 beats were
excluded.
The present study included >3 times as many patients with AECGs
and sudden death events, had prospectively defined criteria for
ventricular arrhythmias, classified deaths via
predefined criteria by an independent mortality committee, and
incorporated clinical factors known to affect mortality in
multivariate models for sudden death, nonsudden death
mortality, and overall mortality. The results of this study demonstrate
clearly that ventricular arrhythmias are
nonspecific predictors of mortality, as intuitively shown by the
frequency of NSVT episodes as a powerful predictor of both sudden death
and nonsudden death mortality. Furthermore, as demonstrated in Figure 3
, the addition of the frequency of NSVT episodes to the
multivariate model with clinical variables did not
significantly improve the sensitivity or specificity of the model for
sudden death, which suggests that it had limited additional prognostic
information.
The CHF-STAT study11 enrolled 674 patients with symptoms
of CHF, cardiac enlargement,
10 PVCs per hour, and ejection fraction
40% in a trial of amiodarone versus placebo. These patients
were selected for an increased baseline arrhythmia and had a
mean PVC frequency of >250 per hour. In this selected group, there was
an 80% incidence of NSVT, the presence of which was a
univariate predictor of sudden death. However, in
multivariate models, only ejection fraction was a
significant predictor of sudden death. Thus, these findings lead to a
similar conclusion that NSVT does not predict a higher risk of sudden
death.
The results of the present study suggest that AECG monitoring does
not select patients at high risk for sudden death, but they neither
contradict nor confirm the findings of the recent MADIT6
trial (Multicenter Automatic Defibrillator Implantation Trial). MADIT
suggested that a highly selected group of patients (previous myocardial
infarction, left ventricular ejection fraction
35%,
documented asymptomatic NSVT, and inducible,
nonsuppressible ventricular tachycardia on
electrophysiological study) treated with
ICDs have improved survival.
Three points seem to be most relevant to placing these trials in perspective. First, the role of the AECG is different in the 2 trials. In MADIT, the AECG results were the starting point for additional evaluation and selection of patients (eg, electrophysiological study), whereas our analysis only interprets the direct relationship of AECG variables to sudden death. It may be that electrophysiological study results would provide a more specific indicator of sudden death, although this hypothesis was not tested in either trial. Unfortunately, the MADIT investigators report that there was no information on the number of patients screened for enrollment in the trials and no follow-up of the excluded patients. Second, MADIT was not designed to investigate the prognostic value of the screening algorithm that was used, but rather addressed the question of whether automated ICD therapy would be beneficial in a highly selected group of patients. There was no attempt by the study design to determine that the screening algorithm selected the group of patients who would receive the greatest benefit or that other groups who did not meet the inclusion criteria would also benefit. All we can conclude is that AECG is not a very efficient approach to screening for sudden death candidates in the PROMISE population. Third, the patient populations are quite different. All of the MADIT patients had coronary artery disease (versus 54% of the PROMISE patients), which made this group more likely to have inducible ventricular tachycardia on electrophysiological study, and relatively few had CHF of the severity required in PROMISE (65% of the patients were NYHA class II/III in MADIT compared with 58% and 42% with NYHA class III or IV, respectively, in PROMISE). Thus, regardless of whether one accepts the MADIT results, based on the results of the present study, AECGs alone provided no specific prognostic information in the patients studied in PROMISE.
Although the findings of the present study are compelling, there
are several limitations. First, the possible confounding influence of
the inclusion of patients randomized to milrinone treatment must be
considered. To address this issue, multivariate
statistical models designed to control for the effect of milrinone were
selected. Furthermore, separate analyses with the smaller
placebo group confirmed the findings of the combined group, although
with reduced power. Second, this study was limited only to AECG
variables and did not include QT dispersion, heart rate variability
or late potentials. Although each of these may hold some
promise, they have yet to be shown to add predictive information beyond
that of AECG and clinical variables. Third, other mechanisms for
sudden death, such as bradycardia and electromechanical dissociation,
may dilute the ability of ventricular arrhythmia
variables to predict sudden death in this
population.12 13 However, there are few data to suggest
that the AECG would provide useful predictive information for these
forms of sudden death either. Fourth, caution must be exercised in the
application of these findings. The patients in PROMISE (NYHA class
III/IV with left ventricular ejection fraction
35%) were
a selected sample of the overall CHF population, and these results may
not be generalizable. It is possible that ventricular
arrhythmias may be more specific predictors in patients with
less severe CHF, although this was not the case in CHF-STAT, in which
>50% were NYHA II.11 Finally, the classification of
death in CHF trials is always difficult14 15 16 17 because of
individual variation in interpretation and multiple possible
mechanisms. The PROMISE trial had a central mortality committee, which
provided internally consistent, although still potentially
inaccurate, classification.
The results of the present study provide important answers to the questions confronting practicing clinicians. The presence or nature of baseline ventricular arrhythmias in patients with moderate-to-severe CHF does not specifically define a group at high risk for sudden death and does not provide additional prognostic information beyond readily available clinical variables. Therefore, the clinician should avoid the understandable temptation to perform AECG in CHF patients without symptoms of arrhythmia, even in those known to have frequent ectopy. Until the results of other trials that refute these findings are available, the presence of asymptomatic NSVT should not guide therapeutic interventions, such as the institution of antiarrhythmic therapy or implantation of antifibrillatory devices.
| Acknowledgments |
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| Footnotes |
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Received February 26, 1999; revision received August 4, 1999; accepted August 5, 1999.
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M T Kearney, K A A Fox, A J Lee, W P Brooksby, A M Shah, A Flapan, R J Prescott, R Andrews, P D Batin, D L Eckberg, et al. Predicting sudden death in patients with mild to moderate chronic heart failure Heart, October 1, 2004; 90(10): 1137 - 1143. [Abstract] [Full Text] [PDF] |
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H. J.J. Wellens Cardiac arrhythmias: The quest for a cure: A historical perspective J. Am. Coll. Cardiol., September 15, 2004; 44(6): 1155 - 1163. [Abstract] [Full Text] [PDF] |
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J. O. O'Neill, J. B. Young, C. E. Pothier, and M. S. Lauer Severe frequent ventricular ectopy after exercise as a predictor of death in patients with heart failure J. Am. Coll. Cardiol., August 18, 2004; 44(4): 820 - 826. [Abstract] [Full Text] [PDF] |
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E. Paoletti, C. Specchia, G. Di Maio, D. Bellino, B. Damasio, P. Cassottana, and G. Cannella The worsening of left ventricular hypertrophy is the strongest predictor of sudden cardiac death in haemodialysis patients: a 10 year survey Nephrol. Dial. Transplant., July 1, 2004; 19(7): 1829 - 1834. [Abstract] [Full Text] [PDF] |
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H Weber, K Allikmets, and G Kornfeld Treating electrical instability in sudden cardiac death survivors - are we looking at the right side of the coin? Eur. Heart J., April 2, 2004; 25(8): 623 - 625. [Full Text] [PDF] |
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M. J Janse Electrophysiological changes in heart failure and their relationship to arrhythmogenesis Cardiovasc Res, February 1, 2004; 61(2): 208 - 217. [Abstract] [Full Text] [PDF] |
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W. G. Stevenson and L. M. Epstein Predicting Sudden Death Risk for Heart Failure Patients in the Implantable Cardioverter-Defibrillator Age Circulation, February 4, 2003; 107(4): 514 - 516. [Full Text] [PDF] |
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M. T. Kearney, K. A. A. Fox, A. J. Lee, R. J. Prescott, A. M. Shah, P. D. Batin, W. Baig, S. Lindsay, T. S. Callahan, W. E. Shell, et al. Predicting death due to progressive heart failure in patients with mild-to-moderate chronic heart failure J. Am. Coll. Cardiol., November 20, 2002; 40(10): 1801 - 1808. [Abstract] [Full Text] [PDF] |
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R. Berger, M. Huelsman, K. Strecker, A. Bojic, P. Moser, B. Stanek, and R. Pacher B-Type Natriuretic Peptide Predicts Sudden Death in Patients With Chronic Heart Failure Circulation, May 21, 2002; 105(20): 2392 - 2397. [Abstract] [Full Text] [PDF] |
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H. V. Huikuri, A. Castellanos, and R. J. Myerburg Sudden Death Due to Cardiac Arrhythmias N. Engl. J. Med., November 15, 2001; 345(20): 1473 - 1482. [Full Text] [PDF] |
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Task Force for the Diagnosis and Treatment of Chro, W. J. Remme, and K. Swedberg Guidelines for the diagnosis and treatment of chronic heart failure Eur. Heart J., September 1, 2001; 22(17): 1527 - 1560. [PDF] |
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F. Gaita, C. Giustetto, P. Di Donna, E. Richiardi, L. Libero, M. C. R. Brusin, G. Molinari, and G. Trevi Long-term follow-up of right ventricular monomorphic extrasystoles J. Am. Coll. Cardiol., August 1, 2001; 38(2): 364 - 370. [Abstract] [Full Text] [PDF] |
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D. Babuty and M. J Lab Mechanoelectric contributions to sudden cardiac death Cardiovasc Res, May 1, 2001; 50(2): 270 - 279. [Full Text] [PDF] |
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J. Mcmurray Beta-blockers, ventricular arrhythmias, and sudden death in heart failure: not as simple as it seems Eur. Heart J., August 1, 2000; 21(15): 1214 - 1215. [PDF] |
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