Article

Use of implantable cardioverter defibrillators for primary prevention in the community: Do women and men equally meet trial enrollment criteria?

University of Colorado Denver, Division of Cardiology, 12631 E. 17th Ave., Mailstop B130, PO Box 6511, Aurora, CO 80045, USA.
American heart journal (Impact Factor: 4.46). 09/2009; 158(2):224-9. DOI: 10.1016/j.ahj.2009.05.018
Source: PubMed
ABSTRACT
Fewer women than men undergo implantable cardioverter defibrillator (ICD) implantation for the primary prevention of sudden cardiac death. The criteria used to select patients for ICD implantation may be more permissive among men than for women. We hypothesized that women who undergo primary prevention ICD implantation more often meet strict trial enrollment criteria for this therapy.
We studied 59,812 patients in the National Cardiovascular Data Registry ICD registry undergoing initial primary prevention ICD placement between January 2005 and April 2007. Patients were classified as meeting or not meeting enrollment criteria of either the MADIT-II or SCD-HeFT trials. Multivariable analyses assessed the association between gender and concordance with trial criteria adjusting for demographic, clinical, and system characteristics.
Among the cohort, 27% (n = 16,072) were women. Overall, 85.2% of women and 84.5% of men met enrollment criteria of either trial (P = .05). In multivariable analyses, women were equally likely to meet trial criteria (OR 1.04, 95% CI 0.99-1.10) than men. Significantly more women than men met the trial enrollment criteria among patients older than age 65 (86.6% of women vs 85.3% of men, OR 1.11, 95% CI 1.03-1.19), but this difference was not found among younger patients (82.5% of women vs 83.0% of men, OR 0.97, 95% CI 0.89-1.07).
In a national cohort undergoing primary prevention ICD implantation, older women were only slightly more likely then men to meet the enrollment criteria for MADIT II or SCD-HeFT. Relative overutilization in men is not an important explanation for gender differences in ICD implantation.

Full-text

Available from: Yongfei Wang, Jan 18, 2014
Electrophysiology
Use of implantable cardioverter defibrillators for
primary prevention in the community: Do women
and men equally meet trial enrollment criteria?
Stacie L. Daugherty, MD, MSPH,
a,b
Pamela N. Peterson, MD, MSPH,
a,b,c
Yongfei Wang, MS,
d
Jeptha P. Curtis, MD,
b,d
Paul A. Heidenreich, MD,
e,h
JoAnn Lindenfeld, MD,
a
Humberto J. Vidaillet, MD,
f,g
and
Frederick A. Masoudi, MD, MSPH
a,b,c
, on behalf of the NCDR Aurora and Denver, CO; New Haven, CT;
Palo Alto, CA; and Marshfield, WI
Background Fewer women than men undergo implantable cardioverter defibrillator (ICD) implantation for the primary
prevention of sudden cardiac death. The criteria used to select patients for ICD implantation may be more permissive among
men than for women. We hypothesized that women who undergo primary prevention ICD implantation more often meet strict
trial enrollment criteria for this therapy.
Methods We studied 59,812 patients in the National Cardiovascular Data Registry ICD registry undergoing initial
primary prevention ICD placement between January 2005 and April 2007. Patients were classified as meeting or not meeting
enrollment criteria of either the MADIT-II or SCD-HeFT trials. Multivariable analyses assessed the association between gender
and concordance with trial criteria adjusting for demographic, clinical, and system characteristics.
Results Among the cohort, 27% (n = 16,072) were women. Overall, 85.2% of women and 84.5% of men met enrollment
criteria of either trial (P = .05). In multivariable analyses, women were equally likely to meet trial criteria (OR 1.04, 95% CI 0.99-
1.10) than men. Significantly more women than men met the trial enrollment criteria among patients older than age 65 (86.6% of
women vs 85.3% of men, OR 1.11, 95% CI 1.03-1.19), but this difference was not found among younger patients (82.5% of
women vs 83.0% of men, OR 0.97, 95% CI 0.89-1.07).
Conclusions In a national cohort undergoing primary prevention ICD implantation, older women were only slightly more
likely then men to meet the enrollment criteria for MADIT II or SCD-HeFT. Relative overutilization in men is not an important
explanation for gender differences in ICD implantation. (Am Heart J 2009;158:224-9.)
Recent clinical trials have expanded indications for
implanta ble c ardioverter defibrillators (ICDs) for the
primary prevention of sudden cardiac death.
1,2
However,
many eligible patients do not receive this therapy,
3-5
and
previous studies have demonstrated that certain groups,
specifically women, are less likely to be referred for
primary prevention ICD therapy.
3-7
Existing evidence and guidelines do not support the
differential use of ICD therapy according to gender.
Although women constitute only approximately 20% of
the patient population in the large primary prevention
trials for ICD therapy, there is no evidence that the benefits
of ICD therapy vary by gender.
1,2,8,9
Current practice
guidelines ba sed on these trials recommend primary
prevention ICD therapy in both women and men with
severe left ventricular systolic dysfunction.
10,11
Possible
explanations for observed gender differences in ICD
implantation rates include that fewer women may be
truly eligible for ICD therapy, that a disproportionately
smaller number of eligible women are referred for ICD
therapy, or that the criteria used to select women for ICD
implantation in practice are more stringent.
We sought to compare the extent to which women
and men receiving ICD therapy in the United States
conform to the criteria for patient selection based on
major clinical trials. We hypothesized that, given prior
evidence that women are less likely to be referred for
primary prevention ICD therapy, women who actually
From the
a
University of Colorado Denver, Aurora, CO,
b
Institute for Health Research,
Kaiser Permanente of Colorado, Denver, CO,
c
Denver Health Medical Center, Denver,
CO,
d
Yale University, New Haven, CT,
e
VA Palo Alto Health Care System, Palo Alto, CA,
f
Marshfield Clinic Research Foundation, Marshfield, WI, and
g
Marshfield Clinic,
Marshfield, WI.
h
The author is a consultant to Boston Scientific, Natick, MA.
Submitted December 10, 2008; accepted May 12, 2009.
Reprint requests: Stacie Luther Daugherty, MD, MSPH, Division of Cardiology, 12631 E.
17th Ave., Mailstop B130, PO Box 6511, Aurora, CO 80045.
E-mail: stacie.daugherty@ucdenver.edu
0002-8703/$ - see front matter
© 2009, Mosby, Inc. All rights reserved.
doi:10.1016/j.ahj.2009.05.018
Page 1
undergo ICD implantation would be more likely to meet
these criteria.
Methods
Data source
We used data from the National Cardiovascular Data Registry's
(NCDR) ICD Registry, which was developed in 2005 in response to
a mandate by the Center for Medicaid and Medicare Services to
characterize patients receiving primary prevention ICD therapy.
12
Implanting centers must enter data into the registry on Medicare
beneficiaries receiving primary prevention ICDs to obtain
reimbursement for these procedures. Enrollment of non-Medicare
patients is voluntary, although approximately 80% of participating
hospitals register all ICD recipients, regardless of indication or
insurance status.
13
Implanting centers submit data quarterly using
American College of Cardiology certified software and data quality
is examined using the data quality reporting process.
13,14
Implanting centers must enter complete and accurate data to
receive Medicare reimbursement. The registry contains detailed
and standardized data elements related to baseline patient clinical
characteristics, device used, and in-hospital outcomes.
Study population
All patients within the NCDR-ICD registry who underwent ICD
implantation between January 200 5 and April 2007 were
considered for inclusion. Patients with missing gender informa-
tion and those receiving ICD therapy for secondary prevention
were excluded from the analyses. Patients were also excluded if
they had received a prior ICD. Thus, all patients in the study
cohort underwent first-time ICD implantation for the primary
prevention of sudden cardiac death.
Independent variables
For all analyses, the primary independent variable was patient
gender. Additional variables considered in the multivariable
models included hospital admission characteristics (age, race,
insurance payer, reason for hospitalization); patient comorbid-
ities and risk factors (history of congestive heart failure, atrial
fibrillation or flutter, ca rdiac t ransplantation, etiology of
cardiomyopathy, myocardial infarction, coronary artery bypass
grafting, percutaneous coronary intervention, valvular surgery,
cerebrovascular disease, pacemaker insertion, chronic lung
disease, diabetes, hypertension, estimated glomerular filtration
rate [from the Modification of Diet in Renal Disease Study
equation]
15
and admission New York Heart Association [NYHA]
classification); diagnostic and procedural information (ejection
fraction, whether an electrophysiology study was performed,
electrophysiology study results, QRS duration, PR interval,
presence of atrial or ventricular conduction delays, blood urea
nitrogen, sodium level, brain natriuretic peptide level, systolic
blood pressure, ICD type [single-chamber, dual-chamber, or bi-
ventricular device], and lead implantation method); and
physician and hospital characteristics (whether implanting
physician is certified in electrophysiology per self report, for-
profit or not-for-profit hospital, rural or nonrural hospital,
hospital teaching status, number of beds, and number of ICD
implantations at each hospital).
The rate of missing data was extremely low for all variables
(b0.5%, with the exception of left ventricular ejection fraction,
which was missing in 1.5%). To avoid case-wise deletion of
those cases with missing data points, the missing values were
imputed. The missing categorical variables were imputed as the
most common value among those with the data present. For
example, in the categorical variable NYHA class (missing =
0.15%), missing variables were imputed as class I. For
continuous variables, the missing values were imputed as the
median among those with the data present. Dummy variables
were constructed to indicate when the variable was missing. In
the multivariable models, both the imputed values and the
dummy variable were included.
Dependent variables
For all analyses, the primary dependent variable of interest was
whether enrollment criteria for either the MADIT II or SCD-HeFT
trial were met. Patients were considered to have met MADIT II
criteria if they had (1) a prior myocardial infarction (MI); (2) the
MI occurred N40 days before implantation; (3) a left ventricular
ejection fraction (LVEF) 30%; and (4) NYHA class I, II, or III
symptoms.
2
Patients were considered to have met SCD-HeFT
criteria if they had (1) a history of heart failure regardless of
etiology, (2) an LVEF 35%; and (3) NYHA class II or III
symptoms.
1
Patients meeting either of these definitions were
designated as meeting trial enrollment criteria. Patients with
NYHA class IV symptoms were also considered to qualify if (1)
they met either MADIT II or SCD-HeFT indications other than
symptom severity, (2) had an intraventricular conduction delay,
and (3) received a biventricular ICD.
10
Statistical analysis
Baseline clinical characteristics between women and men
were compared using the χ
2
test for categorical variables and t
tests for continuous variables. To assess the i ndependent
relationship between gender and concordance with trial
enrollment criteria for ICD therapy, hierarchical logistic regres-
sion was used, adjusting for patient, provider, hospital,
Figure 1
Study population of women and men from 1107 sites in the United
States.
Daugherty et al 225
American Heart Journal
Volume 158, Number 2
Page 2
procedural characteristics, and accounting for the clustering of
patients within hospitals. Because of the large sample size,
nonparsimonious models could be used.
Given current Center for Medicaid and Medicare Services
reimbursement rules, it is possible that gender differences may
vary based on Medicare coverage. Therefore, in secondary
analyses, patients were stratified by age (b65 and 65 years
old). Multivariable hierarchical logistic regression models were
constructed considering the same covariates as the primary
analysis models. The stati stical significance of differences
among strata was tested with 2-way interaction terms in the
full model. All analyses were performed using the SAS statistical
package version 9.1 (SAS Institute, Cary, NC). A P value of b.05
was deemed significant, and all reported P values are 2-sided
except where appropriate.
This research was supported by the NCDR. Dr Peterson is
supported by an American Heart Association Pharmaceutical
Roundtable Award. The authors were solely responsible for the
design and conduct of this study, all study analyses, and the
drafting and editing of the paper.
Results
Study population
A total of 107,723 patients (26% women vs 74% men)
who underwent ICD implantation from January 2005
Table I. Baseline characteristics
Description
Gender
PMale (n = 43740) Female (n = 16072)
Admission characteristics
Age (mean ± SD) 68.2 ± 12.2 67.6 ± 12.8 b.001
Race b.001
White 83.2 76.5
Black 11.3 18.2
Other 5.5 5.3
Hispanic ethnicity 5.4 5.4 .95
Insurance payer b.001
Medicare 70.7 70.8
Medicaid 3.8 5.8
Commercial 16.2 15.0
Health maintenance organization 6.1 5.6
Other 3.2 2.8
History and risk factors
Congestive heart failure 83.2 88.3 b.001
New York Heart Association current status b.001
Class I 10.1 7.3
Class II 35.3 29.8
Class III 50.0 57.2
Class IV 4.7 5.7
Nonischemic dilated cardiomyopathy 28.1 47.0 b.001
Ischemic cardiomyopathy 71.6 51.1 b.001
Atrial fibrillation/flutter 32.3 25.7 b.001
Previous myocardial infarction b.001
Within 40 d of ICD implant 5.7 4.5
More than 40 d before ICD implant 50.1 34.3
Previous coronary artery bypass grafting 41.5 23.1 b.001
Previous percutaneous coronary intervention 34.0 25.9 b.001
Cerebrovascular disease 14.3 13.4 .005
Chronic lung disease 21.3 22.4 .003
Diabetes 37.3 39.1 b.001
Hypertension 73.3 72.0 .001
Glomerular filtration rate b60 mL/min 40.3 54.7 b.001
Diagnostics
% Ejection fraction (mean ± SD) 24.9 ± 7.8 24.8 ± 8.5 .26
Electrophysiology study done 10.1 8.6 b.001
QRS duration (ms) (mean ± SD) 128.5 ± 34.6 128.2 ± 34.6 .36
Abnormal intraventricular conduction 56.7 58.7 b.001
BNP level (pg/mL), when drawn (mean ± SD) 1033.6 ± 1119.2 1099.5 ± 1164.1 .004
ICD type b.001
Single chamber 25.8 23.9
Dual chamber 35.1 30.2
Biventricular 38.8 45.7
All expressed as percent unless otherwise specified.
BNP, Brain natriuretic peptide.
226 Daugherty et al
American Heart Journal
August 2009
Page 3
through April 2007 were considered for inclusion into the
study cohort. Among these, 115 were missing gender
information. Another 39,832 were excluded for secondary
prevention ICD indications (22,281 with secondary
prevention indicated on case reporting form; another
12,485 with history of syncope, 1,602 with history of
tachycardic cardiac arrest, and 3,464 with history of
sustained ventricular tachycardia). A total of 7,964
patients had received a prior ICD resulting in a final
study cohort of 59,812 patients undergoing first-time ICD
implantation for primary prevention, of which 27% were
women and 73% were men (Figure 1).
Demographic and clinical characteristics
Women were slightly younger (mean age ± SD: women
67.6 ± 12.8, men 68.2 ± 12.2, P b .001) and more often
black (18.2% vs 11.3%, P b .001) compared with men.
Substantially more women had a nonischemic cardiomyo-
pathy (47.0% vs 28.1%, P b .001) and slightly more had a
history of heart failure (88.3% vs 83.2%, P b .001). Women
had more advanced heart failure symptoms (NYHA class
III or IV 62.9% vs 54.7%, P b .001) than men. The mean
ejection fraction (%) was not significantly different
between women and men (mean ± SD 24.8 ± 8.5 vs
24.9 ± 7.8, P = .26) (Table I).
Concordance with trial criteria
Among the final study cohort receiving primary
prevention ICD therapy, 84.7% met either the MADIT-II
or SCD-HeFT trial enrollment criteria. The overall propor-
tion of patients meeting trial criteria was slightly higher for
women than for men (85.2% vs 84.5%, P = .05). In the
group of patients who did not meet inclusion criteria for
either trial, women tended to have a higher NYHA
symptom class, lower ejection fractions, were more likely
to have a history of heart failure, and were less likely to
have a prior MI compared to men (Table II).
In multivariable analyses, women and men were equally
likely to meet overall trial criteria after accounting for
admission characteristics; medical history; NYHA class;
diagnostic, physician, and hospital characteristics; and
clustering of patients among hospitals (OR, 1.04; 95% CI
0.99-1.10).
Secondary analyses
A significant interaction was found between gender and
age group (P = .002). When stratified into groups of 65
years old, younger women and men were equally likely to
meet trial enrollment criteria (crude proportions of 82.5%
vs 83.0%, P = .37; fully adjusted OR 0.97, 95% CI 0.89-
1.07). However, among those 65 years old, women were
significantly more likely than men to meet these criteria
(crude proportions of 86.6% vs 85.3%, P b .01; adjusted
OR 1.11, 95% CI 1.03-1.19) (Figure 2).
Discussion
This study of patterns of care in 1107 institutions in the
United States found that most patients receiving primary
prevention ICD therapy in practice meet enrollment
criteria for the major clinical trials. Furthermore, after
adjustment for patient and health system factors, men
were as likely to meet these criteria as women. This
finding varied according to age group with older women
having 11% greater odds than men of meeting trial criteria.
However, the absolute difference in this proportion
(1.3%) was modest, suggesting that relative overutilization
in men is not a major contributor to gender differences in
the use of ICD therapy.
Table II. Characteristics of women and men receiving ICDs
who did not meet either the MADIT II or SCD-HeFT trial
enrollment criteria
Baseline charcteristics
Men
N = 6769
Women
N = 2382 P value
NYHA Class b.001
I 36.3 35.0
II 31.7 28.0
III 18.1 20.7
IV 13.9 16.2
Left Ventricular Ejection Fraction b.001
N35% 21.1 23.3
30-35% 31.7 22.8
b30% 47.3 53.9
Prior Heart Failure b.001
No 60.8 54.5
Yes 39.2 45.5
Prior MI b.001
No 58.4 72.9
Yes; 40 days of implant 11.2 7.6
Yes; N40 days of implant 30.4 19.4
Figure 2
Adjusted odds of meeting trial enrollment criteria in women and men
stratified by age group.
Daugherty et al 227
American Heart Journal
Volume 158, Number 2
Page 4
Our study suggests women represent 27% of patients
receiving ICDs for primary prevention in contemporary
clinical practice in the United States. This proportion is
similar to that identified in single-center studies that have
found that women represent a minority of those receiving
ICD therapy for either primary or secondary prevention,
with the greatest gender differences among those receiv-
ing primary prevention therapy.
4,6,7,16
More recently,
reports using data from the Medicare population also
demonstrate consistently lower rates of ICD use in women
over time.
4,5
The lower rates of ICD therapy in women
raises important questions as to why these gender
differences occur.
One possible explanation for lower ICD implantation
rates in women is that the criteria used to select patients
for implantation are applied more stringently to women.
Possible reasons for such a difference might include
provider belief that women are less likely to benefit from
ICD therapy, provider concern for higher complications
rates of ICD implantation in women, or provider gender
bias.
16
For example, if there were widespread belief that
ICD therapy is less efficacious in women then in men,
then we would expect that women who actually receive
ICD therapy would be more likely to meet stringent trial
criteria or that trial criteria would be applied more
permissively in men. In this study, we found that women
and men were equally likely to meet trial criteria after
consideration of a wide range of other patient character-
istics. Therefore, a relative overuse of ICDs in men does
not appear to explain the large variation seen in the
overall use of ICD therapy among women and men.
A second possible explanation for the lower use of ICD
therapy in women is a disproportionate underreferral of
eligible women compared to men. Prior work has shown
women are less commonly referred for invasive cardiac
procedures compared to men.
17-20
A recent study by
Hernandez et al investigated whether women are less
often referred for ICD therapy. Using American Heart
Association Get With The Guidelines data for patients
hospitalized for heart failure, they found that among
eligible patients, only 35% received ICD therapy and
eligible women were 40% less likely to receive an ICD
than eligible men.
3
Although this study provides
significant evidence for disparate ICD referral patterns
among women and men hospitalized for heart failure,
questions still remain regarding gender differences in
eligible outpatients. The findings of this study suggest
that most of the variation in ICD use by gender may be
related to upstream factors such as an underreferral of
women wh o meet ICD eligibility criteria or fewer
women than men in the general population actually
meet ICD eligibility criteria.
Another important finding of our study is the influence
of age on the gender differences identified. Our findings
suggest trial criteria are being applied more stringently
among older women than older men with no significant
gender differences among younger patients. Given that
the NCDR provides clear guidelines for the reimburse-
ment of ICD therapy among Medicare beneficiaries, our
finding that gender differences are confined to the older
cohort and not found in the younger cohort where
reimbursement guidelines are less stringent is unex-
pected. Similar to other invasive procedures, this finding
may reflect providers' reluctance to recommend ICD
therapy among older women who may have more
coexisting illnesses and higher complication rates and
are therefore viewed as less likely to benefit from
therapy.
16,21
However, even after controlling for many
important clinical characteristics, including coexisting
illnesses, this difference persisted. Another possible
explanation for this age-specific finding is that older
women may be more likely to refuse ICD therapy
compared to men. Some studies have suggested older
women are slightly more likely to refuse certain invasive
cardiac procedures; yet, the absolute differences in
refusal rates in these studies were small and unlikely to
explain all of the gender variation observed in the use of
invasive technologies.
22,23
Additional studies are needed
to distinguish the extent to which d ifferences in
provider and pa tient att itude s toward ICD therapy
account for variation in ICD implantation between
women and men.
Finally, this study highlights the va lue of large,
contemporary national registries to study the application
of new technologies applied in real world settings.
National registries are ideal for monitoring technology
utilization, safety, and effectiveness on a national scale in
representative populations. Furthermore, results from this
and other studies using the NCDR registries overcome the
potential lack of applicability of single-center studies or
those confined only to Medicare beneficiaries, and extend
the findings of existing studies by focusing on ICD use in
contemporary practice.
When considering these results, a few limitations should
be noted. First, although we were able to study a large
national cohort of pati ents w ho underwent primary
prevention ICD therapy, we were not able to study
eligible patients who were not referred for therapy or
who were referred but did not undergo ICD implantation.
Thus, we were unable to examine whether referral bias or
patient preferences explain the differences observed.
Furthermore, among patients who did not meet trial
criteria, it is possible that extenuating circumstances not
reflected in the data collection motivated the decision to
pursue ICD implantation. Finally, data in the NCDR
registry are self-reported by hospitals and failure to meet
trial enrollment criteria may be underreported. However,
there is no substantial incentive to underreport cases that
do not meet trial criteria as reimbursement is not
dependent on achieving trial concordance. Furthermore,
it is unlikely that patterns of reporting trial concordance
would vary by patient gender.
228 Daugherty et al
American Heart Journal
August 2009
Page 5
Conclusion
We found that among patients undergoing ICD implan-
tation for primary prevention, older women were only
slightly more likely to conform to the enrollment criteria
of clinical trials than older men, suggesting that gender
differences in ICD therapy is not related to a dispropor-
tionate overutilization among men who do not meet trial
criteria. Additional studies are needed to further define the
extent to which other factors, such as a smaller population
of eligible women, the underreferral of eligible women, or
gender differences in patient preferences contribute to
gender differences in the use of ICD therapy.
Disclosures
This research was supported by the National Cardiovas-
cular Data Registry. Dr Peterson is supported by an
American Heart Association Pharmaceutical Roundtable
Award (ID no. 0670017N).
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Volume 158, Number 2
Page 6
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