Discussion
Our study provides a contemporary assessment of maternal
and neonatal risk associated with pregnancy in women with
heart disease who are receiving comprehensive prenatal care.
The cardiac event rate in the present study (13%) is lower
than that reported in a recent retrospective study (18%).9 In
the present study, patients referred for consultation only
(likely a lower risk group) were eligible for enrollment; they
were excluded in the retrospective study. Therefore, the
present study population may be more representative of the
total population at risk. The fetal/neonatal mortality rate (2%)
and rate of preterm labor (10%) was higher than that reported
in a Canadian study examining outcomes in a general
obstetric population (0.3% and 4%, respectively),17 whereas
the frequency of PIH in the present study (4%) was identical.
Poor NYHA class, cyanosis, myocardial dysfunction, prior
arrhythmia, and prior heart failure/stroke have been previously
identified as risk factors for maternal cardiac events.1–3,9 The
present study extends the results of previous studies by quantifying
these risks prospectively in a large patient group recruited
across Canada. The revised risk index is simpler than the
original9 but has identical accuracy. Furthermore, it can be
applied to a composite outcome that includes decline in functional
class or need for urgent invasive cardiac intervention, in
addition to the primary cardiac end points.
Poor NYHA class or cyanosis was predictive of neonatal
events in prior studies and in the present study.2,9 The
predictive role of maternal left heart obstruction on neonatal
outcome identified in this study may be mediated by inadequate
placental perfusion, which then results in fetal growth
retardation or premature labor. Concerns about maternal
deterioration may have also led to preterm induction. Coarctation
of the aorta was a predictor for PIH, reflecting
abnormal response in the aorta in these patients.18 Nulliparity
and systemic lupus erythematosus have also been reported to
be risk factors for PIH in the general obstetric population.19
The association between cyanosis and PPH is likely related to
the known hemostatic defects in patients with cyanotic heart
disease.20
Pulmonary hypertension in the absence of Eisenmenger
syndrome was not an independent predictor, probably because
of its association with other predictors such as poor
functional status or left heart obstruction. Whether reactive
pulmonary hypertension resulting from mitral stenosis confers
a lower mortality risk than that resulting from fixed
pulmonary vascular disease remains to be determined.
In conditions with known lesion-specific risks, such as
Marfan syndrome, this index will supplement lesion-specific
predictors.21 The risk associated with cardiac lesions, which
were not well represented in this study (such as Fontan
procedure or hypertrophic cardiomyopathy), may have been
underestimated. Until additional data are available, clinical
management of patients with such conditions should be based
on an assumption of intermediate risk.
The strategy of combining cardiac lesions and deriving a
common risk index is similar to that used in the risk
stratification of patients undergoing noncardiac surgery.22 In
our study, the cohort was defined by its exposure to the
cardiovascular changes of pregnancy. This strategy also
allowed for the analysis of multiple cardiac lesions within the
same woman. Predictors (NYHA class and ventricular function)
identified in our study have also been cited as prognostic
factors in lesion-specific studies.6–8
The selection bias associated with patient recruitment from
regional centers was minimized by the fact that these centers
received referrals from wide catchment areas. Because the
Canadian health care system provides universal access, we
expect that only patients at negligible risk would not be
Frequency of maternal primary cardiac events, as predicted by
the risk index and observed in the derivation and validation
groups, expressed as a function of the number of cardiac predictors
or points.
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referred to a regional center. Although treatment strategies
were not standardized in this study, regional variation was
minimized by the fact that the participating centers (part of
the Canadian Adult Congenital Heart Network) used common
practice guidelines.23
In women at high risk for cardiac events, cardiac interventions
should be considered before conception if the riskbenefit
ratio is favorable. Women at intermediate or high
cardiac risk (risk score $1 or with lesion-specific risk factors)
should be referred to a regional center for ongoing care.
Those at low cardiac risk (risk score of 0 and without
lesion-specific risk factors) can safely deliver in a community
hospital. Women with risk factors