Discussion
Our study found that CV testing among patients with CV risk factors and
without known heart disease occurs in about a third of patients at the
highest level of SCD risk. Those in the highest SCD risk categories had
a trend for more testing but this peaked at approximately one third of
the patients. This higher rate of testing in those at highest SCD risk
was associated with a 7% all cause mortality rate and a 45% chance of
developing sudden death over 10 years. The strengths of these findings
are supported by the use of data from two large academic centers, the
diversity of the sample, the large cohort and the consistency of the
findings.
Screening populations for SCD is a significant
challenge.1, 15 Out of hospital cardiac arrest is a
leading cause of death among adults in the United States (approximately
300,000 events per year).1 Even though the risk of SCD
is higher in patients with heart failure and/or advanced
cardiomyopathies, the majority of SCD cases occur in the general
population with cardiovascular risk factors and no known heart
disease.23 Identifying people at risk of SCD without
known heart disease is therefore challenging.15 Left
ventricular ejection fraction (LVEF) is a strong predictor of SCD, but
it is neither sensitive nor specific.17 Furthermore,
population screening for ventricular function is not practical nor
recommended for routine clinical practice.4, 16 This
inverse relationship between risk (or incidence) and actual cases of SCD
was initially highlighted by Myerburg et al.2 To date,
there has been no systematic attempt to address SCD in the general
population.
The first major breakthrough to enable risk stratification for SCD in
the general population was the development of a simple clinically based
risk score that could provide risk stratification for SCD in the general
population. Bogle et al developed a risk model from ARIC and validated
it in the Framingham study. Model covariates included age, sex, total
cholesterol, lipid-lowering and hypertension medication use, blood
pressure, smoking status, diabetes, and body mass index. The profile of
risk score by decile yielded an exponential curve with the bulk of the
SCD risk in the upper two deciles. While other risk scores have been
proposed, they all include variables that may not be uniformly available
in a primary care setting, such as an ECG. In our primary care cohorts,
90% of patients had all the variables required to calculate this risk
score. One can argue that all of the variables in this risk score should
be documented in the medical record.
In the report by Bogle et al, the predicted and observed 10-year rates
of SCD in the upper two deciles were in the 2-6% range. While this is a
substantial risk, it is not actionable as it is still fairly low and
there are no identified targets for treatment. With this background, the
current study was designed to identify how frequently these high risk
patients are undergoing cardiac evaluation. These patients have a very
high burden of cardiovascular risk factors. It is therefore possible
that these patients have significant subclinical cardiovascular disease
that can only be identified by cardiac testing. We demonstrate a very
low rate of cardiac testing in this high risk population, and therefore
identify a potentially practical opportunity to identify subclinical
cardiac disease that could be targeted for treatment that may ultimately
prevent SCD.
While this approach requires careful evaluation to establish its
efficacy, this is a paradigm shifting approach. Currently, the three
main bodies writing preventive cardiac guidelines do not support
screening of asymptomatic individuals. Second, it is not cost-effective
to screen for CV diseases in all patients seen. Third, insurance will
not reimburse for asymptomatic testing and physicians do not order them
because patients are not willing to pay out of pocket. However,
echocardiograms in asymptomatic primary care patients have been able to
identify incident cases of systolic and diastolic dysfunction which in
turn lead to changes in treatment and this screening strategy has been
proven to be cost-effective.5, 6 As it would be
cost-prohibitive to perform testing on all patients seeking care in the
United States, testing in the highest risk deciles may be more
practical. There is a clear need to act on the diagnostic gap identified
in this study.
The nature of the further cardiac testing to recommend in these high
risk deciles is certainly not established. Our group has found that
testing seniors in a primary care practice using echocardiography can
identify new HF patients and those with heart failure with preserved
ejection fraction.5, 6 We also have documented that by
informing the clinicians of the echocardiogram findings there is
medication intensification, improvement in CV risk factors and lower
operative costs.18 Also adding echocardiographic
information to the SCD score improves the ability of the combined score
to predict mortality.19
There are several limitations that deserve mention. First, we relied on
ICD codes to identify comorbidities and used this as an exclusion
criteria, this could have excluded patients with HF or CAD when the
condition was not present. However, we conducted a chart review in a
small sample and found that the accuracy of the codes was 100%. Second,
we used a cross-sectional design to evaluate the outcome and this could
have undercounted the number of procedures performed. However, we used
period prevalence to calculate the procedures over time. Third, patients
could have had their procedures done at other institutions and this
could have led to undercounting of the procedures. Fourth, the
generalizability of our findings is limited to the two medical centers
included in the study.
In conclusion, this study provides evidence that the majority of
patients from the general population at elevated risk for SCD based on a
novel SCD risk score do not undergo any CV testing. We propose a new
paradigm of further cardiac screening for these asymptomatic patients to
identify subclinical cardiac disease that leads to SCD. Future studies
should evaluate what the appropriate testing is and the therapeutic
strategies to implement for those at risk.
Table 1: Baseline characteristics by SCD risk: A) University of Miami B)
Vanderbilt University
A)