Patients Tested for Pulmonary Embolism with Subsequent Observation Unit Evaluation for Coronary Artery Disease: Implications for the

1
Patients Tested for Pulmonary Embolism with
Subsequent Observation Unit Evaluation for
Coronary Artery Disease Implications for the
Triple Rule Out CT Scan
Nafis Ahmed BS, Jennifer McCormick BS, Justin
Steinberg BS MBA, D. Mark Courtney, MD
Department of Emergency Medicine, Feinberg
School of Medicine, Northwestern University

• INTRODUCTION
• 6 million patients presented to US emergency
  departments in 2004 with chest pain. This chief
  complaint creates an enormous diagnostic
  challenge for physicians, who must effectively
  rule out life threatening etiologies like
  pulmonary embolism (PE), acute coronary syndrome,
  and aortic dissection in a timely manner. In most
  scenarios no single feature of the patients
  history, physical examination, or lab/ekg results
  provides a definitive diagnosis. Many of these
  patients are admitted to a 24 observation unit
  (OU), where serial enzyme testing and stress
  testing is done to further rule out coronary
  artery disease as the etiology of their
  symptoms.
• Many of these same patients are tested for PE in
  the ED, by a lengthy and resource intensive
  combination of D-dimer blood testing and CT
  scans. This is common because of 2 reasons
• Symptoms of PE (shortness of breath and chest
  pain) overlap symptoms of acute MI or angina.
• The same ultra-low threshold for missed cases
  motivates physicians to maximally use testing for
  both of these potentially life threatening
  conditions.
• This results in a situation whereby a low
  percentage of patients (3-5) overall who are
  evaluated either in the ED for PE or in the OU
  for symptomatic coronary artery disease in are
  found to be positive. A new and promising imaging
  modality, Multi-detector CT angiography (CTA) has
  been suggested as an alternative means of
  accurately imaging patients for both PE and
  significant CAD. This could eliminate the need
  for admission, serial enzyme measurements, and
  stress testing. It is also suggested that this
  imagining could evaluate for aortic dissection
  and provide the so called triple rule out
• However, If exceedingly low numbers of ED
  subjects are evaluated for both PE and CAD and/or
  if an exceedingly low amount of CAD is detected
  by the testing of these patients in OU pathways,
  then the adoption of a MDCT triple rule out
  algorithm would be less favorable from a utility
  and disease detection standpoint.

METHODS Study Design IRB approved prospective
study conducted at Northwestern Memorial
Hospitals Emergency Department over a span of
22 months. Sample ED Patients who underwent
diagnostic testing to evaluate for possible PE,
with subsequent admission to the OU for
detection of symptomatic coronary artery
disease. Exclusion Criteria Patients with
recent imaging for venous thromboembolism (VTEPE
or DVT), patients with concurrent therapeutic
treatment for VTE, or absolute inability to
perform follow-up. (homeless, incarcerated,
no-phone) Data Collection Data were
prospectively collected by study personnel at the
time of ED visit from the following sources ED
physicians, patient interview, and the medical
record. All information was entered into a web
based data collection instrument that prevented
any missing data, unified method of data entry,
and provided hyperlinks to define terms if
needed. Specific data collected at the index
visit included age gender chief complaint past
medical history of diabetes or hypertension
smoking history vitals signs test results and
ultimate discharge diagnosis. (from the ED our
the OU) Follow-up medical chart review, a
review of diagnostic tests performed, a telephone
interview in the event that NMH is not their
primary hospital, or a social security death
index search in the event that survival at 45
days cannot be proved by medical record review or
phone follow-up. Primary Outcome The proportion
of patients with abnormal troponin levels,
positive stress test, or ischemic changes on EKG
during evaluation in the Observation Unit or at
any time during the 45 day follow-up
period. Analysis Proportions and diagnostic
parameters were reported with 95 confidence
intervals.

.
DISCUSSION It is of interest that of all the
patients evaluated for PE, 71 are managed
without inpatient admission. Most of these are
negative for PE and discharged. The remainder are
fairly equally divided between inpatient care and
OU care. The rate of CAD disease detection in
this cohort was essentially zero. This may be
due to the low risk nature of these patients
which is defined by a preponderance of young,
female, non-smokers not likely to have
hypertension or diabetes. While MD CTA
evaluation for coronary artery disease could be
feasible in one quarter of all patients tested
for PE as an alternative to OU evaluation, it may
be unlikely to detect a significant amount of
disease.

• RESULTS
• A total of 1291 patients were tested for
  pulmonary embolism in the ED during this time.
• The overall rate of VTE was 5.3. All subjects
  diagnosed with PE in the ED at the time of index
  visit were admitted to the hospital.
• After negative ED evaluations for PE, 316/1291
  (26 95 CI 23-28) were admitted to the OU for
  further evaluation to rule out symptomatic CAD.
• Of these patients, 111/316 (35 30-41) had a
  CT in the ED prior to their CAD evaluation in the
  OU. The remainder had exclusive D-dimer testing
  in the ED, then went to the OU.
• The mean age of the EODU patients was 44.9
  years 43.7 to 46.0), and 64 were female.
• In the ED, 61 of sample patients presented
  with chest pain, 17 with dyspnea.
• Cardiac risk factors past or current smoking
  (34.5), hypertension (22), diabetes (4).
• Of all EDOU patients evaluated for PE, none had
  an abnormal troponin result or a positive stress
  test none had PE, DVT, or dissection at index
  visit or follow up.

• OBJECTIVE
• The following questions should be addressed as
  part of consideration of this approach
• What percentage of ED subjects evaluated for PE
  are also evaluated for CAD in an OU pathway?
• What percentage of these patients go on to have
  CAD detected in an OU?
• A secondary objective was the report general
  parameters of cardiac risk of patients who are
  tested initially in the ED for PE but who later
  go to the OU for evaluation of possible
  symptomatic CAD.

CONCLUSIONS The proportion of subjects who were
tested for PE in the ED who went on to get
further testing in the Emergency Department
Observation Unit was significant, but the rate of
detection of symptomatic CAD in these subjects
was very low. Targeted use in higher risk
samples or in situations likely to result in
false positive or negative stress tests may be
explored in future work. This work was supported
by the National Institutes of Health
(NHLBI) 5K23HL077404-03 (Courtney) Pretest
probability and D-dimer testing for PE