RSNA: Noninvasive CT angiography and stress tests can help predict which
patients are likely to suffer a heart attack or other adverse
cardiovascular event, according to a new study appearing online in the
journal Radiology. Cardiovascular disease is a leading cause of death worldwide. Bypass
surgery or stent placement is often recommended in people with certain
degrees of coronary arterial narrowing, or stenosis, but recent studies
have shown that many of these patients do just as well with medical
therapy. A key factor in treatment decisions is the hemodynamic
significance of the lesion, meaning the degree to which the lesion is
blocking blood from getting to areas of the heart.
“Previous studies show that a lesion is hemodynamically significant
if there is a significant blood pressure drop corresponding to a big
reduction in blood flow across the stenosis,” said study author João
A.C. Lima, M.D., from Johns Hopkins Hospital and School of Medicine in
Baltimore. “If plaque has those characteristics, the patient should be
targeted for intervention, be it with a stent or downstream bypass
surgery.”
A combination of invasive coronary angiography (ICA) and stress tests
with single photon emission tomography (SPECT) myocardial imaging has
been the gold standard for making these determinations, with ICA showing
the blockages and SPECT the perfusion, or penetration of the blood into
the tissue. However, ICA requires the use of a catheter that is
threaded from a puncture point in the groin all the way up to the heart.
“Invasive angiography is generally safe, but it can cause vascular
problems in a significant number of patients, most commonly at site of
the puncture,” Dr. Lima said. “In rare cases, it can cause strokes or
heart attacks. These risks are not trivial.”
The ICA/SPECT approach can also be expensive, as it often necessitates hospitalization for the patient.
“The traditional approach with invasive catheterization requires that
patients go to the hospital, get a catheter inserted into their leg and
go in for the nuclear SPECT study on a different day,” said study
coauthor Marcus Chen, M.D., from the National Institutes of Health in
Bethesda, Md. “Now with just one noninvasive test we can get two
important but different pieces of information about the coronary
arteries.”
The researchers set out to determine if combined CT angiography (CTA)
and CT myocardial stress perfusion imaging (CTP) could demonstrate
similar or superior ability to ICA/SPECT in predicting future adverse
events.
They compared the invasive and noninvasive approaches in 379 patients
who were referred for ICA from November 2009 to July 2011. The
researchers looked at the ability of both techniques to predict whether
or not a future major adverse cardiac event (MACE), such as a heart
attack, revascularization, arrhythmia or hospitalization for chest pain
or congestive heart failure would occur.
Fifty-one patients, or 13.5 percent, experienced one or more major
adverse cardiac events, including 49 revascularizations, five myocardial
infarctions, one cardiac death, nine hospitalizations for chest pain or
congestive heart failure, and one arrhythmia.
Both techniques proved to have similarly high values for predicting
MACE at two years after presentation and event-free survival. The
two-year MACE-free rates for combined CT angiography and CT perfusion
findings were 94 percent negative for coronary artery disease (CAD)
versus 82 percent positive for CAD and were similar to combined
ICA/SPECT findings (93 percent negative for CAD vs. 77 percent positive
for CAD).
“The key finding of our study is that both techniques are equally
effective in identifying which patients are going to have trouble down
the road,” Dr. Lima said. “The noninvasive option should be a preferred
or at least strongly considered option by cardiologists and radiologists
managing these patients because it is safer and less expensive, and
patients like it better.”
Obstacles remain before the noninvasive approach can achieve more
widespread use, including the lack of a reimbursement code for stress CT
perfusion. But the study indicates that the technique is relatively
easy to incorporate into existing practices: 15 of the 16 centers in the
trial had never done the procedure before, according to Dr. Chen, and
all were all able to learn it effectively.
