Contemporary Stress Echo Good For Risk Stratification In Chest-Pain Units

December 21, 2012

LONDON — Doctors in a London chest-pain unit have shown that employing contemporary stress echocardiography in patients with suspected acute coronary syndrome (ACS) but normal ECG and negative troponin is a successful approach for risk stratification [1].

Stress echo is feasible and safe and allows early triage and rapid discharge of patients, plus it is a good predictor of hard events, say Dr Benoy N Shah (Royal Brompton Hospital, London, UK) and colleagues in their paper published online December 18, 2012 in Circulation: Cardiovascular Imaging. Those with an abnormal stress echo had a 13- to15-fold increased risk of MI or death compared with those who had a normal stress echo, they report.

"Stress echo is a very effective gatekeeper for patients undergoing further risk stratification," senior author Dr Roxy Senior (Royal Brompton Hospital) told heartwire . "It helps select patients for coronary angiography [those with a positive stress echo] and allows immediate discharge of those patients with a negative result."

Stress echo is perceived to be a technique that is difficult, but that is a misconception.

But Senior says his chest-pain unit is the only one in the UK using this approach. "It is perceived to be a technique that is difficult, but that is a misconception. We have nine stress-echo operators, and it's easy to train people. With contemporary techniques, which employ contrast in around 50% of cases, the images are quite clear and quick and easy to interpret. It's very user-friendly. We want to show people around the world that it's a very doable technique, so why don't you use it?"

Stress echo also compares favorably with other tests used or proposed for risk stratification of such patients, he says. Exercise ECG is perhaps the most basic technique, "and we have shown that the downstream costs are lower with stress echo than with exercise ECG," given that the latter provides such equivocal results [2], he explained. And with regard to other imaging modalities that have been employed in this way, computed tomography coronary angiography (CTCA) and single-photon-emission computed tomography (SPECT) require the use of ionizing radiation and have other drawbacks, he notes.

Nevertheless, he and his colleagues say that further, multicenter studies comparing stress echo with CTCA, SPECT, and other imaging techniques for this purpose "will help determine the most cost-effective means of investigating this acute patient population."

Stress Echo Performed Within 24 Hours of Admission

Shah and colleagues say that after they showed in 2007 that stress echo was more cost-effective than exercise ECG, they have been employing the former in day-to-day practice in their unit to assess patients who come in with severe chest pain, but whose troponin is negative at 12 hours and whose ECG is "nondiagnostic" (ie, does not suggest any abnormality or shows only minor changes).

The current study is a retrospective look at the patients they have seen so far and is the first evaluation of the clinical impact of incorporating stress echo in a real-world chest-pain unit for the assessment of both short- and long-term prediction of hard events, they say.

"This was sort of an audit; we wanted to know, 'Is this right? Or are we overcalling it?' " Senior explains.

He says the stress echos are performed, for the most part, "within 24 hours" of admission to the chest-pain unit, from 9 am-5 pm Monday to Friday. Those admitted on a weekend will wait slightly longer for a stress echo, he acknowledged. The stress echo is performed on a treadmill if the patient is capable of exercise; if not, a pharmacological stress test is performed using dobutamine. Approximately 30% of the patients in this study performed the test on a treadmill, Senior noted.

Results of the stress echo are available quickly and, if negative, the patient is discharged immediately. If they are positive, the patient is investigated further.

Event Rate Much Higher for Those With a Positive Stress Echo

In the study, 839 consecutive patients were assessed; 802 were available for follow-up. Approximately 75% of them had a normal stress echo and were discharged.

"The 30-day readmission rate for all patients was extremely low," Senior notes, but for those with a negative stress echo it was exceedingly low (at 0.3% compared with 1.1% for those with an abnormal stress echo).

A normal stress echo carried a 99.7% event-free survival for death and 99.5% event-free survival for all hard events in the first year of follow-up; these event rates increased 15-fold and 13-fold respectively if the stress echo was abnormal.

There were 15 "hard" events, 0.5% in the normal stress echo group and 6.6% in the abnormal stress echo group in the first year. At two years, 2.3% of those in the normal stress echo group had died or had a nonfatal MI compared with 9.6% in the stress echo abnormal group, and at three years these figures were 5.1% and 21.1%, respectively. The median follow-up for the study was 27 months.

"For the patients who had a positive stress echo, the event rate was much higher," Senior notes. Of these 184 patients, 98 had ischemia and most of these underwent coronary angiography, with 57 demonstrating flow-limiting coronary artery disease and 30 subsequently undergoing revascularization.

Among all prognostic variables, only abnormal stress echo (hazard ratio 4.08) and advancing age (HR 1.78) predicted hard events in multivariable regression analysis.

Stress Echo Should Be Much More Widely Used in Chest-Pain Units

"This study demonstrates the excellent feasibility and safety of stress echo in a real-world chest-pain-unit setting, with rapid early triaging and discharge and accurate risk stratification," the researchers say.

"The two most important outcomes for patients reassured and discharged from the emergency department are that they do not suffer early mortality or early readmission with the same complaint. Our study highlights the excellent negative predictive value of stress echo and very low 30-day readmission rate."

In addition, the results show that stress echo "appropriately influences the use of coronary angiography and subsequent revascularization" and overall support the wider use of this technique in chest-pain units, they conclude.

Senior has previously received consultancy fees from Lantheus Medical. The coauthors report they have no conflicts of interest.