Friday June 6 2008
The new technique sucks out the clot before the surgery
“New heart attack operations cuts deaths” is today’s headline in The Daily Telegraph. The newspaper describes the study, which shows how deaths from heart attacks “could be halved” if the clots that cause heart attacks are removed before the surgery to re-open the artery begins.
The newspaper report is based on a Dutch study, which showed that only 3.6 per cent of patients who had the clot-removal procedure died in the year after their heart attack, compared with 6.7 per cent who received the usual treatment – percutaneous coronary intervention (PCI). This study will need to be repeated in other centres to indicate if there are any groups (for example those with large or small clots) who stand to benefit from the procedure.
Where did the story come from?
Dr Pieter J Vlaar and cardiology colleagues from the University Medical Center Groningen in the Netherlands carried out this research. The study was funded by the medical device manufacturer, Medtronic, and the Thorax Centre of the University Medical Center Groningen. It was published in the peer-reviewed medical journal: The Lancet.
What kind of scientific study was this?
The article reported on the one-year follow-up from a randomised controlled trial called the Thrombus Aspiration during Percutaneous coronary intervention in Acute myocardial infarction Study (TAPAS).
Percutaneous coronary intervention (PCI) is suitable for some patients with heart attacks: those that have a catheter (tube) inserted in the groin and fed into the coronary artery where a balloon is inflated to re-open the artery. A wire tube, called a stent, is usually placed to keep the artery open. This procedure needs to be performed within hours of the first symptoms to prevent death of the heart muscle. But often, researchers say, this leads to small fragments of the original clot travelling further down the artery. The new technique (thrombus aspiration) sucks the clot out of the artery before it is re-opened. This prevents the complications which may arise when the clot travels.
The researchers approached all patients who came to the centre with a type of heart attack known as ST-elevation myocardial infarction, which has specific characteristics on the initial ECG test. If they had no other diseases, had not received the clot-busting medical treatment (thrombolysis) and had a life expectancy of more than six months, they were randomly assigned either to the new thrombus aspiration treatment, or to conventional PCI treatment. Enrolment took place before the researchers knew the extent of the block in the heart; that is, before the patients had surgery. The researchers enrolled 1,071 patients over two years from 2005 to 2006. One year later, the researchers followed up 1,060 of the patients (99%) to find out whether they were still alive, had died from a heart-related cause, or had suffered a further heart attack.
What were the results of the study?
The researchers report that 19 of the 535 patients randomised to the new treatment (thrombus aspiration) group died from a heart-related cause by the end of the first year (3.6%). Also, 36 of the 536 patients in the control (conventional PCI) group had died (6.7%). This difference was statistically significant (hazard ratio 1.93; 95% CI 1.11–3.37; p=0.020).
When the researchers looked at the combination of one-year heart related death and non-fatal reinfarction, they found that either of these outcomes occurred in 5.6% of patients in the new treatment group, and 9.9% of patients in the control group. This was just under a halving of the risk, and was statistically significant.
What in terpretations did the researchers draw from these results?
The researchers conclude that “compared with conventional PCI, thrombus aspiration before stenting of the infarcted artery seems to improve the one-year clinical outcome after PCI for ST-elevation myocardial infarction.”
What does the NHS Knowledge Service make of this study?
This is a well-designed and reliable study, which has shown a clear difference in survival between the randomised groups. The graphs that illustrate the difference in survival also indicate that the difference can be attributed to improved survival within the first 30 days following the heart attack, as this is where the “survival curves” begin to separate from each other. This suggests that there are no longer-term problems with this new additional procedure. The researchers suggest two small limitations to their study:
- They designed the study and the target number of people to enrol (1,071) based on 66 expected deaths and 35 reinfarctions. This ensured that the study had the power to detect a difference, but it also meant they could not adequately investigate the effect of their technique on other clinical outcomes, such as heart failure or quality of life.
- No measurement of infarct size of the heart attack or the function of the heart muscle (left ventricular function) was done. This means that they were unable to suggest subgroups in which the procedure may be beneficial.
Overall, this is an important study because it has paved the way for future studies in other centres. Ideally, these studies should be large enough to allow analysis of subgroups of people with varying severities of heart attack.
Sir Muir Gray adds...
A well designed, well conducted study, but a single study is rarely enough on its own; what we need are more studies and then a systematic review of all the trials.