Friday, November 06, 2009


When I was in training, coronary artery bypass surgery ( CABG ) was at its infancy and we were so excited that we could stop beating heart and attached good venous conduits on to the affected coronary artery, creating a new channel and restoring full or even supra-full blood flow. The we began to see that the venous conduits ( the veins from the legs ) were convenient conduits, but tended to re-occluded. You see when God made the veins for us, He made it to withstand pressures of 5-10 mmHg pressure. When Dr Rene Favaloro taught us to attach the veins to the arterial system, it had to take the pounding of the arterial blood pressure, which is most situation was 120-140 mmHg systolic. So the venous conduits hardened, and re-occluded. re-operations became hazardous. Then Dr Green and colleague began to start using the left internal mammary artery as the prefered conduit for bypassing the vital LAD ( left anterior descending artery ). This was great. The LIMA graft lasted well ( artery-artery ) and allowed CABG to have good outcomes. Only venous graft by-pass must have died with the late Dr Victor Chiang ( God rest his soul ), a great cardiac surgeon with very good venous graft results. He always say that the venous graft patency is not only a function of the blood pressure that it is subjected too, but also to the technique and skill ( atraumatic technique ) in harvesting the venous graft. His fellows are all well trained for that.
Then some physicians noted that some patients post-CABG seemed to develope some cognitive disorders. They began to say the wrong things, have a change in mood ( mood swings ) and also became forgetful. They wondered whether this was due to the use of the heart-lung machine used to maintain the circulation, while the cardiac surgeon was working on the non-beating heart. ( Tubes divert the normal circulation to the heart-lung machine to oxygenate the blood, remove the carbon dioxide, through filters, and then return in purified blood, back into the circulation. Basically it the machine takes the place of the heart and lungs ). The prevailing thought then was that the heart-lung machine maybe allowing particles to circulate to the brain causing the cerebral cognitive disprders, seen post-bypass. It could also be that when the cardiac surgeon cross clamps the aorta, to stop the circulation and divert it to the heart-lung machine, debris could be thrown off by the action of the cross clamp.
This gave rise to some American cardiac surgeon experimenting with a technigue of trying to do bypass surgery on a beating heart. They began to develop equipment and technique to minimise the force of contraction of the beating heart to allow them to sow on the venous or arterial conduit. They were able to develop clamps that will stick on to portions of the heart to stop the heart beating, focally, so that they can sow. One must also understand that this was also at an era of " minimally invasive surgery" to try and improve the pain in surgical procedures and also the cost. Patients were told ( without much clnical data to start ) that off-pump ( or beating heart ) surgery was just as good as standard on-pump bypass surgery ) with a smaller scar, less mental disorders post bypass, and less days of stay in hospital. This looks like wishful thinking, on almost no clinical data.
Well, then more and more studies comparing on-pump and off-pump surgery began to emerge with some countries ( like Canada ) keeping long-term registries. It became clear, that many of the claims were flawed. It is true that the operation scar was smaller, and the length of hospital stay was shorter. But it was not true that off-pump CABG was as good as on-pump CABG.
The latest study, reported in New England Journal of Medicine, 5th Nov 2009, again added to the growing body of evidence. Dr L Shroyer and colleagues studied 2,203 patients who underwent bypass surgery ( half had the CABG on pump and was compared to the other half who received CABG off pump. The study is called ROOBY ( Randomised on / off bypass ) study. Aftre 1 year follow up, they found that there was no difference in cerebral cognitive impairment between the two groups and also that those who receive the off-pimp technique, tend to have fewer graft ( because it was more technically challenging to graft with a beating heart ) and after 1 year, more of the grafts in the off-pump group were occluded, compared to those done on-pump. To be exact, at angiography at 1 year, 87.8% of the grafts in the on-pump group were patent, compared to 82.6% in the off pump group. Also, at one year 36.5% of the grafts in the off pump group were occluded compared with 28.7% in the on-pump group.
This is not at all surprising as sowing on a beating heart is also less exact, and tended to be associated with pooere graft placement, and so more re-occlusion.
Well one thing is for sure, working on a non-beating heart ( on-pump) allows better control and more precise surgery ( that makes sense ) and working on a beating heart makes surgery less precise, with all the attendant problems.
As a spinoff from this tudy ( I cannot resist saying this ), it is good to know that at 1 year angiographic follow-up, 28% of grafts are blocked. As an interventionist, we always tell our patients that angioplasty is associated with the problem of restenosis, which can occur in 20% of our patients post PTCA, and with the use of Drug Eluting Stents, restenosis occurs in less than 5%. We are not doing so badly after all. CABG also has restenosis ( not so often stated ), in the first year. That is another issue to be dealt with another day.

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