Some patients will still require another procedure due to either progression of the disease or degeneration of the graft vessel. By Michael Lim
DOES undergoing a heart bypass surgery mean the end of heart problems? With rising affluence and increasing longevity, heart disease becomes an increasingly important cause of disability and death in the older adults.
Despite significant advances in the development of non-invasive techniques, such as the opening of the heart arteries with small millimetre-sized cylindrical metallic meshes (technique is also termed as stenting), there remains a segment of those with severe heart artery disease which will require coronary artery bypass graft surgery (CABG) or open heart bypass surgery.
What is less well known is the subsequent outcomes for these elderly patients following CABG. This fortnight, a large United States database study, the Society of Thoracic Surgeons’ national experience 1991-2007, published in the Circulation journal reported on the outcomes of older adults who underwent CABG. The study team, led by researchers from Duke Clinical Research Institute, looked at the database of more than 700,000 patients of age 65 years or more who underwent first-time isolated CABG from 1991 to 2007.
It is a common assumption by many patients that undergoing a CABG will solve their heart problems and they will not need to worry about heart disease again. The reality is that some will still require another procedure after the CABG due to either progression of the disease in the native heart arteries or degeneration of the graft vessel resulting in subsequent blockage of the graft vessel.
The study showed that for the elderly, the need for a repeat CABG or stenting was low with a cumulative incidence of 13 per cent, and 16 per cent at 10 and 18 years after CABG, respectively.
For those who developed disease of the native arteries or grafts after CABG, stenting remained the preferred choice. More than 90 per cent of those who had repeat procedures underwent stenting, and repeat CABG was very low with a cumulative incidence of only 1.7 per cent at 18 years.
Generally, younger patients were more likely to undergo repeat procedures than older patients. For the youngest age group of patients in this study (65 to 69 years old), the repeat procedure rate at 18 years was 30 per cent, as compared to 11 per cent for those in their 80s. Possible reasons could be that the older group was less active and less likely to be symptomatic, and physicians may be less willing to perform procedures in the more elderly patients.
Possible reasons as to why the likelihood of a second procedure was relatively low were the increased use of arterial grafts and the near-universal usage of cholesterol-lowering drugs in the patients. Arterial grafts especially from the internal mammary arteries (arteries behind the breast bone) are much longer lasting than the vein grafts taken from the legs and have become routinely used in CABG.
Is heart disease survival better or worse than cancer?
Most patients tend to take the news of developing cancer with fear and trepidation as they expect a much shorter lifespan. However, news of heart disease is often received with calmness and little anxiety. Therefore, it may come as a surprise that for those 65 years and above, even after CABG , only one in five are still alive after 18 years. For those who have had CABG, heart disease accounts for about half of the eventual causes of death. Hence, the low 20 per cent survival rate after CABG in this older adult population may be even worse than getting early stage cancer.
The presence of disease of the left main artery (main heart artery supplying the left main pumping chamber), poor heart function, diabetes, multiple vessel disease and kidney disease have a negative impact on long-term survival after CABG. One of the most important factors for reduced hospital death and better long-term survival is the use of the internal mammary artery graft (IMA graft). Studies have shown that 10 years after CABG, nine in 10 IMA grafts still remain patent.
Research studies have shown that poor control of risk factors, such as high blood pressure, diabetes mellitus, high cholesterol and smoking, are closely related to subsequent blockage of the CABG graft vessels. The honeymoon period passes after the first five years, and between five to 10 years after CABG, problems start to arise, often coinciding with the gradual blockage of vein grafts. The data varies but 10 years after CABG about 40 to 60 per cent of the vein grafts are blocked. As heart disease accounts for about half of the eventual causes of death in those who have had CABG, patients should have regular follow-up and careful assessment to look for evidence of blockage of the grafts, especially after the first five years.
Loss of benefit
A meta-analysis based on individual patient data from all of the available randomised studies showed that survival in those undergoing CABG, as compared to those on medical treatment, improved gradually over the first five to seven years.
This survival benefit of CABG over medical treatment gradually diminishes and, at about the 10 to 12 year follow-up period, this survival benefit of CABG will approximate that of medical treatment. This may be due to a multitude of reasons, including the reduced life expectancy of heart disease patients regardless of treatment choice, and the likelihood of a second procedure after CABG with resultant increase in deaths from subsequent procedures. Another reason that affects the data analysis is that those high-risk patients on medical treatment may eventually undergo CABG, leaving those remaining in the medical treatment group who have better survival characteristics.
What all this means for the older adults who undergo CABG is that the use of the IMA graft during CABG, strict control of risk factors, such as high blood pressure, diabetes, high cholesterol and smoking cessation after CABG, regular assessment of the patency of the graft after five years, and intervening appropriately by stenting to keep the grafts and native artery segments patent can potentially reduce the death resulting from progressive heart disease and hence prolong survival.