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Patients who have cobalt-containing hip replacements may be at increased risk of heart disease, according to new research by the University of Strathclyde.
The research, which was funded by Heart Research UK, demonstrated that cobalt, even at low levels, can reduce heart contraction, making the heart less efficient at pumping blood around the body.
Over time, levels of cobalt in the bloodstream will rise, and the metal can accumulate in various organs of the body, including the heart. If left untreated, this could lead to heart failure and death.
Dr Susan Currie, who led the research, is now urging researchers to focus on new treatments to reduce or prevent the toxic effects of cobalt in patients with hip replacements.
What is the problem with cobalt-containing hip replacements?
Cobalt-containing hip replacements are often referred to as metal-on-metal (MoM) hip replacements as they have a metal ‘ball’ as well as a metal ‘cup’.
These MoM hip replacements, however, wear down more quickly in some patients than other types of hip placement. When the metal wears down, tiny amounts of cobalt are leaked into the blood stream.
In the late 2000s, surgeons began to voice concerns about the effects this could have on patients, and now, every patient with a MoM hip replacement (whom there are around 71,000 of in the UK), has an annual blood or MRI check to monitor the levels of metal ions in the blood.
Evidence which suggests these patients may be at greater risk of heart disease has been mounting over recent years, however, this study is the first to establish a link between cobalt-induced changes in calcium levels in heart muscle cells and reduced contraction of the heart.
Cobalt has a negative effect on calcium levels within heart cells
The researchers analysed blood samples from 30 people with cobalt-containing hip replacements in order to identify the level of cobalt in their blood.
They then used a highly sensitive form of ultrasound called global longitudinal strain to assess the heart health of 16 of these patients, as well as eight healthy controls.
Assessing the patients in this way allowed the researchers to identify patients with an abnormal contractile function, something that would not have been picked up with a routine check.
The researchers also measured the impact of cobalt across a range of experimental settings, including its effects on two types of heart cells and on cardiovascular function in both a laboratory model and humans.
The research demonstrated that cobalt, even at low levels, can reduce heart contraction, making the heart less efficient at pumping blood around the body. Calcium plays a key role in regulating heart contraction and it is thought that the effects of cobalt on CaMKII and calcium levels within the heart cells contributes to this reduction in contraction.
The results from the study highlight the potential for both early intervention and prevention of damaging effects of cobalt in the heart.
Cobalt-containing hip replacements now rarely used
Dr Currie said: “Hip replacements are the current treatment for advanced cases of arthritis. However, there is now very strong evidence of a link between hip replacements where metals such as cobalt and chromium are used in the artificial joint bearings, and the possibility of developing heart complications.”
“Our findings confirm a mechanism by which cobalt can negatively impact heart function. This has significant implications in terms of care for people who have received hip replacements which contain cobalt and who therefore may be at increased risk for the development of longer-term cardiac complications,” she concluded.
However, this type of implant is rarely used now, and Currie says only a small proportion of patients with this type of hip replacement are likely to be at risk.