A 鈥渨ire鈥� made from a patient鈥檚 own cells could one day be used to keep electrical impulses flowing in the heart. It may even mean people will no longer have to be fitted with pacemakers.
A normal heart has an efficient electrical circuit that sychronises the beats of the atria and ventricles 鈥� the chambers of the heart 鈥� so that they pump blood effectively. Impulses are produced by the heart鈥檚 natural pacemaker, a cluster of cells called the sino-atrial node, situated in the right atrium. These are then relayed to the ventricles via the atrioventricular (AV) node.
In some people the AV node fails to conduct these impulses, preventing the signal reaching the ventricular muscle 鈥� a condition known as complete heart block. This disrupts the heart鈥檚 rhythm, and can lead to heart failure.
Advertisement
鈥淥ne in 22,000 people is born with complete heart block,鈥� says Douglas Cowan of the Children鈥檚 Hospital Boston, where the new technique has been developed. Children treated for other congenital heart defects, such as transposed 鈥� or wrongly connected 鈥� arteries, can also develop the condition, as the AV node is easily damaged during surgery. 鈥淭he AV node鈥檚 conductive tissue is so small, a stray suture alone can cause this,鈥� says Cowan.
At the moment, the only solution for someone with complete heart block is to fit a pacemaker, which artificially regulates the heartbeat via electrodes connected to the heart. Fitting pacemakers to children is problematic, as the electrodes can damage tiny hearts and create blood clots. Now Cowan and colleagues have grown and implanted tissue in rats that can bypass a faulty AV node. It can be produced from the patient鈥檚 own cells, which stops it from being rejected by the body.
The Boston team harvested skeletal muscle cells from several rats and isolated muscle precursor cells called myoblasts from each sample. The researchers grew these cells on a collagen scaffold coated in a nutrient medium to create a piece of muscle tissue with the cells oriented along the scaffold. The engineered tissue can carry a current because proteins called connexins, which are produced by the muscle cells, allow ions to flow from cell to cell.
The team then implanted a 2 millimetre by 2 millimetre slice of the scaffold into the hearts of each rat. The tissue was stitched into a groove next to the AV node, which was functioning normally. By injecting a chemical into the tissue that glows when a current passes through it, the team were able to ascertain that the implant was carrying current, and did so for the rest of each rat鈥檚 natural life 鈥� about three years. Effectively, the rats had a spare AV node working alongside their own.
鈥淥ur experiments prove the principle that engineered tissue constructs can function as electrical conduits and, ultimately, may offer a substitute treatment to conventional pacing therapy,鈥� the team report in the American Journal of Pathology (DOI: 10.2353/ajpath.2006.051163).
The Boston team鈥檚 next challenge will be to engineer their tissue implant so that like an AV node it introduces a small delay when relaying impulses between the atria and ventricles. 鈥淭he tissue must behave like a natural AV node in slowing conduction,鈥� says Nick Severs, a cell biologist at the National Heart and Lung Institute in London. 鈥淥therwise an excessively fast conduction pathway could lead to potentially dangerous disturbances of heart rhythm.鈥�
