higher detection sensitivity the voltage waveform can be sampled in sychronization with the heart rate or the average voltage removed and only the change amplified such methods are referred to as u201c ac coupling u201d a further refinement to reduce the electrical noise is to pass the signal through a digital band pass filter having a center frequency tracking the heart rate to avoid any potential tissue damage the temperature of the elements 10 of the mesh 7 is only slightly above the blood temperature typically 0 1 3 degrees c above blood temperature fig3 a shows the mesh 7 in a compressed configuration u201c a u201d and fig3 b shows the mesh 7 in an expanded configuration u201c b u201d since the mesh 7 has to fit into a catheter 60 the mesh 7 should be very flexible besides elements 10 discussed earlier there is also a large number of leads 13 coming out of the mesh 7 leads 13 can be loose as shown in fig3 b or may be bonded to the mesh 7 to avoid feeding a large number of wires all the way to an operating console an electronic selector switch may be employed which may for example be mounted in the catheter 60 this reduces the number of electrical wires from over 100 to about 10 the mesh 7 can be self expanding elastic or balloon expandable self expanding allows normal blood flow during the procedure for balloon expandable devices the expansion balloon should be removed before the mapping to avoid blocking the flow of blood fig4 shows the mesh 7 in more detail insulated longitudinal i e parallel to catheter wires 25 are crossed by cross wires 26 each section of the mesh 7 is.