It depends on the ECG machine. I've used many machines with these electrodes. The tab connector is a crocodile clip. **broken link removed**
OP one very basic thing that may give some improvement along with adequately shielded cables that are kept as short as feasibly possible is skin prep. A good rub of the electrode sites with isopropyl alcohol will lower skin impedance and lessen interference artifact. Adequate skin prep was the first thing drilled into me in college.