The farther apart they are, the slower the heartbeat. In the PAC strip, above, the second cardiac cycle is abnormal. Such a spot is called an ectopic focus, singular, or foci, plural. They are so large because the ventricles are so large. Ventricular tachycardia, above, is a precursor to v fib.
V fib is ineffective, disorganized ventricular beating that is incompatible with life.
You can also follow and diagnose an MI by utilizing cardiac enzymes. If there is still heart pain, the level will continue to rise until there is no more heart pain. By 36 hours post-MI, the LD1 peaks and by 72 hours, the SGOT peaks. Troponin peaks sooner than CK-MB and is being used as a marker in coronary care. This is called a 12-lead EKG, as there are 12 different electrical leads of information.