vtec applied science unit one biology the ecg what's an ecg well it's an electrocardiogram is an ecg and what it does is it measures the action potentials of the heart so the electrical impulses which control the heart okay uh electro is electricity cardio is heart and gram means picture so it's a picture of the electrical signals in the heart as an ecg from gcse you should remember that the heart is in four sections you've got the atria which receive the blood uh from the body and from the lungs and then you've got the ventricles which pump the blood to the body and the lungs so the atria are the smaller ones at the top and then the ventricles are the more muscular ones at the bottom so they are the four chambers of the heart the atria the left and right atrium and then the left and right ventricle okay the four chambers of the heart now electrodes what you do is you place electrodes on the body uh over the chest and they detect these electrical impulses which are controlling the heart muscles okay and then a machine will amplify and record them and display them and then a clever doctor or nurse will look at it and possibly know if there's a problem with your heart by looking at this trace this is a typical trace and the different bits of it so there's the p wave and the p wave is when the atria contract remember that the atria are the smaller chambers at the top uh so when they contract when they squeeze the blood into the ventricles and this is called atrial systole yeah so the atria contract that's the p wave the bit in the middle which is a lot bigger is called the qrs complex and that's when the ventricles contract that is ventricular systole remember that the ventricles are a lot bigger so the signal is going to be a lot bigger and then lastly we have the t wave and that's when the ventricles repolarize okay and that is diastole that is when it recovers when it relaxes systole is when it contracts diastole is when it relaxes how do you remember all this well it's dead easy p q r s t basically if you know your alphabet shouldn't be that hard okay atria contract ventricles contract relax now what's interesting about the heart is that the beating of the heart is controlled by a small cluster of cells called the pacemaker so your brain doesn't have to tell your heart to beat it will beat all by itself if you cut somebody's heart out of their body then it will carry on beating for a while okay so this pacemaker produces an electrical impulse which causes the heart muscles to contract okay so the heart will beat all by itself thanks to this bunch of cells called the pacemaker remember p wave then the qrs complex then the t wave etc again and again hopefully so these are the questions you need to be able to do here is a normal ecg trace what produces this trace describe what is happening in the heart at each of the three sections what is a pacemaker and what is its function you