The Electrocardiogram PDF

The Electrocardiogram DR PATRICIA DE GABRIELE MD DIP.WH(ICGP) FMCFD Intrinsic Conduction System of the Heart ▪ Cardiac muscle cells can & do contract ▪ Spontaneously & independently ▪ Regularly ▪ Continuously ▪ Cells in different areas of the heart have different rhythms. ▪ At...

The Electrocardiogram DR PATRICIA DE GABRIELE MD DIP.WH(ICGP) FMCFD Intrinsic Conduction System of the Heart ▪ Cardiac muscle cells can & do contract ▪ Spontaneously & independently ▪ Regularly ▪ Continuously ▪ Cells in different areas of the heart have different rhythms. ▪ Atrial cells – 60 contractions/min ▪ Ventricular cells – 20-40 contractions/min ▪ There is a unifying control system to make the heart pump efficiently. Regulation of Heart Activity ▪ There are 2 systems that regulate heart activity: 1. Nerves of the Autonomic Nervous System ▪ Slow down the heart rate – Parasympathetic Nerves ▪ Increase the heart rate – Sympathetic Nerves 2. Intrinsic Conduction System/Nodal System ▪ Sets the basic rhythm of the heart at about 75 beats/min ▪ Makes the heart depolarize in one direction only ▪ Made up of special tissue that makes up the conduction system of the heart The Electrocardiogram ▪ This is usually a 12-Lead ECG. ▪ A triangle with the heart at its centre (Einthoven’s triangle) can be drawn by placing electrodes ▪ on both arms – Leads I &II ▪ on the left leg – Lead III These are called the LIMB LEADS. ▪ There are 6 unipolar chest leads – V1 – V6 ▪ There are 3 unipolar augmented limb leads – aVR (right arm), aVL (left arm) and aVF (left foot). Position of ECG Leads The ECG The P wave is produced by atrial depolarisation. The QRS complex is produced by ventricular depolarisation. The ST segment and the T wave are produced by ventricular repolarisation. The U wave is believed to be due to slow repolarisation of the papillary muscles. It is an inconsistent finding. The PR interval represents atrial depolarisation and conduction through the AV node. It lasts for 0.12 – 0.20 second. The QRS duration represents ventricular depolarisation and atrial repolarisation. It lasts 0.10 second. The QT interval represents ventricular depolarisation plus ventricular repolarisation. It lasts up to 0.43 second.