ELECTROCARDIOGRAM -ELECTRICAL ACTIVATION OF HEART

ELECTROCARDIOGRAM -ELECTRICAL ACTIVATION OF HEART

The central function of the heart is to contract rhythmically and pump blood to the lungs for oxygenation and then to pump this oxygen-enriched blood into the systemic circulation. The signal for cardiac contraction is the spread of electrical currents through the heart muscle. These currents are produced by pacemaker cells this property is known as automaticity. In our conduction system of the heart, there are various specialized cells are present. In which the SA node is known as the pacemaker of the heart. The signal for heartbeat initiation starts in the sinus node. This node is located in the right atrium near the opening of the superior vena cava. The initiation of cardiac contraction by electrical stimulation is known as electromechanical coupling. Akey part of this mechanism is the release of the calcium ions inside the atrial and ventricular heart muscle cells .This process links electrical and mechanical activation. The Electrocardiogram is capable of recording only relatively large current produced by the mass of working heart muscle. The much smaller amplitude signals generated by the sinus node and AV node are invisible with clinical recordings. Depolarization of the His bundle area can only be recorded from inside the heart during specialized cardiac EP procedures. The more technical term for the cardiac activation process is depolarization. The return of the heart muscle cell to their resting state is following stimulation is called repolarization. These key terms are derived from the fact that normal resting cardiac cells are polarized; that is, they carry electrical charges on their surface.

Electrocardiogram

The figure shows that the resting heart muscle cell is polarized, that is it carries an electrical charge. Outside of the cell is positively charged and inside of the cell is negatively charged.

cardiac electrophysiology

When the cell is stimulated it begins to depolarize notice the stippled area, Inside of the cell becomes positive and outside becomes negative. The path of depolarization is represented with an arrow

Add caption
Consequently, a small electrical current is formed that spreads along the length of the cell as stimulation and depolarization occur until the entire cell is depolarized.


Repolarization occurs when the stimulated cell returns to the resting state. The directions of depolarization and repolarization are represented by arrows. Depolarization of the atria produces the P wave on the electrocardiogram, whereas depolarization of the ventricles produces the QRS complex. Repolarization of the ventricles produces the ST-T complex, U wave. Atrial repolarization is usually obscured by ventricular potentials. Atrial ST-segment and atrial T wave are generally not observed on the routine ECG because of their low amplitudes.


For individual myocardial fibres depolarization and repolarization proceed in the same direction. However, for entire myocardium, depolarization proceeds in the opposite direction from the innermost layer to the outermost layer that is from endocardium to epicardium. The exact mechanisms of this asymmetry are not fully understood. The ECG records the electrical activity of a large mass of atrial and ventricular cells, not of just a single cell, Because of cardiac depolarization and repolarization normally occur in a synchronized fashion, The ECG can record these electrical currents as specific waveforms.

You can also refer this topic in the following link:https://www.youtube.com/channel/UCRrYRylZdS67_kbATQrLQqA


Comments

Post a Comment

Popular posts from this blog

PERICARDITIS ECG CHANGES - HEART AND TECHY

Image
  PERICARDITIS ECG CHANGES-HEART AND TECHY P ericarditis  is the  inflammation  of pericardium. Pericarditis Acute pericarditis is  caused  by  infective , autoimmune,neoplastic,  radiation injury  or  metabolic causes. Virus Viral infection  is the most common  cause  of pericarditis.Pericarditis in  acute myocardial infarction  is  due  to local pericardial inflammation. Main   ecg   changes  in pericardial effusion are PR  segment depression  and ST segment  elevation virus ST segment elevation is occur  due   to change  in  epicardium,this  exerts a  pressure  in our  heart  which will  result in   decreasing  contractility,decrease filling and  decrease   cardiac output. Our  heart  consist of  3  layers, epicardium myocardium and  endocardium,epicardium  is the layer which is very close to pericardium,so  changes  which occur in  epicardium  in pericarditis will also a ffect   pericardium layers of the heart Majority  of perfusion occur in our  heart  during diastole.C hanges  in
Read more

RIGHT VENTRICULAR FUNCTION ASSESSMENT IN ECHOCARDIOGRAPHY-RIGHT VENTRICULAR SERIES PART-2

Image
 RIGHT VENTRICULAR SERIES PART-2  RIGHT VENTRICULAR FUNCTION ASSESSMENT Why should we  measure   Right Ventricular   function  in the  echo? The right ventricle  has its  unique function  In our  first   part of  Right Ventricular series(RV SERIES) we  discussed  how to quantify  Right Ventricular size  in  echo Before going  to the lecture  we have  to know  there is some  limitation  for assessing Right Ventricle in  echo  because of the  crescentic shape , we had already  discussed  this in our  first   part of  RV series. Right ventricular function is mainly assessed by  5   methods: Tricuspid  annular plane   systolic excursion fractional area  change tei index s   prime visual  estimation  of RV  free wall  tricuspid  annular motion TAPSE   TAPSE is  measured  from Right Ventricle m mode. In  apical  four-chamber view m mode cursor  placed  on the  junction  of  tricuspid valve plane  with the RV  free wall.  Tapse is the  difference  in displacement during  diastole  and  systol
Read more

HEART AND TECHY-RIGHT VENTRICULAR SIZE AND FUNCTION ASSESSMENT ECHO-PART 1

Image
RIGHT VENTRICLE SIZE AND FUNCTION IN ECHOCARDIOGRAPHY The right  ventricle   is a  complex   three-dimensional shape.  Echocardiographic assessment of the  right ventricle  is  more   difficult  than that of left ventricle because of the  complex geometry  and is  divided   into two   parts : the inflow tract and the outflow tract,  separated  by the crista supraventricular. Echocardiographic  imaging of  RV  function and  measurement  of ejection fraction has been  difficult  because of the  complex form  and  motion pattern  of the  RV  and  problems  with defining the  endocardial surface  of the  thin  RV  free wall.  Another important factor that complicates the interpretation of RV  function  is the varying  loading conditions.  In daily cardiology practice, RV function has traditionally been  evaluated  qualitatively by  2D  echocardiography. QUALITATIVE PARAMETERS TO ASSESS THE RV SIZE IN ECHOCARDIOGRAPHY: A standard apical four-chamber is best to assess RV size compared with t
Read more