Tuesday, July 31, 2007
- P wave: the sequential activation (depolarization) of the right and left atria
- QRS complex: right and left ventricular depolarization (normally the ventricles are activated simultaneously)
- ST-T wave: ventricular repolarization
- U wave: origin for this wave is not clear - but probably represents "afterdepolarizations" in the ventricles
- PR interval: time interval from onset of atrial depolarization (P wave) to onset of ventricular depolarization (QRS complex)
- QRS duration: duration of ventricular muscle depolarization
- QT interval: duration of ventricular depolarization and repolarization
- RR interval: duration of ventricular cardiac cycle (an indicator of ventricular rate)
- PP interval: duration of atrial cycle (an indicator of atrial rate)
Labels: ECG Waves and Intervals
The standard 12-lead electrocardiogram is a representation of the heart's electrical activity recorded from electrodes on the body surface.
Labels: The standard 12 Lead Electrocardiogram
Sunday, July 29, 2007
A typical electrocardiograph runs at a paper speed of 25 mm/s, although faster paper speeds are occasionally used. Each small block of ECG paper is 1 mm2. At a paper speed of 25 mm/s, one small block of ECG paper translates into 0.04 s (or 40 ms). Five small blocks make up 1 large block, which translates into 0.20 s (or 200 ms). Hence, there are 5 large blocks per second. A diagnostic quality 12 lead ECG is calibrated at 10 mm/mV, so 1 mm translates into 0.1 mV.Labels: ECG Graph Paper
Kindly go through this animation. It gives a very good idea of the cardiac electronic vector and the recording of the ECG.
http://en.wikipedia.org/wiki/Image:ECG_principle_slow.gif
http://en.wikipedia.org/wiki/Image:ECG_principle_slow.gif
Labels: Animation
A machine or device used to record an electrocardiogram, also known as an EKG or ECG. The ECG recorded by the electrocardiograph translates the electrical impulses generated in the heart into wave-like signals that is recorded on paper, and used to diagnose many conditions of the heart. Many heart conditions have characteristic ECG’s that aid the physician in making a diagnosis or directing care.
Labels: Electrocardiograph
Tuesday, July 24, 2007
The heart is an organ responsible for pumping the blood in the body. Through the blood, nutrients are provided to the body's cells and waste products are removed from these cells. The heart has four chambers: two upper chambers which are called atria and two lower chambers which are called ventricles. These chambers are also classified as left and right atrium and left and right ventricle, and each of them has a specific function.
The heart pumps the blood by repeated contractions of its muscles. These cardiac contractions are produced due to an electrical phenomenon called depolarization, that takes place in the heart muscles' cells (myocardial cells). The myocardial cells have a negative electric resting potential. Through the depolarization, this potential goes temporarily to a positive value that stimulates them to contract. Each heart cycle consists of two phases: depolarization, which represents the myocardial stimulation and repolarization, which represents the recovery phase. Both depolarization and repolarization are electrical phenomena.
Specialized conductive fibers inside the myocardium allow the transmission of cardiac stimulus to all the myocardial cells in a specific order. The atria contract first, and then the ventricles. Under normal conditions, the cardiac stimulus originates in a point, called sinoatrial node or sinus node, located in the posterior wall of the right atrium. The property of the node's cells to fire automaticaly and periodically an electric stimulus is called automaticity. However, the automaticity is a property posessed by all myocardial cells. In case the sinoatrial node fails to fire a stimulus, other myocardial cells will initiate this stimulation automatically.
wave produces a current wave of atrial contraction, which is called the P wave, as presented in the following figure. After a puse of about 1/10 of a second, the atrial depolarization wave reaches the atrioventricular node, which is situated between the two sets of chambers. The electrical stimulus passes then from the atrioventricular node through the bundle of His to the atrioventricular bundle branches, and the Purkinje fibers, which initiate the ventricular depolarization.
The ventricular depolarization is represented graphically on the electrocardiogram by an abrupt waveform called QRS complex, as presented in the following figure. During the ventricular depolarization, the right and
The ventricular depolarization is represented graphically on the electrocardiogram by an abrupt waveform called QRS complex, as presented in the following figure. During the ventricular depolarization, the right and
left ventricles contracts and pump the blood they contain. The QRS complex consists of three distinctive waves: Q, R and S. After the QRS complex, there is a pause, called ST segment. During the ventricular repolarization, which is represented by the T wave, the heart cells regain the negative polarization.
The sinoatrial node stimulates the heart at a rate of 60-80 beats per minute. If the sinoatrial node fails to fire an impulse, other cells from atria can do that instead. If this does not happen, then the artioventricular node can fire impulses at a rate of about 40-60 times per minute. Further, if no excitation occurs from the previous sources, the ventricular cells can fire a depolarization at a rate of about 20-40 times per minute.
The sinoatrial node stimulates the heart at a rate of 60-80 beats per minute. If the sinoatrial node fails to fire an impulse, other cells from atria can do that instead. If this does not happen, then the artioventricular node can fire impulses at a rate of about 40-60 times per minute. Further, if no excitation occurs from the previous sources, the ventricular cells can fire a depolarization at a rate of about 20-40 times per minute.
ECG lecture
Theoretical Basis of the ECG:
An electrical current in the direction towards the positive end of a bipolar electrode causes a positive deflection of the stylus of the ECG. If the number of myocardial cells (dipoles) in this direction increases, the current will increase as well. The greater the current, the more positive the voltage. An electrical current in the direction away from the positive end of a bipolar electrode causes a negative deflection of the stylus of the ECG. If the number of myocardial cells (dipoles) in this direction increases, the current will increase as well. The greater the current, the more negative the voltage.
ECG Leads:
An electrocardiographic lead is a recording electrode or a pair of recording electrodes at a specified location. In clinical practice, twelve leads are usually used in the diagnostic ECG, although there is no limitation to the number of leads one may select for special purposes. The leads are usually placed on the elbows and stifles. A right leg electrode is used as the ground.
ECG Standard Leads:
Leads I, II and III are all bipolar (i.e., they detect a change in electric potential between two points) and detect an electrical potential change in the frontal plane. Lead I is between the right arm and left arm electrodes, the left arm being positive. Lead II is between the right arm and left leg electrodes, the left leg being positive. Lead III is between the left arm and left leg electrodes, the left leg again being positive.
Sometimes, the acronym EKG is used instead of ECG.
Labels: ECG introduction
The lecture will introduce:
- The use of differential amplifier
- How the syllabus is framed
- How the ECG will help
- What is the function and types of the ECG machine ?
Labels: ECG lecture
