Posted: April 1st, 2011 | Filed under: Heart Health Education Resources | Tags: ECG, ECG recorders, Portable ECG Machine, Portable EKG Machine |
The P Wave P waves are caused by atrial depolarization. In normal sinus rhythm, the SA node acts as the pacemaker. The electrical impulse from the SA node spreads over the right and left atria to cause atrial depolarization. The P wave contour is usually smooth, entirely positive and of uniform size. The P wave duration is normally less than 0.12 sec and the amplitude is normally less than 0.25 mV. A negative P-wave can indicate depolarization arising from the AV node.
Note that the P wave corresponds to electrical impulses not mechanical atria contraction. Atrial contraction begins at about the middle of the P wave and continues during the PR segment. The PR Segment PR segment is the portion on the ECG wave from the end of the P wave to the beginning of the QRS complex, lasting about 0.1 seconds. The PR segment corresponds to the time between the end of atrial depolarization to the onset of ventricular depolarization. The PR segment is an isoelectric segment, that is, no wave or deflection is recorded. During the PR segment, the impulse travels from the AV node through the conducting tissue (bundle branches, and Purkinje fibers) towards the ventricles. Most of the delay in the PR segment occurs in the AV node. Although the PR segment is isoelectric, the atrial are actually contracting, filling the ventricles before ventricular systole.
The QRS Complex In normal sinus rhythm, each P wave is followed by a QRS complex. The QRS complex represents the time it takes for depolarization of the ventricles. The Q wave is not always present. The R wave is the point when half of the ventricular myocardium has been depolarized. The normal QRS duration range is from 0.04 sec to 0.12 sec measured from the initial deflection of the QRS from the isoelectric line to the end of the QRS complex.
Normal ventricular depolarization requires normal function of the right and left bundle branches. A block in either the right or left bundle branch delays depolarization of the ventricles, resulting in a prolonged QRS duration.
The ST Segment The ST segment represents the period from the end of ventricular depolarization to the beginning of ventricular repolarization. The ST segment lies between the end of the QRS complex and the initial deflection of the T-wave and is normally isoelectric. Although the ST segment is isoelectric, the ventricules are actually contracting.
The T Wave The T wave corresponds to the rapid ventricular repolarization. The wave is normally rounded and positive.
Posted: December 19th, 2009 | Filed under: Sudden Cardiac Death | Tags: arrhythmias, ECG, ECG recorders, Sudden Cardiac Death |
What is sudden cardiac death?
Sudden cardiac death (also called sudden arrest) is death resulting from an abrupt loss of heart function (cardiac arrest). The victim may or may not have diagnosed heart disease. The time and mode of death are unexpected. It occurs within minutes after symptoms appear. The most common underlying reason for patients to die suddenly from cardiac arrest is coronary heart disease (fatty buildups in the arteries that supply blood to the heart muscle).
What causes sudden cardiac death?
All known heart diseases can lead to cardiac arrest and sudden cardiac death. Most of the cardiac arrests that lead to sudden death occur when the electrical impulses in the diseased heart become rapid
(ventricular tachycardia) or chaotic (ventricular fibrillation) or both. This irregular heart rhythm (arrhythmia) causes the heart to suddenly stop beating. Some cardiac arrests are due to extreme slowing of the heart. This is called bradycardia.
In 90 percent of adult victims of sudden cardiac death, two or more major coronary arteries are narrowed by fatty buildups. Scarring from a prior heart attack is found in two-thirds of victims. When sudden death occurs in young adults, other heart abnormalities are more likely causes. Adrenaline released during intense physical or athletic activity often acts as a trigger for sudden death when these abnormalities are present. Under certain conditions, various heart medications and other drugs — as well as illegal drug abuse — can lead to abnormal heart rhythms that cause sudden death.
The term “massive heart attack” is often wrongly used in the media to describe sudden death. The term “heart attack” refers to death of heart muscle tissue due to the loss of blood supply, not necessarily resulting in a cardiac arrest or the death of the heart attack victim. A heart attack may cause cardiac arrest and sudden cardiac death, but the terms aren’t synonymous.
Can the cardiac arrest that causes sudden death be reversed?
Brain death and permanent death start to occur in just four to six minutes after someone experiences cardiac arrest. Cardiac arrest is reversible in most victims if it’s treated within a few minutes with an electric shock to the heart to restore a normal heartbeat. This process is called defibrillation. A victim’s chances of survival are reduced by 7 to 10 percent with every minute that passes without CPR and defibrillation. CPR can double or triple a cardiac arrest victim’s chances of survival. Few attempts at resuscitation succeed after 10 minutes. If someone becomes unconscious, call 9-1-1 immediately. They may be suffering from sudden cardiac arrest.
What are treatments for survivors?
If a cardiac arrest was due to ventricular tachycardia or ventricular fibrillation, survivors are at risk for another arrest, especially if they have underlying heart disease.
Survivors of cardiac arrest must have all causes corrected to prevent future episodes. Possible causes include myocardial ischemia (inadequate blood flow to the heart muscle), arrhythmia (abnormal heart rhythm), etc.
Possible tests and treatments include
- cardiac catheterization
- electrophysiologic tests
- coronary artery bypass surgery
- balloon angioplasty or PCI (PTCA)
- antiarrhythmic medicine
- implantable cardioverter / defibrillator
- implantable pacemaker
- heart transplant.
Source: American Heart Association
Posted: December 17th, 2009 | Filed under: ECG recorders | Tags: arrhythmias, ECG recorders |
ECG recorders are ambulatory devices which can be divided into two broad categories – continuous and event.
Continuous recorders, commonly known as Holter recorders, typically operate for 24 or 48 hours and are used to investigate suspected occasional arrhythmia which has not been detected during a shorter recording. Some recorders can be worn for up to
seven days. Holter recorders usually include a patient-operated button that timestamps the recording so that arrhythmias can be associated with symptoms during analysis of the complete recording.
Event recorders are for patients who experience symptoms very infrequently and require monitoring over longer periods. Continuous recording for extended periods would produce excessive data, thereby placing an undue storage and data
processing burden on the device and its ECG analysis system. By using intermittent recording techniques, the data storage and report processing burden is reduced.
Patient-activated ECG event recorders are devices that allow patients to initiate an ECG recording when they experience symptoms of arrhythmia, such as palpitations, light-headedness or syncope (partial or complete loss of consciousness).
Traditionally, patients undergoing investigation would be monitored via a recorder with ECG cable and electrodes.
However, advancements in technology have led to the development of post-event recorders with integrated chest and/or finger electrodes. These devices allow patients to make post-event recordings without the discomfort of long-term connection to an ECG cable, eg restrictions on bathing and irritation of the skin.
