A simple description of heart action leading to ECG interpretation
In simplest terms, a heart is a blood pump, consisting of two chambers, atrium (smaller, first along the blood stream), and ventricle (larger, second along the blood stream). These two chambers are connected by a wall that includes a valve which only opens in the direction of the blood stream, and it shuts when the blood would want to flow the other way.
By initial contraction of the atrium, blood flows through the open valve to the ventricle. The second contraction normally takes place after the ventricle has already filled with blood from the atrium. The contraction of the ventricle shuts the valve and sends blood into the body.
Heart electric signals, normal and arrhythmic
ECG electric signals follow this repeated pattern of contractions, from atrial to ventricular. Electric pulse-wise, there is a "sinus node" in the atria where the electric pulse originates and is responsible for the "pace making". Further down the heart there is a mid-section between the atrium and the ventricle which is called atrioventricular (AV) node. This node delays the electric pulse so there can be a delay between the atrium contraction pulse and the ventricle contaction pulse.
Changes in electric signals from the normal rhythm seen through electrocardiography are most frequently a sign of problems in the heart although they can be benign too. The most frequently found deviations from the normal heart beat signals, or heart arrhythmias, are listed below and are included as test pulses with all ECG simulators.
The term tachycardia is used for faster heart beat, while bradycardia is used for slower than normal heart beat.
Likewise, the term ventricular arrhythmias stands for abnormal pulses that originate inside the ventricle, while all other abnormalities are termed supraventricular arrhythmias.
List of repeated ECG patterns
Normal heart beat: ECG simulators will typically have two options, pediatric normal heart beat, at about 40 beats a minute, and an adult heart beat, at around 80 beats per minute. Either one of these will represent a normal ECG reading.
Arrhythmias originating in the atria
Sinus Arrhythmia: Faster beating of the "pace maker", sinus node in the atrium, causing the entire heart to beat faster. This can be quite normal, such as during exercise.
Asystole: Complete absence of any electric signals in the heart. Flatline EKG reading.
Missed beat: Self explanatory. Heart acts normally, misses a beat, and returns to normal action.
Bigeminy: Abnormal pulse appears every other heart beat.
Trigeminy: Abnormal pulse appears every third heart beat.
SVT: Supraventricular tachycardia, happens when either the atrium or the AV node starts firing faster and regularly.
PAC or APC: Premature atrial contractions, or premature supraventricular contractions. Abnormality when the atria contract earlier than normal.
Sick Sinus Syndrome: Happens when sinus node reduces the expected heart rate.
Atrial flutter: Similar to atrial fibrillation but signal originating in a single part of the atria. The frequency can be as fast as three hundred contractions per minute, but the AV will only allow every other beat through, so the ventricular contractions will be exactly one half.
Atrial fibrillation: Stands for electric signals originated from multiple different places in the atria. Fibrillation will cause faster than normal heart beat. Atrial fibrillation can be either coarse or fine.
PVC: Premature ventricular complex, electric signal starts in the ventricle and causes ventricle to beat earlier than normal. This is usually not repeated, but a single event. This can have a focus on either ventricle, left or right, or can be multi focal. PVC can come as single aberration, or in pairs, etc. They are different from Bigeminy or Trigeminy above.
Ventricular fibrillation: Faster and irregular beating of the ventricle. Fibrillation can either be fine or coarse. The fibrillation causes the heart to become unable to beat or pump any appreciable amount of blood through the body. This is termed cardiac arrest, or stoppage of the heart.
Ventricular tachychardia: Faster beating of the ventricle, usually quite regular. A very dangerous symptom.
First, second, and third degree AV blocks: Happen when the AV node transfers the electric signal to the ventricules slower than normal, causing the delay in ventricular contractions.
Bundle branch blocks: Happens when the electric signal is stopped on its way through the ventricule, causing prolongation of the ventricular action.
These are the ECG interpretation types of the most commonly simulated ECG rhythms. Check out ECG Simulators for info on the actual ECG simulators. Also, see section on ACLS simulator to find out how you can do ECG interpretation practice, simulate the ECG monitor, and learn to perform proper action in case of a patient who may be experiencing a heart arrest. The simulation presented there contains a "on the job" ECG interpretation quiz.