Cardiac Rhythms

Cardiac rhythm is the manner in which the heart beats as a result of electrical impulses. The sinus node is the starting point of the electrical impulse in the majority of rhythms; however this is not always the case. Heart rhythms vary from being regular to irregular to being threatening to the life of the individual.

Regular Rhythm

• A regular beating heart is universally known as a sinus rhythm. The beating of the heart is driven by the natural pacemaker, the sinus node. An impulse is transmitted from the SA node to the walls of the atria. It then reaches the atrioventricular (AV) node where a slight delay occurs; the bundle of His and Purkinje fiber of the left and right bundle branches conduct the impulse to the ventricular walls. Regular occurrence of this process and a heart rate of 60-100 beats per minute in adults is defined as sinus rhythm.

Abnormal Rhythms

• A beating heart can be abnormal rhythmically in a number of ways. An arrhythmia is the collective term for an abnormal cardiac rhythm. Five million people in North America get arrhythmias or are in a constant state of arrhythmia. The majority of these people are over the age of 50 or have an underlying heart condition. The most common abnormal cardiac rhythms are sinus bradycardia; a heart beat slower the 60 beats per minute, sinus tachycardia, a heart rate greater than 100 beats per minute and atrial fibrillation, which is a rhythm with chaotic generation of electrical impulses in the atria. Atrial fibrillation affects one percent of the population.

Causes of Arrhythmia

• Arrhythmias are commonly caused when problems arise in the sinus node. If the SA node fires impulses in an irregular manner the general rhythm of the heart will be affected; this can be linked to arrhythmias, such as atrial fibrillation. Problems with conduction pathways also cause arrhythmias. The bundle of His is a group of specialized conductive cells, if these or the bundle branches of the ventricles are sickly impulses will not travel in a regular manner and arrhythmias will arise, as well as other cardiac-related problems.

Symptoms Associated with Abnormal Rhythm

• Abnormal rhythms do not always cause symptoms, but if symptoms are to be experienced they are generally likely to be palpitations, dizziness and syncope. More specific symptoms may be seen in some conditions.

Determining Cardiac Rhythm

• The electrocardiogram (ECG) is the most efficient way in determining heart rhythm. It is also the easiest way to detect an arrhythmia. A 12-lead ECG is done by attaching an individual to an ECG machine via 10 electrodes. Six are placed in specific positions across the chest, these are the precordial leads and four on the limbs to produce the limb leads. A trace is then taken from the machine, charting the heart's electrical activity and thereby indicating the rhythm.