disturbance of heart rhythm to irregular heartbeat. It occurs in a physiological and pathological conditions. In arythmia, SA node may or may not be the pacemaker. Arythmias are divided into two types: i. normotopic arrhythmia in which the SA node is the pacemaker ii. Ectopic arrhythmic in which the structure of the heart other than SA node is the pacemaker
it is classified under three headings: i. sinus arrhythmia ii.sinus tachycardia iii.sinus bradycardia
Normal sinus rhythm refers to the normal heartbeat with the SA node as the pace maker. The heart beat on average is 72 beats / minute but it increases during expiration and decreases during inspiration. This is called sinus arrhythmia or respiratory sinus arrhythmia (RSA).
ECG is normal during sinus arrhythmia. Only the duration of the R-R interval varies rhythmically according to the phases of respiration.
Cause of sinus arrythimia
It is due to fluctuation in the discharge of impulses from SA node. During inspiration the interthoracic pressure decreases which inflates the lungs and increases the venous return.
the increase in the discharge of impulses from SA node is known as sinus tachycardia.
ECG Changes in Sinus tachycardia
The ECG is normal in sinus tachycardia except for the R-R intervals which are short because of increased heart rate. The discharge of impusles from the SA node is very rapid and the heart rate increases upto 100/minute and sometimes upto 150/minute
Conditions when sinus tachycardia takes place
it occurs in physiological and pathological conditions. The physiological conditions in which it occurs are exercise, emotion and pregnancy. Pathological conditions include: fever, anemia, hyperthyroidism, cardiomyopathy, valvular heart disease, hemorrhagic shock.
palpitations (sensation of feeling of the heartbeat), dizziness, fainting, shortness of breath, chest discomfort.
this is the reduction of discharges from the SA node. It is characterized by low heart rate around 40 per minute.
ECG Changes in sinus bradycardia
the ECG is normal but the R-R interval is prolonged.
Conditions in which sinus bradycardia occurs
sinus bradycardia also occurs under pathological and physiological conditions. Physiologically it occurs during sleep and in atheletes. Pathologically it occurs in diseases of SA node, hypothermia, hypothyroidism, heart rate, congenital heart disease, degernative process of aging, obstructive jaundice, increase intracranial pressure, artherosclerosis
Carotid sinus syndrome
bradycardia due to artherosclerosis of carotid artery at the region of the carotid sinus is called carotid sinus sysdrome.
Sick sinus syndrome
sick sinus syndrome is the common condition in sinus bradycardia is characterized by dizziness and unconsciousness.
fatigue, weakness, shortness of breath, lack of concentration, difficulty in exercising.
In ectopic arrhythmia, the structure of heart othe than the SA node is the pacemaker of the heart. Ectopic arrhythmia is further divided into two: hemotopic arrhythmia and hetertropic arrhythmia. The different ectopic arrhythmias are: Heart block, extrasystole, paroxysmal tachycardia, artial flutter, atrial fibrillation, ventricular fibrillation
the term heart block refers to the blockage of impulses generated by SA node in the conductive system. Because of the blockage, the impulses cannot reach the cardiac musculature causing the heart block. Based on the area affected, heart block can be divided into two: Sinuatrial block and atrioventricular block.
when the impulses from the SA node are not transmitted to the AV node because of defects in the intermodal fibers it causes a sinuatrial heart block. At this point the heart stops suddenly. After a few seconds, the Av node takes over as the pacemaker and the heart rate reduces. This is called AV node rhythm. This AV nodal rhythm can be divided in to upper, lower and middle nodal rhythms.
Upper AV nodal rhythm
when impulses are discharged from the upper part of the AV node it is refered to as upper nodal rhythm. The P wave in this case is inverted and the QRS complex and the T wave are normal.
Lower AV nodal rhythm
this is lead by impulses from the lower part of the AV node. This causes the impulses to reach the ventricles before the atria. As a result on the ECG, the QRS complex comes before the P wave and an RP interval is obtained instead or a PR interval.
Here the impulses are not transmitted from the atria to the ventricles due to a defective conduction system. Atrioventricular block can be divided into two: Incomplete heart block and completer heart block.
Incomplete heart block
in this condition, the transmission from the atria to the ventricle slows down but does not completely get blocked. It comes in four types: first degree heart block, second degree heart block, wenckebach phenomenon, bundle branch phenomenon
First degree heart block
It is called the delayed conduction. The conduction impulses through the AV node is very slow ie the AV nodal delay is longer. In ECG, the PR interval is very much prolonged and is more than 0.2 seconds.
Second degree heart block
it is called the partial heart block. In this case come of the impulses produced by SA node fail to reach the ventricles. So, one ventricular contraction occurs for every 2, 3 or 4 atrial contractions. In ECG the QRST complex (ventricular complex) is missing intermittently.
Wenckebach phenomenon or syndrome
It is a type of heart block characterized by progressive increase AV nodal delay resulting in missing of one beat. Afterwards the conduction of impulse is normal or slightly delayed. In ECG, the progressive lengthening of PR interval is noticed till a QRST complex disappears
Bundle branch block
when right or left branch of His is affected the right or left bundle block occurs. During this type of block, the impulse from atria reaches unaffected ventricle first. Then, from here the impulse travels to the affected side. So, ECG shows normal ventricular rate, but the QRS complex is deformed or prolonged.
Complete heart block (third degree heart block)
The impulses produced by the SA node do not reach the ventricles so the ventricles beat by their own rhythm. It is called idioventricular rhythm. Complete heart block occurs due to any of the following causes: Disease of AV node, which leads to AV nodal block and Defective conductive system below the level of AV node causing infranodal block.
AV nodal block
in this type of block a part of AV node is defective and the affected part becomes the pacemaker. The rhythm of AV node is about 45-60 per minute.
in this condition, the distal part of the conductive system becomes the pacemaker. The rhythmicity of Purkinje fibers is about 35 per minute. Sometimes the ventricular musculature itself becomes the pace maker and in those conditions and it beats at about 20 per minute. During complete heart block, a condition called Stokes Adams syndrome.
Stokes Adams syndrome
in many patients affected by heart block, the complete heart block occurs intermittently. When the block occurs, the ventricles stop beating immediately. The ectopic pacemaker (AV node, purkinje fiber or ventricular muscle) starts functioning only after 5 - 30 seconds. During this time, the blood circulation is affected because of lack of ventricular output. The brain cannot withstand the stoppage of blood supply and oxygen supply even for 5 to 6 seconds. Before the onset of discharge from ectopic pacemaker, dizziness and fainting occurs. If the discharge of impulse from ectopic pacemaker is delayed beyond 30 seconds, death occurs.
sometimes a part of the heart other than the SA node produces an impulse called an ectopic focus. This causes and extra beat. After this beat the heart stops in the relaxed state for a little time. This time is called the compensatory pause.
Cause for the compensatory pause
In the cardiac muscle the refractory period of the heart lasts till the end of the contraction . Since the impulse from the extopic focus causes an extrasystole, the heart has to wait till the next natural impulse from the SA node. This is the cause for the compensatory pause. The parts where the ectopic focus can originate are the AV node, the bundle of His, atrial musculature and ventricular musculature.
in atrial extrasystole, the extra P wave appears immediately after the regular T wave. The PR interval of this beat is short.
in the nodal extrasystole, the P wave is merged with QRS complex and all the chambers of the heart contract together.
The QRS complex follows the regular T wave. This QRS complex is a prolonged as the impulse conducted through the ventricular muscles and not through conductive system.
Conditions where extrasystole occurs
organic diseases of the heart. Emotions, severe exhaustion, excessive ingestion of coffee or alcohol, excessive smoking, hyperthyroidism, reflexes elicited from abnormal viscera.
It is the sudden increase in heart rate due to ectopi foci from atria, AV node or ventricle. It occurs suddenly and lasts for a few seconds to a few hours but it also stops suddenly and then the heart returns to normal. This tachycardia is of three types: Atrial Paroxysmal Tachycardia, Ventricular Paroxysmal Tachycardia and AV nodal Paroxysmal Tachycardia
Artial Paroxysmal Tachycardia
In this case, the ectopic impulses are discharged from any part of atrial musculature and conducted through the conductive system. HR is 150 - 220. The P wave is inverted and the rest of the ECG is normal.
Ventricular Paroxysmal Tachycardia
sometimes a part of ventricular muscle, particularly an ischaemic area is excited abnormally followed by a series of extrasystole. It is called ventricular Paroxysmal Tachycardia. This condition is dangerous as the circus movement is developed within ventricular muscle. This circus movement leads to ventricular fibrillation, which is fatal
AV nodal Paroxysmal Tachycardia
This type os arrythmia is due to an extra unusual conduction system that is formed between the artia and the ventricles. It is very common and seen in healthy persons. This system is formed by abnormal junctional tissues constituting a structure called bundle of Kent.
There is sudden and temporary block in the conduction system and as a result the impulses reach the ventricles from the SA node through the bundle of Kent. As the impulse reaches the ventricles, the regular bundle reopens and the impulse travels from the ventricles to the AV node IN REVERSE. This depolarlizes the atria resulting in an atrial contraction. This is called an atrial echo beat. The impulse then reenters the regula pathway and completes the circus movement. The circus movement repeats producing tachycardia. ECG shows normal QRST but an absence of P waves.
Wolff Parkinson White syndrome
When the person with bundle of Kent suffers from repeated atacks of AV nodal paroxysmal tachycardia, the condition is called Wolff Parkinson Syndrome.
Lawn Gangong Levin syndrome
In some persons, another type of abnormal conductive fibers is present. These fibers connect atria and distal part of conductive system bypassing the AV node. These persons are also prone to AV nodal paroxysmal tachycardia. This condition is knowns as Lawn Ganong Levin syndrome. The ECG shows short PR interval with normal QRS complex and T wave.
It is an atrial arrythmia associated with atrial paroxysmal tachycardia. The atria beat at about 250-350 beats per minute. The maximum rate of conduction of the AV node is about 240 per minute. So, during atrial flutter second degree heart block occurs.
Atria show irregular and rapid beats. 300-400 per minute. It is cause by circus movemtn within the artia musculature.
In this the vetricles beat irregularly and rapidly. They reach rates of 500 per minute. This is due to circus movement and is triggered by ventricular extrasystole. It may lead to death. It is common during an electric shock, coronary occulusion, chloroform anerthesia, cyclopropane anesthesia.
AV node as pacemaker
AV nodal rhythm
AV nodal extrasystole
AV nodal paroxysmal tachycardia
Artial musculature as pacemaker
atrial paroxysmal tachycardia
wolff parkinson white syndrome
lawn ganong levin syndrome
Ventricular musculature as pacemaker
ventricular paroxysmal tachycardia