Tachycardia and Bradycardia causes and symptoms

PAROXYSMAL TACHYCARDIA

Paroxysmal tachycardia is the sudden attack of increased heart rate due to ectopic foci arising from atria, AV node or ventricle. It is also called Bouveret- Hoffmann syndrome.

Increase in heart rate due to ectopic foci arising from either atria or AV node is called supraventricular tachycardia (SVT). It differs from ventricular tachycardia, which does not depend upon atria or AV node. The attack lasts for a period of few seconds to few hours. It also stops suddenly. After the attack, heart functions normally. Symptoms include palpitations, chest pain, rapid breathing and dizziness.

Paroxysmal tachycardia is of three types:

1. Atrial paroxysmal tachycardia

2. AV nodal paroxysmal tachycardia

3. Ventricular paroxysmal tachycardia.

1. Atrial Paroxysmal Tachycardia

Atrial paroxysmal tachycardia is the sudden increase in heart rate caused by ectopic impulses discharged from atrial musculature. Heart rate is 150 to 220/minute. P wave in ECG is inverted, with normal QRST.

2. AV Nodal Paroxysmal Tachycardia – Bundle of Kent

AV nodal paroxysmal tachycardia is the sudden increase in heart rate caused by ectopic foci arising from AV node due to a temporary block in the conductive system. It also involves circus movement. This type of tachycardia is very common in some healthy persons who have got an additional conductive system. This system is formed by some abnormal junctional tissues constituting a structure called bundle of Kent. Bundle of Kent connects the atria and ventricles directly, so the conduction is very rapid than through the regular conductive system.

Circus movement – Re-entry and atrial echo beat

Circus movement is defined as circuitous propagation of impulses around a structural or functional obstruction, resulting in re-entry of the impulse and re-excitation of heart. When there is a sudden and temporary block in normal conductive system, the impulses from SA node reach the ventricle through bundle of Kent. By this time, the blockage in normal conductive system disappears. Now, the impulse, which passes through bundle of Kent, after exciting the ventricular muscle, travels in the opposite direction through the normal conductive system and finally, it re-enters the AV node. Re-entered impulse activates the AV node and depolarizes the atria, resulting in atrial contraction. It is called atrial echo beat.

Re-entered nodal impulse simultaneously spreads to ventricle through normal conductive system,

completing the circus movement. This circus movement is repeated producing tachycardia called AV nodal paroxysmal tachycardia. ECG shows normal QRST complex. But P wave is mostly absent.

Wolff-Parkinson-White syndrome

Wolff-Parkinson-White syndrome is the condition characterized by repeated attacks of AV nodal

paroxysmal tachycardia in persons with bundle of Kent. ECG shows short P-R interval with normal QRS complex and T wave.

Lown-Ganong-Levin syndrome

Lown-Ganong-Levin syndrome is another condition characterized by AV nodal paroxysmal tachycardia.

This occurs in persons who have got another type of abnormal conductive fibers like bundle of Kent. These fibers also connect atria and distal part of conductive system directly bypassing the AV node. So the impulse from SA node reaches ventricle through the abnormal conductive fibers. After exciting the ventricular muscle, the impulse travels in opposite direction through normal conductive system and finally, it re-enters the AV node. The re-entered impulse activates the AV node causing atrial contraction. ECG shows short P-R interval with normal QRS complex and T wave.

3. Ventricular Paroxysmal Tachycardia

Ventricular paroxysmal tachycardia is the sudden increase in heart rate caused by ectopic foci arising

from ventricular musculature. Sometimes, a part of ventricular muscle, particularly an ischemic area is

excited abnormally, followed by a series of extrasystole. This condition is dangerous as the circus movement is developed within ventricular muscle. This circus movement leads to ventricular fibrillation, which is fatal.

ATRIAL FLUTTER

Atrial flutter is an arrhythmia characterized by rapid ineffective atrial contractions, caused by ectopic foci

originating from atrial musculature. It is often associated with atrial paroxysmal tachycardia. Both the atria beat rapidly like the wings of a bird, hence the name atrial flutter. Atrial rate is about 250 to 350/minute. Maximum number of impulses conducted by AV node is about 230 to 240 /minute. So, during atrial flutter, the second degree of heart block occurs. The ratio between atrial beats and ventricular beats is 2 : 1 or sometimes 3 : 1. Atrial flutter is common in patients suffering from cardiovascular diseases such as hypertension and coronary artery disease. Initially, it is marked by palpitations that are unnoticed. However, prolonged atrial flutter may lead to atrial fibrillation or heart failure.