An indiviual suffers bursts of tachycardia( an abnormally rapid and pronounced i

Question

An indiviual suffers bursts of tachycardia( an abnormally rapid and pronounced increase in heart rate). This individual's heart rate (HR) will rise from 70BPM up to 180-200BPM in seconds, lasting for about a minute, before falling back to resting HR. During tachycardia episode, this indiviual will start to fell somewhat dizzy, more near the end of the episode and for a few mintues after it is over. Explain the reason, focusing on cardiac output and with regard to cardiac function, this person feels dizzy after their tachycardia episodes.

Explanation / Answer

ANSWER:

TACHYCARDIA:Increase in heart rate(number of beats) per minute than the normal is called as Tachycardia.

Tachycardia leads to a fall in cardiac output.Diastole is too brief to allow proper filling of the heart so that each beat discharges only a small amount of blood.The rest period is very short , the heart fatigues and the signs of heart failure appears.

This leads to dizziness due to decreased oxygenated blood to the brain.

PAROXYSMAL TACHYCARDIA:In this condition the heart may suddenly accelerate to 150 or 200 beats per minute.The cardiac output fell from 5.6 litres to 2.5 litres and the output per beat fell from 77ml to 15ml.Diastole is too brief to allow proper filling of the heart,so that each beat only discharges a small amount of blood.The rest period is very short.

ECTOPIC ATRIAL TACHYCARDIAS:(FLUTTER AND FIBRILLATION)

Response of atria to rapid stimulation:As the frequency of stimulation of atria is increased the following events takes place:

In atrial flutter if the length of the pathway is sufficient the excitation process returns to the atrial ectopic focus to find it has recovered from its refractory period and the impulse is re-propagated round the circle.If the speed of the conduction of the impulse round the circle is slowed , the same state to affairs occurs.If the refractory period of the atrial muscle is shortened , the returning impulse will be repropagated.Any of these features may be seen in diseased hearts.

Ischaemia may slow conduction and drugs may shorten the refractory period.Flutter occurs clinically at a rate of 200-350 beats per minute,in diseased hearts.

In Atrial Fibrillation the atria exhibit no coordinated contraction,inspection of the heart shows merely an irregular tremulousness of the surface.Most of the atrial muscle fibres are completely or partially refractory at any instant and the excitation wave takes an irregular sinuos path.The AV node is stimulated at irregular intervals and the ventricular beats become irregular.Fibrillation commonly supervenes on flutter in diseased hearts and the atria may be excited as fast as 450 beats per minute.

ECG CHANGES:In paroxysmal atrial tachycardia the P wave is abnormal, usually inverted.and bears a constant relation to QRS complex.

In paroxysmal atrial flutter,the atrial flutter is so rapid that the atrial repolarization is affected.As a result each P wave is tend to be followed by an atrial T wave pointing in the opposite direction giving an undulated saw tooth appearance.

In atrial fibrillation there is no coordinated atrial contraction and therefore no P wave.

ETIOLOGY:

1.Mitral stenosis

2.Severe Hyperthyroidism

3.Coronary arterial disease

ECTOPIC VENTRICULAR TACHYCARDIA:Ventricular fibrillation is fatal unless treated promptly.It is the cause of sudden death in coronary occlusion.

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