Paroxysmal Tachycardias And Wolff-Parkinson-White Syndrome As Unique Forms Of Arrhythmias
Ectopic foci Of Impulse Conduction
These are tachycardias produced as a result of ectopic foci of impulse production (in contrast to sinus tachycardia in which the normal pacemaker produces impulses) or as a result of re-entry phenomenon. All the paroxysmal tachycardias are characterized by abrupt onset. Paroxysmal tachycardias may be divided into:
- Supraventricular: atrial and junctional A-V junction
- Ventricular: depending on the focus of impulse production.
Symptoms of all the tachycardias are similar, i.e palpitation, angina pain or syncope. In all the arrhythmias, ECG is absolutely essential to arrive at the diagnosis.
A Heart Rhythm DIsorder
Paroxysmal atrial tachycardia (PAT)
Impulses arise in the atrium and the arrhythmia is usually produced as a result of re-entry phenomenon. The heart rate varies from 140-230/min and the rhythm is regular. The ECG shows normal QRS with a rate of 140-230/min. In some cases, the P-waves may be identifiable preceding the QRS. Vagal stimulation (Carotid pressure, swallowing ice-cold water or pressure over eyeball) generally counters the attack.
Common causes are excess of caffeine or tobacco, alcohol, anxiety or thyrotoxicosis. In the majority, there is no underlying cardiac disease.
SA And AV Nodes
Paroxysmal atrial tachycardia with block (PATB)
This is a special form of PAT in which some of the atrial impulses are not conducted down to the ventricles. This gives rise to varying grades of atrioventricular block. This abnormality is characteristically seen in digitalis toxicity.
Treatment: The treatment consists of the following:
- Carotid sinus massage in the recumbent posture may serve to abolish PAT. Only one side should be massaged at a time.
- Intravenous administration of verapamil 10-20 mg gives prompt relief.
In resistant cases, DC shock may be required. The treatment of PATB is that of digitalis toxicity.
A-V Junctional Tachycardia
Both paroxysmal (Ventricular rate 130-240/min) and non-paroxysmal (ventricular rate 70-140 min) forms exist. The ECG shows normal QRS complexes, but the P-wave follows the QRS.
An Uncommon Kind Of Tachycardia
Wolff-Parkinson-White Syndrome (Pre-excitation Syndrome)
This abnormality is found not uncommonly. In this condition, the P-R interval is considerably shortened because of the presence of accessory pathways for A-V conduction. These pathways conduct impulses at much faster rates than the normal A-V node. Due to the same reason, circus movement of impulses may occur at the a-v junction and give rise to paroxysmal supraventricular tachycardias.
Such individuals also run the risk of developing ventricular tachycardia and ventricular fibrillation. The ECG is diagnostic. His-bundle electrography gives better details of the abnormality.
Treatment: Drugs such as digoxin, beta-adrenergic blockers or verapamil reduce the conduction along the normal pathways. Drugs such as quinidine, procainamide and disopyramide reduce conduction through the abnormal pathways as well. When medical therapy fails electrical stimulation to produce a suitably timed extrasystole may serve to terminate the attack. In intractable cases, surgical interruption of the abnormal bundle gives permanent relief.
© 2014 Funom Theophilus Makama