This is called ectopic beat because of its origin other than SA-node that is in the ectopic site. As the beat may occur premature to scheduled SA-beat it is also called premature beat. It is also called extra systoles as sometimes the premature impulse may produce additional beat resulting in heart sounds and pulse therefrom.
These are ectopic impulses which arise from sites other than SA node and give rise to ventricular response whenever they reach the ventricle outside its refractory period. Mechanism is controversial, however it is believed that
Atrial, AV junction and ventricular depending on the site of topic impulse formation. Ventricular type is commonest.
Symptoms may or may not be present. If present these are due to three reasons:
Small beat following a short pause; big beat following a long pause are felt at the wrist except in cardiomyopathy. Sometimes no beat may be felt corresponding to an auscultatory sound when the extrasystole is too premature. In cases of auricular ectopics jugular pulse may show all the waves and auscultation may not reveal any change in the heart sound, In junctional ectopics when the focus is located in AN region there may be accentuated S1. In mid nodal or NH zonal ectopics a prominent jugular cannon pulsation may be seen. In cases of ventricular ectopics when the focus is located in the left ventricle wide splitting of S1 and S2 may be audible. When the ventricular focus is located over theright ventricle reversed splitting of S2 may develop. In ventricular ectopics compensatory pause is more. After the pause one must auscultate carefully the post pause beat. In Aortic stenosis the murmur becomes accentuated due to forceful contraction of the left ventricle. But the murmur of mitral regurgitation or cardiomyopathy will not accentuated. The extrasystole may occur after one or two normal beats regularly in couples or triples giving rise to pulsus bigeminus or trigeminus. Pulsus bigeminus is commonly seen as a sign of digitalis overdose. Atrial ectopics are not of much significance but frequent atrial ectopics in a patient of mitral stenosis may herald the onset of auricular fibrillation; similarly frequent occurrence of ventricular ectopics particularly presence of R on T phenomenon is an ominous sign in acute myocardial infarction as it may lead to ventricular tachyarrhythmias. Pulse deficit may be present and it is usually within 10 beats per minute.
ECG will help in the diagnosis. In atrial ectopic P waves become bizarre, while in ventricular ectopics QRS duration is wide with T wave directed opposite to the main QRS complex. In junctional rhythm when focus is in the AN region P wave is inverted, PR interval becomes short. When focus is in the NH region P appears after QRS complex and is inverted. In mid-junctional rhythm P wave is overlapped by QRS complex, hence cannot be identified.
Pulse rate is usually more than 100/min, it is extremely irregular, effect of pause on the subsequent pulse is completely erratic and after exercise irregularity increases. Pulse deficit is more than 20 beats/minute. If mitral stenosis is present then presystolic accentuation may disappear. ECG will help in diagnosis.
Partial heart block
During the period of intermission of pulse no heart sounds are heard but Jugular venous a wave is present. Pulse deficit is absent. ECG is diagnostic
. In gross electrolyte imbalance or in digitalis inducedcases Potassium chloride 1-3 gm four times a day may be given.
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