SINUS ARRHYTHMIA….It is a type of arrhythmia characterized by increased heart rate during inspiration and slowing of heart rate during expiration.
- Normally the cardiac centre is inhibited by respiratory centre. At the height of inspiration it itself is depressed, so its depressing effect over cardiac centre is minimised and thus heart rate is increased.
- During inspiration right atrium is filled up with blood stretch auricular reflexes will stimulate the cardiac centre and thus heart rate is increased. As in ASD the atrium is already overfilled with blood, deep inspiration cannot stretch it any more sinus arrhythmia does not occur There are two types: (1) Respiratory form mainly seen in extremes of age and athletes and (2) non-respiratory form which is not related to respiration but is due to vagal stimulation of the G.I. tract and at times in digitalis toxicity. Variable pulse frequency remains within 10%.
Ventricular premature beats are the forerunners of ventricular tachycardia or fibrillaltion. So prophylactic Lidocaine is given I mg/kg IV by bolus followed by infusion in the dose of 2 mg per minute. If ventricular premature beats (VPB) occur more than 6/min, there is R on T phenomenon, multifocal ectopics and short runs of ventricular tachycardia, additional bolus of Lidocaine 0.5 mg/kg is to be given followed by infusion at an increased rate of 4 mg/min. One should be cautious about the toxicity like, anxiety, confusion, tremor or convulsion which occurs particularly in older individuals or in association with liver disease, heart failure or hypotension. After 3-4 hours,infusion rate should be reduced and the drug is to be continued for 24 hours.
I mg/kg bolus of Lidocaine is to be started when patient is stable. In unstable patients electrical cardioversion is to be started with 100 J. If Lidocaine fails, Procainamide should be started with 100 mg bolus in 1-2 minutes time, repeated every 5 minutes upto a dose of 750 to 1000 mg. This is followed by an infusion in a dose of 20-80 ug/kg/min. Complications like hypotension, conduction disturbances or depression of myocardial function may develop. If there is no response, B-blocker like Esmolol 500 Hug per kg IV to be followed by 50-200 Hg/kg/min; Phenytoin with a starting bolus dose of 100 mg for 5 minutes to be repeated after 5-10 minutes till a total dose of 1000 mg is reached when maintenance dose of 400- 500 mg/day; Bretylium tosylate 5 mg per kg IV for 3-5 minutes repeated every 20 minutes followed by 0.2 mg infusion/min; Amiodarone IV in a dose of 5-10 mg/kg can also be given.