Frequent Ventricular Premature Contractions under Anaesthesia in Prone Position.

Sir,

A 36-yr-old male of ASA physical status 1, presented with low backache, weakness and loss of sensation in both the lower limbs for 2 years. The patient was diagnosed to have lumbar canal stenosis (L2- L5) Hence, foraminotomy and decompression at the level of L3,4 and L4,5 was planned. There was no history of any respiratory or cardiovascular abnormalities. All routine investigations including ECG were within normal limits. In the operation theater, the routine monitors were connected, and an intravenous (IV) access was secured. Anaesthesia was induced with propofol 1mg/ kg and fentanyl 2μg/kg. Tracheal intubation was facilitated with rocuronium 1mg/kg. Maintenance of anaesthesia was done with isoflurane, N2O and oxygen (2:1) along with intermittent boluses of rocuronium and fentanyl. The haemodynamic parameters were normal till this time. However, frequent ventricular premature contractions (VPCs) were observed after the patient was made prone [Figure 1]. The VPCs subsided spontaneously, only to recur after few minutes. An arterial blood gas (ABG) analysis was done which did not reveal any abnormality. Initially, VPCs were less frequent (<5 beats/min), hence, no additional treatment was given. Subsequently, there were frequent VPCs (>10 beats/min) which subsided with administration of lignocaine 1.5 mg/kg IV. A 12-lead ECG was obtained, and cardiologist's opinion was sought. The patient was observed for next 30 minutes. Frequent VPCs recurred; hence, lignocaine infusion at the rate of 2 mg/min was started. As there was no haemodynamic instability, it was decided to continue with the surgery. The total duration of surgery was 4 hours, during which 3 episodes frequent VPCs (>5 beats/min) were observed. Rest of the surgery was uneventful, at the end of which the trachea was extubated after reversal of residual neuromuscular blockade. The patient was transferred to intensive care unit (ICU) for observation. The postoperative ECG and echocardiography were normal and the patient was discharged on 3rd postoperative day.

Figure 1

ECG recording showing normal rhythm just before positioning (top); with VPCs (arrow) after prone position (bottom)

VPCs result from ectopic foci arising from abnormal site in the ventricular myocardium below atrioventricular node (AV) and give rise to wide bizarre QRS complex. Conditions like coronary artery insufficiency, myocardial infarction, digitalis toxicity with hypokalemia and hypoxaemia give rise to VPCs.1 New-onset VPC should be considered life-threatening as it may progress to serious ventricular arrhythmias like tachycardia and ventricular fibrillation.2 VPCs are more likely to lead to ventricular fibrillation if they are multiple, multifocal or bigeminal; occur near the vulnerable period of the preceding ventricular repolarization (R-on-T phenomenon); or appear in short-long-short coupling sequences.23 The first step management of VPCs is to treat the underlying abnormalities. Isolated VPCs in asymptomatic and healthy patients do not require treatment. However, VPCs which are multiple (>5 beats/min), with haemodynamic disturbance or harbinger of worse arrhythmias require prompt treatment. Lignocaine with an initial bolus dose of 1.5 mg/kg followed by infusion of 1-4 mg/min is the treatment of choice. Esmolol, propranolol, procainamide, quinidine, disopyramide, atropine, verapamil, and overdrive pacing are other therapeutic modalities.12

In this case, unexplained multiple VPCs were encountered in an otherwise normal patient after prone position under anaesthesia. However, our literature search revealed nothing on occurrence of VPCs in relation to prone position. Therefore, we attribute anaesthetic agents as the cause of VPCs. Volatile anaesthetics has potential to cause bradycardia, AV conduction abnormality and prolongation of QTc interval. Reversible AV dissociation has been reported in humans anaesthetised with N2O and volatile anaesthetics.4 As frequent VPCs can cause serious ventricular arrhythmias, it is difficult on the part of anaesthesiologists to decide whether to continue with the surgery in this scenario or not. Nevertheless, the above experience reaffirms continuation of surgery in a haemodynamically stable patient on lignocaine infusion with preparation to deal with possible serious arrhythmias.