Effect of lidocaine on the atrial fibrillation threshold

Lidocaine as an anti-arrhythmic drug: Are there any indications left?

Lidocaine is classified as a class Ib anti-arrhythmic that blocks voltage- and pH-dependent sodium channels. It exhibits well investigated anti-arrhythmic effects and has been the anti-arrhythmic of choice for the treatment of ventricular arrhythmias for several decades. Lidocaine binds primarily to inactivated sodium channels, decreases the action potential duration, and increases the refractory period. It increases the ventricular fibrillatory threshold and can interrupt life-threatening tachycardias caused by re-entrant mechanisms, especially in ischemic tissue. Its use was pushed into the background in the era of amiodarone and modern electric device therapy. Recently, lidocaine has come back into focus for the treatment of acute sustained ventricular tachyarrhythmias. In this brief overview, we review the clinical pharmacology including possible side effects, the historical course, possible indications, and current Guideline recommendations for the use of lidocaine.

Mechanisms of atrial fibrillation termination by rapidly unbinding Na+ channel blockers: insights from mathematical models and experimental correlates

Atrial fibrillation (AF) is the most common sustained clinical arrhythmia and is a problem of growing proportions. Recent studies have increased interest in fast-unbinding Na(+) channel blockers like vernakalant (RSD1235) and ranolazine for AF therapy, but the mechanism of efficacy is poorly understood. To study how fast-unbinding I(Na) blockers affect AF, we developed realistic mathematical models of state-dependent Na(+) channel block, using a lidocaine model as a prototype, and studied the effects on simulated cholinergic AF in two- and three-dimensional atrial substrates. We then compared the results with in vivo effects of lidocaine on vagotonic AF in dogs. Lidocaine action was modeled with the Hondeghem-Katzung modulated-receptor theory and maximum affinity for activated Na(+) channels. Lidocaine produced frequency-dependent Na(+) channel blocking and conduction slowing effects and terminated AF in both two- and three-dimensional models with concentration-dependent efficacy (maximum approximately 89% at 60 microM). AF termination was not related to increases in wavelength, which tended to decrease with the drug, but rather to decreased source Na(+) current in the face of large ACh-sensitive K(+) current-related sinks, leading to the destabilization of primary generator rotors and a great reduction in wavebreak, which caused primary rotor annihilations in the absence of secondary rotors to resume generator activity. Lidocaine also reduced the variability and maximum values of the dominant frequency distribution during AF. Qualitatively similar results were obtained in vivo for lidocaine effects on vagal AF in dogs, with an efficacy of 86% at 2 mg/kg iv, as well as with simulations using the guarded-receptor model of lidocaine action. These results provide new insights into the mechanisms by which rapidly unbinding class I antiarrhythmic agents, a class including several novel compounds of considerable promise, terminate AF.

Blood cardioplegia delivery. Deleterious effects of potassium versus lidocaine

Delivery of cardioplegic (CP) solutions to all regions of the myocardium is critical for optimal myocardial protection during cardiac surgery. However, there are little data regarding the effects of CP agents upon coronary vascular resistance (CVR) and CP delivery. Accordingly, we evaluated blood CP (Hct 30) delivery and CVR during 75 minutes of multi-dose hypothermic blood CP arrest in an in vivo isolated dog heart preparation. Three groups of dogs were studied: K(K+ = 30 mEq/L; n = 6), L (Lidocaine = 400 mg/L; K+ = 4 mEq/L; n = 6), and KL (K+ = 30 mEq/L, Lidocaine 400 mg/L; n = 6) during total cardiopulmonary bypass and moderate systemic hypothermia (28 C). Basal CVR was calculated by measuring total coronary flow (HR 120/min; mean aortic pressure = 80 mmHg) in the empty beating heart. After aortic cross-clamping, the blood CP solution was infused into the aortic root at a constant pressure (80 mmHg) and constant temperature (16 +/- 2 C) for 60 seconds at 15 minute intervals for a total arrest time of 75 min. Total CP flow, CVR, O2 consumption, lactate extraction/production, and K+ balance during 75 minutes of arrest and 30 minutes of reperfusion were determined. The distribution of the CP solution in the left ventricle was measured with radioactive microspheres (9 +/- 1 mu). Biopsy specimens were taken to measure wet to dry ratios. Values are mean +/- SEM. Data were analyzed by BMDP-P2V. During the first CP infusion, after aortic cross-clamping, no differences in CVR or CP distribution were found among the three groups. However, CVR was increased significantly in the K group during the second CP infusion (O': 0.98 +/- 0.20 mmHg/ml/min/100 g; 15': 2.66 +/- 0.82; p less than 0.001). The CVR remained high for the remainder of the arrest period. Moreover, total, epi- and endocardial flow decreased significantly (54%, p less than 0.001). In groups L and KL, no significant changes in CVR were seen. Groups K and KL showed a significant K+ extraction during the first CP infusion. During the early reperfusion period, K+ washout occurred in these two groups, which was not seen in the L group. There was no significant difference between the three groups in myocardial O2 consumption, lactate metabolism, and water content during the arrest and the reperfusion period. In conclusion, high concentrations of K+ (30 mEq/L) can markedly increase CVR and impair blood CP delivery and distribution. These effects can be prevented by lidocaine. These findings warrant reassessment of the various additives to CP solutions and their effects on CVR and CP distribution during multi-dose hypothermic CP arrest.

Electrical behavior of the heart following high-potassium cardioplegia

The electrical activity of the heart was studied in 25 patients undergoing elective coronary artery bypass grafting. Simultaneous surface electrocardiograms and bipolar atrial electrograms were monitored continuously from the onset of cardioplegic arrest until normal sinus rhythm was reestablished. Several observations were made. (1) Administration of cardioplegia promptly induced and maintained ventricular arrest in all patients. (2) Atrial activity was seen in 23 patients during global ischemia. (3) Following unclamping, the first sustained rhythm was atrial in 22 patients and was associated initially with high-grade atrioventricular block progressing to 1:1 conduction after a mean reperfusion time of 23 minutes. (4) The time required for complete electrical recovery varied directly with the cross-clamp time and the amount of cardioplegic solution used. (5) Only 3 patients required ventricular defibrillation. (6) In the postoperative period, supraventricular tachyarrhythmias developed in 6 patients. Their occurrence appeared to be related to prolonged atrial activity during the cross-clamp period. Although cardioplegia administration maintained ventricular arrest, sustained atrial activity often was present, perhaps implying inadequate atrial protection and predisposing to atrial arrhythmias. Normal sinus rhythm was reestablished spontaneously in all patients. The atrial electrogram proved essential in the precise intraoperative recognition of cardiac rhythm.

Effects of lignocaine on bidirectional tachycardia and on digitalis-induced atrial tachycardia with block

Most recent studies discussing tachycardias with alternating QRS polarity have referred to those known as torsade de pointes. This report, in contrast, deals with bidirectional tachycardia and the effects of lignocaine on 10 patients with this arrhythmia. Three of the patients also had digitalis-induced atrial tachycardia with block. In one patient, a single bolus of lignocaine was followed (five minutes later) by ventricular fibrillation, but the other nine patients received two boluses of 75 mg followed by a drip infusion of 3 mg/min. The drug terminated the episodes of atrial tachycardia with block and bidirectional tachycardia in all patients thus treated. Whereas the abolition of the bidirectional tachycardia was permanent in the seven patients with digitalis intoxication, it recurred after stopping the drip infusion in the two patients without digitalis toxicity. It is concluded that lignocaine can be useful in the treatment of digitalis-induced bidirectional tachycardia and atrial tachycardia with block. From this study no conclusions can be drawn, however, as to whether lignocaine is superior to other class I or class IV agents.

The effects of lidocaine on the ventricular fibrillation threshold and primary ventricular fibrillation following acute experimental coronary occlusion

Experiments were performed on 39 anaesthetized open-chest dogs (BW 16-33 kg) to examine the effect of lidocaine on the frequency of primary ventricular fibrillation (VF) and the time course of the ventricular fibrillation threshold (VFT) (train of stimuli-method) following acute coronary artery occlusion, and also to study the effects of lidocaine on the VFT of non-ischaemic heart at different therapeutic and high non-therapeutic doses. At effective plasma levels of lidocaine usually reached in clinical therapy (130-480 micrograms/l) there was no measurable increase in VFT compared to control values. The drop in VFT following acute ligation of the left anterior descending coronary artery (LAD) was neither eliminated nor even merely diminished. After occlusion of the left circumflex coronary artery (CIR), the incidence of spontaneous VF was not reduced in comparison to a control group. With regard to the doses administered and the plasma levels of lidocaine achieved, only the application of clinically extremely high or toxic doses resulted in increases in VFT in the non-ischaemic heart.