Effects of lidocaine on regional intraventricular conduction in patients with coronary artery disease

Preferential action of mexiletine on central common pathway of reentrant ventricular tachycardia

OBJECTIVES

The action of mexiletine on diseased myocardium was assessed in reentrant ventricular tachycardia (VT).

BACKGROUND

Whether class Ib antiarrhythmic agents exert a preferential action on the central common pathway of reentrant ventricular tachycardia has not yet been studied in humans.

METHODS

In 10 consecutive patients (7 with a previous myocardial infarction, 3 with nonischemic disease), VT was induced and entrained with rapid pacing. The orthodromic conduction time was measured from stimulus to the entrained electrogram at the exit from the presumed central common pathway (i.e., the earliest site of activation). Mexiletine at 125 to 250 mg was administered intravenously, and when VT with the same configuration was induced, the study was repeated. The action of mexiletine on the central common pathway was assessed from the changes in VT cycle length and orthodromic conduction time. The effects on QRS complex duration, local conduction time between the exit and the pacing site and duration of the local electrogram were compared between normal and diseased myocardium.

RESULTS

Mexiletine prolonged the VT cycle length in all patients, from (mean +/- SD) 316 +/- 30 to 360 +/- 64 ms (mean change 20 +/- 7%, p < 0.001); during entrainment of VT, the orthodromic conduction time was prolonged, from 306 +/- 58 to 367 +/- 89 ms (mean change 18 +/- 9%, p < 0.001). These changes were highly correlated (r = 0.95, p < 0.001). QRS duration changed little (4 +/- 3%), and local conduction time showed no change. The duration of the fragmented electrogram width was prolonged by mexiletine: from 146 +/- 50 to 176 +/- 56 ms (mean change 23 +/- 8% during VT, p < 0.001). Only a slight change occurred in the effective refractory period, both at the pacing site and at the exit.

CONCLUSIONS

Mexiletine caused little change in conduction time in normal myocardium but prolonged VT cycle length, orthodromic conduction time and duration of the local electrogram at the earliest site of activation of VT. From these findings, a preferential action of mexiletine on diseased myocardium was suggested but seemed to occur only at higher frequencies during tachycardia.

Facilitation of reentry by lidocaine in canine myocardial infarction

The authors studied the effects of lidocaine in 18 consecutive dogs with myocardial infarction 1 to 4 days after two-stage left anterior descending coronary artery ligation. Electrophysiologic testing was performed in anesthetized dogs after infarction with single-, double-, or triple-programmed extrastimuli or rapid bursts (3 beats at 240 to 420 beats/min) delivered to the right ventricular outflow tract. Inducibility of sustained monomorphic ventricular tachycardia after an intravenous bolus of lidocaine (3 to 6 mg/kg) was compared in the same animal to the premedicated state. In the control state, sustained monomorphic ventricular tachycardia was inducible in 6 of 18 dogs. After administration of lidocaine, electrically induced sustained monomorphic ventricular tachycardia was initiated in an additional nine dogs (which were previously noninducible; after lidocaine administration vs control p < 0.02). The antiarrhythmic agent induced further rate-dependent slowing of conduction in the periinfarction subepicardium, which at a critical value of rate and amount of conduction delay resulted in sustained reentrant monomorphic tachycardia. These results show that lidocaine has marked proarrhythmic action in this canine model of myocardial infarction, probably because of its depressant effect on injured cardiac tissue.

An undocumented effect of lidocaine revealed by computerized electrocardiography

The influence of an intravenous push of lidocaine 1 mg/kg followed by 2 mg/min infusion on total QRS amplitude and R-to-S duration in leads V2-V4 of the electrocardiogram was studied in 11 patients who were hospitalized in the coronary care unit. A computerized system sampled the amplitude and timing of peak R and S waves of 1100 QRS complexes of leads V2-V4, starting two minutes before the first push of lidocaine. Curves of amplitude and R-to-S duration versus time were obtained in all patients. QRS amplitude in V2 and V3 increased significantly in 10 of 11 patients (p < 0.005). The mean voltage increase for all patients was 0.1 +/- 0.07 millivolt. The authors also observed a mild prolongation of R-to-S duration (0.8 +/- 1.0 millisecond p < 0.02). This new finding, obtained by a simple computerized system, may possibly have potential future practical clinical application as a feedback parameter for closed-loop control systems for the administration of lidocaine.

Effects of lidocaine and procainamide on normal and abnormal intraventricular electrograms during sinus rhythm

The effect of lidocaine (n = 6) and procainamide (n = 12) on electrogram characteristics from electrically normal right ventricular and electrically abnormal left ventricular endocardial sites was determined in 18 patients with prior myocardial infarction. Bipolar electrograms were recorded during sinus rhythm with No. 6F catheters positioned at a left ventricular abnormal site (electrograms fulfilling two of the following criteria: amplitude less than 3 mV, duration greater than 70 msec, or an amplitude to duration ratio less than .046) and normal sites at the right ventricular apex (RVA) and right ventricular outflow tract (RVOT). All electrograms were recorded from the same location before and after intravenous lidocaine or procainamide administered to obtain mean serum concentrations of 4.2 +/- 0.6 and 9.42 +/- 2 micrograms/ml respectively. Lidocaine and procainamide had no significant effect on sinus cycle length or electrogram amplitude. After lidocaine, no significant change in QRS width (112 +/- 23 vs 114 +/- 24 msec), left ventricular electrogram duration (76 +/- 21 vs 78 +/- 15 msec), or right ventricular electrogram duration (RVA 33 +/- 9 vs 33 +/- 10 msec, RVOT 31 +/- 9 vs 33 +/- 11 msec) was noted during sinus rhythm. At a paced cycle length of 600 msec, there was also no change in the paced QRS duration (197 vs 198 msec), the RVA electrogram duration (30 vs 32 msec), the RVOT electrogram duration (49 vs 52 msec), or the left ventricular electrogram duration (102 vs 108 msec).(ABSTRACT TRUNCATED AT 250 WORDS)

Prolongation of refractoriness and activation time in normal canine ventricular myocardium following bolus administration of lidocaine

This study examines the electrophysiologic effects of an intravenous bolus of lidocaine in the normal canine ventricle. In 14 open-chest dogs, left ventricular effective refractory period, ventricular repolarization time, and activation time were measured continuously during ventricular pacing (150/min) before, during, and after intravenous lidocaine given over 4 minutes. Lidocaine doses of 1.25, 2.5, and 5.0 mg/kg transiently prolonged the ventricular effective refractory period from 177 +/- 4 (X +/- standard error of the mean) to 185 +/- 5 msec (p less than 0.05), 176 +/- 3 to 188 +/- 6 msec (p less than 0.05), and 176 +/- 5 to 197 +/- 5 msec, (p less than 0.05), respectively, at 6 +/- 1.5 minutes from the onset of the bolus. Serum lidocaine levels obtained at the peak of the effective refractory period prolongation averaged 4.3 +/- 1.0, 9.0 +/- 3.0, and 22.3 +/- 4.7 micrograms/ml, respectively. Ventricular repolarization time was not prolonged. Activation time also transiently increased from 43 to 45 msec (p less than 0.05) and from 47 to 52 msec with the 2.5 mg/kg and 5.0 mg/kg doses, respectively. Cardiac denervation and administration of propranolol, 1 mg/kg intravenously, did not influence these responses to lidocaine. We conclude that a bolus of lidocaine transiently prolongs the effective refractory period and activation time in the normal canine ventricle because of its direct membrane rather than autonomic effects.

Rate dependent variation in concealed bigeminy

A 63 year old man with angina pectoris was found to have frequent extrasystoles separated by odd as well as even numbers of conducted sinus beats. Analysis of 935 conducted sinus beats showed that premature ventricular beats without interpolation were separated by odd numbers of conducted sinus beats in 117 sequences and even numbers (exceptions) in 48 sequences (p less than 2 X 10(-4)). Tabulation of cycle lengths revealed that cycles with even numbers of conducted sinus beats were characterized by a significant reduction in the preceding postextrasystolic pause (1441+/-76 msec vs. 1487 +/-59 msec; p less than .001) and second sinus cycle (720 +/- 44 msec vs. 750 +/- 38 msec; p less than .001). Premature ventricular beats were interpolated in 41 additional sequences. Interpolated extrasystoles were separated by the expected even numbers of conducted sinus beats in 39 cases and odd numbers (exceptions) in only two cases. The frequency of exceptions to the usual rules for concealed bigeminy was therefore 2/39 during interpolation and 48/117 without interpolation (p less than .01). This case demonstrates that: 1) a reduction in cycle length may be associated with exceptions to the usual rules for concealed bigeminy, and 2) the frequency of exceptions to concealed bigeminy may be altered by the presence of interpolation. Only one previous case has contained statistical documentation of these circumstances. The diagnosis of a concealed ventricular rhythm may be facilitated by careful analysis at multiple cycle lengths.