Mike Billie

Cardiac Arrhythmias Following Intravenous Nicotine: Experimental Study in Dogs

Background: Nicotine, the active agent in tobacco, is released into the circulation during cigarette smoking. It elevates plasma catecholamines, heart rate, and arterial blood pressure; produces coronary spasm; and increases myocardial work and oxygen demand with con comitant reduction in oxygen supply. This may generate cardiac arrhythmias that might con tribute to an increased incidence of sudden death due to smoking. It is hypothesized that acute administration of nicotine will induce cardiac arrhythmias, and this experimental study was planned with an aim to assess arrhythmogenic activity as a result of acute administration of nicotine. Methods: Nicotine was administered in different doses intravenously in 16 anesthesized dogs, and 52 experiments were carried out at weekly intervals. In each experiment, continu ous electrocardiograph rhythm strip records were obtained for 30 minutes before and follow ing anesthesia and after nicotine administration. They were scrutinized by two experienced electrocardiographers at intervals of 1, 2, 3, 4, 5, 10, 15, and 30 minutes. Results: Data revealed nonsignificant arrhythmias with doses of 2.5, 5.0, and 10.0 mg/kg of intravenous nicotine. The dose of 50 μg/kg induced supraventricular arrhythmias, atrioven tricular junctional arrhythmias, and ventricular arrhythmias. Supraventricular bradycardia in 30 (83%; P < .000 1), supraventricular arrhythmia in 30 (83%; P < .0001), sinus arrest in 18 (50%; P < .003). atrial ectopics in 24 (67%; P < .0004), and atrial tachycardia in 9 experi ments (25%; P < .021). These results were statistically significant. In 18 experiments, sinus arrest was observed to be missing P waves and QRS complexes for a period corresponding to 4:1-10:1 SA block, lasting 2-6 seconds, within 3 seconds of injection. Occurrence of wan dering pacemaker was observed in 6 experiments, atrial flutter in 2, and atrial fibrillation in 2, but these incidents were not significant. Atrioventricular junctional arrhythmias consisted of escape beats in 9 subjects (25%; P < .02), premature contractions in 12 (33%; P < .005), first-degree heart block in 9 (25%; P < .02), second degree heart block in 9 (25%; P < .02) and atrioventricular dissociation in 9 (25%; P < .02). All arrhythmias in this category were significant. Ventricular arrhythmias consisted of ventricular premature contractions that were unifocal in 32 subjects (89%; P < .0001), multifocal in 30 (83%; P < .0001), bigeminy in 28 (78%; P < .0003), trigeminy in 18 (50%; P < .003), interpolated in 15 (42%; P < .004), and salvos in 18 (50%; P < .003). Sustained ventricular tachycardias (> 30 beats) in 12 experi ments (33%; P < .005) proved significant. The dose of 100 μg/kg induced fatal ventricular flutter and ventricular fibrillation. The dog expired and experiments with that dose were not repeated. Conclusion: Data reveal dose-dependent arrhythmogenecity of nicotine in dogs. Smaller doses of nicotine did not produce significant arrhythmias. Higher doses, bioequivalent to smoking two standard cigarettes, may generate cardiac arrhythmias of simple to severe nature. Further work in human beings may confirm whether nicotine in cigarette smoke will generate similar cardiac arrhythmias especially in patients with autonomic imbalance and/or compromised and ischemic myocardium.

Combined effects of alcohol and nicotine on cardiovascular performance in a canine model.

Alcohol and tobacco consumption are correlated. Smokers consume more alcohol than do nonsmokers, and alcohol consumers smoke more than do teetotalers. The independent effects of alcohol and nicotine on the cardiovascular system are well documented, but combined effects of short-term administration are unknown. This experimental work was designed to study the effects due to short-term administration of alcohol and nicotine on cardiovascular system. In phase I, 30 experiments were performed to study the dose-response curve of both the drugs. In phases II and III, 15 dogs were subjected to 30 experiments. In phase II, ethanol, 400 mg/kg, was given i.v., followed by nicotine 50 microg/kg, i.v., and in phase III, sequence of drug administration was reversed to study the effects on hemodynamics and coronary artery blood flow. The dose-response curve established the i.v. dose of ethanol, 400 mg/kg, and nicotine, 50 microg/kg. Ethanol administration caused a nonsignificant increase in heart rate (HR), mean arterial pressure (MAP), left ventricular systolic pressure (LVS), and left ventricular mechanical work (LVMW), and a decrease in maximal rate of increase of LV pressure per second (dP/dt), stroke volume (SV), and systemic vascular resistance (SVR). Left ventricular end-diastolic pressure (LVEDP), pulmonary artery mean pressure (PAM), right atrial pressure (RAP), pulmonary vascular resistance (PVR), myocardial oxygen consumption (MVO2), and average peak velocity of coronary blood flow (APV) had mild significant increases as compared with controls. Nicotine significantly increased heart rate, mean arterial pressures, LVEDP, and pulmonary artery, pulmonary capillary wedge, and right atrial pressures. Nicotine increased dP/dt (2,062-3,188; p < 0.006) and decreased APV (9 to 8; p < 0.03). Combined ethanol followed by nicotine had synergistic increase in HR, SD, MAP, LVS, LVEDP, pulmonary pressures, CO, SV, dP/dt (2,184 > 5,206; p < 0.005), MVO2, and LVMW. However, the excitatory effects of nicotine were attenuated when ethanol was administered after nicotine (dP/dt, reduced from 2,058 to 1,653; p < 0.04, and APV increased from 10 to 12; p < 0.02). We conclude that ethanol increased APV but had nonsignificant effects on the hemodynamics, whereas nicotine reduced the APV and had significant excitatory responses. In combination (i.v.), ethanol + nicotine produced significant synergistic excitatory effects. On the other hand, the nicotine + ethanol combination increased APV and caused attenuation of the excitatory effects of nicotine in dogs.

Usefulness of left atrial abnormality for predicting left ventricular hypertrophy in the presence of left bundle branch block

The objective of this study was to identify left atrial (LA) abnormality on the electrocardiogram and other related variables as predictors of left ventricular (LV) hypertrophy in the presence of left bundle branch block (LBBB). In the presence of complete LBBB, the diagnosis of electrocardiographic abnormalities is problematic and that of LV hypertrophy remains difficult. The usual electrocardiographic criteria applied for the diagnosis of LV hypertrophy may not be reliable in the presence of LBBB. Therefore, noninvasive criteria will help physicians diagnose LV hypertrophy with electrocardiography. LA abnormality on the electrocardiogram was assessed by 2 independent observers as predictor of LV hypertrophy in the presence of LBBB in 120 patients, and data were compared with those of 100 patients without LA abnormality. LV mass was calculated from echocardiographic data. Besides LA abnormality, the other variables studied for prediction of LV hypertrophy were gender, age, body surface area, body mass index, frontal axis, and QrS duration. Of the 6 criteria analyzed, the P terminal force was found to be the most common and consistent criterion to detect LA abnormality. LV hypertrophy was confirmed by echocardiographic determination of LV mass in both groups. Observers reliably differentiated between the hypertrophied and normal-sized left ventricle in the presence of LBBB by correlating LA abnormality with LV mass determined by echocardiography. Observer 1 detected LA abnormality in 89% and observer 2 in 84% of patients. False-positive results were present in 11% and 16%. The observers recognition of LA abnormality in the present study was 91%. The 2 observers showed a sensitivity of 81% and 79% and a specificity of 91% and 88%, respectively, when diagnosis of LV hypertrophy was determined. LV mass increased significantly and was diagnostic of LV hypertrophy in 92% of patients with LA abnormality. In the remaining 11 patients (8%), the LA abnormality was of marginal abnormal magnitude. Each 0.01-mV/s increase in LA abnormality gave an increase of 30 g of LV mass. LV mass was increased in 86% of patients when corrected by body surface area. LV hypertrophy in the presence of LBBB on electrocardiography was found in only 13 patients (10%) when the 6 frequently used conventional criteria for diagnosis of LV hypertrophy by electrocardiography were used. Regression analysis revealed LA abnormality to be a strong independent predictor of increased LV mass. Multivariate analysis also revealed age, body mass index, body surface area, frontal axis, and QrS duration to be significant predictors of LV mass. This noninvasive study correlates LA abnormality by electrocardiogram and LV hypertrophy with echocardiography to conclude that LA abnormality was significantly diagnostic of LV hypertrophy in the presence of LBBB. Age, body mass index, body surface area, frontal axis, and QrS duration were also significant predictors of LV mass.

Left Atrial Abnormality in Acute Myocardial Infarction

This study assessed left atrial abnormality by electrocardiogram as a predictor of left ventricular dysfunction during acute myocardial infarction. Hemodynamic, angiocardiographic, echocardiographic, and serial creatine kinase-MB studies revealed the electrocardiogram to be a significant predictor of location of acute myocardial infarction, prevalence of occlusive disease in coronary vessels, myocardial contractility, low ejection fraction, increased left ventricular end-diastolic pressure, and serial creatine kinase-MB.

Combined effects of caffeine and nicotine on cardiovascular hemodynamics in canine model.

The independent effects of caffeine and nicotine on cardiodynamics are well documented, but combined effects of both are not reported. Initially, in phase I, 18 experiments were performed to study the dose-response curve of both the drugs. In phases II and III, 13 mongrel dogs were subjected to 30 experiments. In phase II, caffeine, 5 mg/kg, was given i.v. followed by nicotine, 50 micrograms/kg, and in phase III, the sequence of drug administration was reversed to study the effects on hemodynamics. In phase II, caffeine did not show significant changes in all the cardiovascular parameters, but nicotine administration after caffeine produced marked significant synergistic excitatory effects: the rate of increase of the first derivative of left ventricular pressure (dP/dt) increased from 1,101 +/- 111 to 3,194 +/- 872 (p < 0.003). In phase III, nicotine significantly increased heart rate, mean arterial pressures; left ventricular end-diastolic pressure (LVEDP); and pulmonary artery, pulmonary capillary wedge, and right atrial pressures. Nicotine increased dP/dt (964 +/- 182 to 1,639 +/- 60 mm Hg/s; p < 0.004). The excitatory effects of nicotine were attenuated by administration of caffeine (dP/dt, 918 +/- 140 reduced to 715 +/- 144 mm Hg/s; p < 0.04). Caffeine and nicotine, alone, caused nonsignificant and significant increases in hemodynamics, respectively. In combination, caffeine + nicotine administration produced significant synergistic excitatory effects in dogs. On the other hand, the nicotine + caffeine combination caused attenuation by caffeine of the excitatory effects produced by nicotine.

Effects of Cocaine and alcohol alone and in combination on cardiovascular performance in dogs

Background: With the proliferation of cocaine abuse, increased incidence of catastrophic cardiovascular events such as angina pectoris, myocardial infarction, ventricular arrhythmias, or sudden death are reported. Many of these patients also drink alcohol before and after cocaine use, leading to a high frequency of simultaneous exposure to both the drugs. Cocaine and ethanols independent effects on cardiodynamics are well documented, but their combined effects on complete cardiovascular hemodynamics remain unknown. Are effects additive, synergistic, or antagonistic? Methods: Sixteen dogs were instrumented to pass cardiac catheters into right and left ventricles. After they recovered from the effects of anesthesia, experiments were performed. In phase I, 18 experiments (6 dogs) established the dose by dose response curve. In phase II and III, another 10 dogs, subjected to 30 experiments, were given i.v. cocaine followed by ethanol and vice versa to study their effects on hemodynamics and coronary flow reserve. Results: Phase I: doses of cocaine (2 mg/kg) and ethanol (400 mg/kg) were established. Phase II: cocaine increased heart rate, blood pressure and dP/dt but ethanol administered after cocaine attenuated these effects [first derivative of the left ventricular pressure (dP/dt)<2052±104 from 2614±110 mm Hg/sec; P<0.04)]. Phase III: alcohol mildly increased hemodynamic parameters. Cocaines administration as the second drug had synergistic excitatory effects (dP/dt>3300±160 from 2854±142 mm Hg/sec; P<0.004). Conclusion: Cocaine increased heart rate, blood pressure, and dP/dt but reduced CFR. Alcohol mildly increased the hemodynamic variables and CFR. Combined cocaine and alcohol attenuated the excitatory effects of cocaine significantly. A reversed drug combination (ie, alcohol then cocaine) generated synergistic excitatory effects on the cardiovascular system of the dogs.

Combined Effects of Caffeine and Alcohol on Hemodynamics and Coronary Artery Blood Flow in Dogs

Alcohol intake is often followed by coffee drinking because of the universal acceptance of its sobering effect. Such effects were found inconsistent on motor functions. However, it is common belief that caffeine will antagonize the intoxicating effects of alcohol. The independent actions of caffeine and alcohol are well documented, but combined effects of short-term administration are unknown. This experimental work was designed to study the effects due to short-term administration of caffeine and alcohol on the cardiovascular system. In phase I, 30 experiments were performed in our laboratories to study the dose-response curves of both the drugs. In phases II and III, 15 dogs were subjected to 30 experiments. In phase II, caffeine, 5 mg/kg, was given i.v., followed by ethanol, 400 mg/kg i.v., and in phase III, sequence of drug administration was reversed to study the effects on hemodynamics and coronary artery blood flow. Caffeine did not show significant changes in all the cardiovascular parameters, and ethanol administration caused nonsignificant increase in heart rate, mean arterial pressure, left ventricular systolic pressure, and left ventricular (LV) mechanical work and decrease in the maximal rate of first derivative of LV pressure, stroke volume, and systemic vascular resistance. Left ventricular end-diastolic, pulmonary artery mean and right atrial pressures, pulmonary vascular resistance, myocardial oxygen consumption, and as coronary flow reserve increased as compared with controls. Combined caffeine and alcohol had synergistic effects, but when the order of drug administration was reversed (i.e., alcohol was followed by caffeine), the effect was antagonistic.