The inhibitory effect of rosmarinic acid on overexpression of NCX1 and stretch- induced arrhythmias after acute myocardial infarction in rats

The incidence of arrhythmias is the main cause of high mortality after myocardial infarction (AMI). The aim of the present study was to determine whether the rosmarinic acid (RA) could reduce the stretch-induced arrhythmias (SIAs) related to overexpression of NCX1 after AMI. Adult male Sprague-Dawley rats were randomly allocated into six groups: Sham, MI (100 mg/kg of isoproterenol (Iso), subcutaneously, on two consecutive days), RA (30 mg/kg, orally, 14 days), and RA (10, 15 and 30 mg/kg, 14 days) + I. MI induction was performed on the 13th and 14th days of the study period. Forty-eight hours after the first injection of Iso, the parameters of hypertrophy, plasma levels of malondialdehyde (MDA) and lipid profile were evaluated. Using Langendorff apparatus, the isolated hearts were transiently stretched for 5 s with three different end-diastolic volumes (ΔV1to3 = 0.05, 0.1 and 0.2 mL). Cardiac function parameters were measured for 30 s, and ventricular arrhythmias were recorded for 3 min after each stretch. Finally, the levels of cardiac troponin-I and NCX1 mRNA expression were examined. The rats of MI group showed a significant increase in hypertrophy index, MDA, triglyceride and cholesterol (P < 0.001). Additionally, a marked impairment in cardiac parameters, an increase in the rates of SIAs and NCX1 expression, and a decrease in troponin-I (P < 0.001) were observed. RA at three doses especially 15 mg/kg strongly improved almost all the mentioned factors (P < 0.001). Our results confirm that RA pretreatment could prevent hypertrophia, arrhythmia and cardiac dysfunction following AMI which is associated with inhibition of lipid peroxidation and overexpression of NCX1.

[Variability of glycemia and ventricular rhythm disturbances in patients with chronic heart failure and type 2 diabetes mellitus]

Aim of this observational study was assessment of effect of variability of glycemia on ventricular ectopic activity in patients with chronic heart failure (CHF) and type 2 diabetes mellitus (n=80). According to study protocol 24-hour Holter ECG monitoring was carried out at baseline, and after 3 and 6 months. Measurements of blood glucose level were made at 8 points during ECG monitoring - before and in 2 hours after main meals, before bedtime and at 3 o'clock in the morning. In 20 patients continuous combined monitoring of ECG and of blood glucose level was carried out. During monitoring of ECG high grade ventricular arrhythmias were found in 42 patients (53%). Pronounced variations of blood glucose level (mean amplitude of glycemic excursion >5 mmol/L) were associated with 2.3 fold increase risk of ventricular arrhythmias (p=0.04). A conclusion was made that pronounced 24-hour variations of glucose level in blood was associated with elevation of ventricular ectopic activity. High 24-hour variability of glycemia appeared to be proarrhythmogenic factor in patients with CHF and concomitant diabetes.

Relationship between sex hormones and idiopathic outflow tract ventricular arrhythmias in adult male patients

Sex hormones and gender differences have been reported to be associated with the occurrences of ventricular arrhythmias. This study investigated the relationship between sex hormones and idiopathic outflow tract ventricular arrhythmias (IOTVA) in adult male patients. Serum sex hormonal levels, which include testosterone, estradiol, and progestogen, were measured by using commercially prepared immunoassay kits. The average count of premature ventricular contractions (PVCs) (number/24h) was assessed by 72h electrocardiographic monitoring. No differences were found in the levels of testosterone and progestogen between the IOTVA male patients and the control males (both P>0.05). However, the level of estradiol in the IOTVA male patients was significantly lower than that in the control males (P<0.05). A significant negative correlation was observed between the number of PVCs and the level of estradiol in the IOTVA male patients (r=0.702, P<0.05). The current study suggested that IOTVA might be associated with the reduction of estradiol level in adult male patients.

Increased Ventricular Ectopic Activity in Relation to C-Reactive Protein, and NT-Pro-Brain Natriuretic Peptide in Subjects With No Apparent Heart Disease

BACKGROUND

Subjects with frequent ventricular premature complexes (VPC) and no apparent heart disease make a heterogenic group with regard to prognosis. Some biomarkers have recently proved useful in risk stratification in different heart diseases. We examined prognostic impact of NT-Pro-brain natriuretic peptide (NT-Pro BNP), and C-reactive protein (CRP) in relation to frequent VPC in subjects with no apparent heart disease.

METHODS

Six hundred seventy-eight healthy subjects between 55 and 75 years of age with no history of cardiovascular disease were included in the study. All were tested with fasting laboratory testing and 48-hour ambulatory ECG monitoring. Frequent VPC was defined as VPC > or =30/hour.

RESULTS

In 56 subjects (8%) with frequent VPC the prognosis was much poorer compared to those without frequent VPC (Hazard ratio and 95% CI: 2.3;1.2-4.4, P = 0.01), after adjustment for conventional risk factors. In subjects with frequent VPC increased levels of CRP (above 2.5 microg/mL) was the only factor among the tested biomarkers, which was associated with a poor prognosis. Taking subjects without frequent VPC as reference, the hazard ratio and 95% CI for subjects with frequent VPC and increased CRP was 3.6;1.8-7.1, P = 0.0004, and for those with frequent VPC and normal CRP 0.8;0.2-3.5, P = 0.83, after correction for conventional risk factors.

CONCLUSIONS

Among middle-aged and elderly subjects with no apparent heart disease and frequent VPCs, a CRP value > or =2.5 microg/mL is associated with a significantly higher risk of death and acute myocardial infarction. These subjects deserve primary prevention measures and further work up for structural heart disease.

Chronic Hemodynamic Effects After Radiofrequency Catheter Ablation of Frequent Monomorphic Ventricular Premature Beats

INTRODUCTION

Radiofrequency catheter ablation (RFCA) of severely symptomatic monomorphic ventricular premature beats (VPBs) is reported to be a safe and effective treatment option. However, the chronic hemodynamic effects of these VPBs have not been precisely evaluated.

METHODS AND RESULTS

We sought to investigate chronic effects after decreasing the number of VPBs by RFCA. A total of 47 patients who had no underlying heart disease and frequent monomorphic VPBs, consisting of more than 10,000 beats per day (24,194 +/- 12,516 beats per day), were enrolled. Patients were treated with RFCA and followed up over 6 months as outpatients. Echocardiography and serum B-type natriuretic peptide (BNP) level were repeatedly checked before and after RFCA. In 38 patients, whose VPBs were dramatically decreased to less than 1,000 beats per day by successful RFCA, left ventricular (LV) end-diastolic dimension (LVEDd) and end-systolic dimension (LVESd) measured by echocardiography decreased significantly (LVEDd: 50 +/- 5 to 48 +/- 5 mm, P < 0.01; LVESd: 33 +/- 7 to 30 +/- 6 mm, P < 0.01) in association with improvement of BNP level (39.9 +/- 34.1 to 16.8 +/- 10.3 pg/mL, P = 0.0001). In nine patients, whose VPBs were treated unsuccessfully by RFCA or that recurred, LV dimensions and BNP level did not change during the follow-up period.

CONCLUSION

Significant improvement in LV dimensions and serum BNP level appeared to indicate that RFCA of VPBs ameliorated occult cardiac dysfunction induced by frequent VPBs.

Can n-3 PUFA reduce cardiac arrhythmias? Results of a clinical trial

Dietary n-3 polyunsaturated fatty acids (PUFA) derived from fatty fish or fish oil may reduce the incidence of lethal myocardial infarction and sudden cardiac death. This might be due to a prevention of fatal cardiac arrhythmias. So far, however, only few clinical data are available being adequate to define indications for an antiarrhythmic treatment with n-3 PUFA. In a randomized, double-blind, placebo-controlled study 65 patients with cardiac arrhythmias without coronary heart disease or heart failure were subdivided into 2 groups. One group (n = 33) was supplemented with encapsulated fish oil (3g/day, equivalent to 1g/day of n-3 PUFA) over 6 months. The other group (n = 32) was given 3g/day of olive oil as placebo. In the fish oil group a decrease of serum triglycerides, total cholesterol, LDL cholesterol, plasma free fatty acids and thromboxane B2 as well as an increase of HDL cholesterol were observed. Moreover, a reduced incidence of atrial and ventricular premature complexes, couplets and triplets were documented. Accordingly, higher grades of Lown's classification switched to lower grades at the end of the dietary period. No changes were seen in the placebo group. The data indicate an antiarrhythmic action of n-3 PUFA under conditions of clinical practice which might help to explain the reduced incidence of fatal myocardial infarction and sudden cardiac death in cohorts on a fish-rich diet or supplemented with n-3 PUFA. Further studies elucidating the possible link between the reduced incidence of cardiac arrhythmias and sudden cardiac death by dietary intake of n-3 PUFA are warranted.

Relationship Between Brain Natriuretic Peptide, Myocardial Wall Stress, and Ventricular Arrhythmia Severity

We previously demonstrated that the severity of arrhythmias is reflected by circulating brain natriuretic peptide (BNP) concentrations in patients without signs of congestive heart failure. In the present study, we evaluated the relationships between the severity of the arrhythmia, BNP concentration, and echocardiographic findings. The subjects consisted of 52 patients with ventricular premature contractions (VPC) but no manifestations of heart failure and no digoxin or beta-blocker therapy. Patients underwent Holter monitoring, plasma sampling for BNP measurement, and transthoracic echocardiography (TTE). We scored the motion of 16 left ventricular segments, deriving a wall-motion score index (WMSI) by totaling the scores and dividing by the number of segments scored. Twenty-three patients with Lown grade I to II arrhythmias constituted group A while group B consisted of 29 Lown III to IV patients. Group B had BNP concentrations triple those in group A (57.2 versus 18.1 pg/mL, P < 0.01). Left ventricular ejection fraction (LVEF) was similar in groups A and B (65.2% versus 62.1%, NS). Although left ventricular end-diastolic dimension (LVEDD) was normal in both groups, group B exhibited a larger LVEDD than group A (50 versus 46 mm, P < 0.005). The correlation (r) between BNP and interventricular septum thickness (IVST) was 0.27 (P = 0.013) in group A and 0.37 (P < 0.0001) in group B. Between BNP and posterior wall thickness (PWT), the correlation was 0.23 (P = 0.014) in group A versus 0.33 (P < 0.0001) in group B. The WMSI in group B was higher than in group A (1.34 versus 1.11, P < 0.05). We believe that besides the changes in echocardiographic parameters, the BNP elevation in group B could be a response to abnormal wall stress from the severe ventricular arrhythmias.

Increasing plasma potassium with amiloride shortens the QT interval and reduces ventricular extrasystoles but does not change endothelial function or heart rate variability in chronic heart failure

OBJECTIVES

To test whether simply increasing plasma potassium with amiloride would exert any of the same beneficial effects on "surrogate outcome measures" that are seen with spironolactone. The latter has been shown to improve mortality in chronic heart failure, possibly as a result of improvements in endothelial dysfunction, vascular angiotensin converting enzyme (ACE), autonomic function, myocardial fibrosis, ventricular arrhythmias, and QT interval indices.

DESIGN

Randomised, placebo controlled trial.

SETTING

Teaching hospital.

PATIENTS AND INTERVENTIONS

Double blind crossover study involving 10 patients with New York Heart Association functional class II-III chronic heart failure comparing 5 mg/day amiloride (one month) with placebo.

MAIN OUTCOME MEASURES

Endothelial function, vascular ACE, collagen markers, 24 hour ECG, and QT interval results.

RESULTS

The amiloride induced increase in serum potassium (0.4 mmol/l) did not significantly change endothelial dysfunction, vascular ACE, collagen markers, or heart rate variability. However, amiloride significantly improved QT interval indices, reducing both QT dispersion (from 65.7 ms to 50.9 ms, p = 0.001) and mean maximal corrected QT (from 445 ms to 435 ms, p = 0.008). Amiloride also reduced ventricular extrasystoles (p < 0.05).

CONCLUSIONS

Amiloride shortens QT interval length and reduces ventricular extrasystoles in chronic heart failure, implying that this effect is caused by potassium retention per se. However, unlike spironolactone, amiloride did not improve endothelial dysfunction, vascular ACE, heart rate variability, or myocardial fibrosis, implying that spironolactone improves these latter effects by aldosterone blockade rather than by simply increasing serum potassium. Therefore, amiloride has fewer beneficial mechanistic effects than spironolactone, but it does share with spironolactone the ability to shorten the QT interval and reduce ventricular extrasystoles.

Effect of CYP2D6*10 genotype on propafenone pharmacodynamics in Chinese patients with ventricular arrhythmia

AIM

To determine the effect of CYP2D6*10 genotype on propafenone pharmacodynamics in Chinese patients with ventricular arrhythmia.

METHODS

Seventeen Chinese patients with ventricular premature contractions (VPC> or =1000/d) were recruited. They were normal in routine laboratory testing and administered propafenone hydrochloride 450-600 mg per day in three divided doses. Twelve lead cardiogram and 24 h Holter monitoring were performed before and after 7 d treatment of propafenone. Steady-state peak and trough concentrations of propafenone were measured by HPLC method. CYP2D6*10 genotypes of patients were assayed by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP).

RESULTS

Total inhibitory rate of VPC was 79.9 % in 17 patients with ventricular arrhythmia after propafenone treatment. PR interval prolongation was increased from 0.146 s+/-0.018 s to 0.161 s+/-0.022 s (P<0.05). CYP2D6 genotypes played an important role in plasma levels and effects of propafenone. In 450 mg/d group, patients with homozygous mutant of CYP2D6*10 not only had a Cmax of propafenone two times as high as those of wild-type genotype, but also showed a two fold higher inhibitory rate of VPC compared with those with homozygous CYP2D6*1 (P<0.05).

CONCLUSION

CYP2D6*10 genotype is relevant to decreased activity of CYP2D6 enzyme in Chinese patients. Elevated plasma concentration is consistent with better efficacy of propafenone in patients with ventricular arrhythmia.

Subclinical thyrotoxicosis and the heart

Subclinical thyrotoxicosis is defined as a below normal thyrotropin (TSH) in association with a normal total and free thyroxine (T4) and triiodothyronine (T3). It may be caused by thyroid hormone treatment or by endogenous thyroid disease. The degree of thyrotoxicosis may be estimated by the level of TSH suppression. Subclinical thyrotoxicosis may be associated with changes in cardiac performance and morphology, but this has not been consistently found in all patient populations. Changes may include increased heart rate, increased left ventricular mass index, increased cardiac contractility, diastolic dysfunction, and the induction of ectopic atrial beats or arrhythmias. Cardiac exercise performance may be impaired. Subclinical thyrotoxicosis should be treated in patients with cardiac symptoms or disease. Treatment may include reduction of the thyroid hormone dose, treatment of the underlying thyroid condition, or beta-blockers.

[Therapy of cardiac arrhythmias. Clinical significance of potassium- and magnesium aspartate in arrhythmias]

Potassium and magnesium deficiencies usually coexist and represent a risk factor for cardiac arrhythmias. Serum levels--in particular of magnesium--are inconclusive for establishing a possible electrolyte deficiency. Basic treatment of arrhythmia should therefore include the administration of potassium and magnesium, since the benefit is great, and the possible side effects is negligible. A placebo-controlled study involving patients with cardiac arrhythmias revealed that appreciably fewer ventricular asystoles occurred after three weeks of treatment with potassium and magnesium aspartate, even when serum levels were within the normal range prior to initiating treatment. Patients older than 50, and those with previous coronary heart disease and/or myocardial infarction derived particular benefit from this form of treatment.

CONCLUSION

These results underscore the key role played by potassium and magnesium in the treatment of cardiac arrhythmias.

Sex-specific triggers for right ventricular outflow tract tachycardia

BACKGROUND

Right ventricular outflow tract tachycardia (RVOT-VT) is a common arrhythmia in young patients without heart disease. The arrhythmia is characterized by repetitive bursts and premature ventricular contractions with a left bundle branch block, inferior-axis QRS morphology, and symptoms of palpitations. Although more frequent in women, sex-specific triggers for symptomatic RVOT-VT have not been identified.

METHODS AND RESULTS

We interviewed 34 women and 13 men referred for ablation of RVOT-VT to determine if predictable but sex-specific exacerbations in symptomatic RVOT-VT exist. After a general query asking if there was predictability to what triggered palpitations, we then specifically queried all patients about symptomatic RVOT-VT initiation with exercise, stress, caffeine, fatigue, and, in women only, periods of recognized hormonal flux. The times identified as states of hormonal flux included premenstrual, gestational, perimenopausal, and coincident with the administration of birth control pills. In response to the completed interview, the most common recorded trigger for RVOT-VT in women was recognized states of hormonal flux with 20 (59%) of 34 women responding positively and 14 (41%) of the 34 indicating that states of hormonal flux were the only recognizable triggers. Men were more likely than women to report that their RVOT-VT was predictably triggered by exercise, stress, or caffeine: 12 (92%) of 13 men versus 14 (41%) of 34 women (P <.01).

CONCLUSIONS

Triggers for RVOT-VT initiation are sex specific. Women have RVOT-VT initiation with recognized states of hormonal flux. Men more commonly have RVOT-VT initiated by exercise or stress. These data have important implications related to patient education and counseling in the setting of RVOT-VT and may influence the timing of drug treatment and electrophysiologic evaluation in selected patients.

[Distribution of Mg2+ and Ca2+ in serum and lymphocyte of the patients with arrhythmia]

The distributions of Mg2+ and Ca2+ in serum and lymphocyte from 51 arrhythmic patients (15 cases of atrial premature beat, 12 cases of atrial fibrillation, 24 cases of ventricular premature beat) and 30 healthy subjects were detected by flame atomic absorption spectrophotometry. The results showed that the distribution of Mg2+ of the arrhythmia cases was significantly lower than that of the control group (P < 0.01) and the concentration of Ca2+ in lymphocytes of arrhythmia case group was significantly higher than that of the control group (P < 0.01). The above distribution of Mg2+ and Ca2+ was somewhat related to the degree of heart failure. It is suggested that the lower distribution of Mg2+ in lymphocytes may cause arrhythmias.

Potassium concentrations and ventricular ectopy: a prospective, observational study in post-cardiac surgery patients

OBJECTIVE

To determine whether a correlation exists between concentrations of intracellular and extracellular potassium and to determine the frequency of ventricular ectopy in patients after cardiac operations.

DESIGN

Prospective, observational clinical evaluation.

SETTING

Surgical-respiratory intensive care unit of a university-affiliated tertiary care center.

PATIENTS

Continuous 24-hr electrocardiographic monitoring was performed, and serum (extracellular) and erythrocyte (intracellular) potassium concentrations ([K+]e and [K+]i) were determined, before cardiopulmonary bypass, immediately postoperatively, and at 2, 4, 12, and 20 hrs after elective coronary bypass grafting in 31 patients.

INTERVENTIONS

None. Potassium replacement was left to the discretion of the attending physicians.

MEASUREMENTS AND MAIN RESULTS

Although the mean [K+]e varied significantly during the postoperative 24-hr period (p<.0001), the [K+]i did not (p = .953). No significant correlations were found between premature ventricular beats and [K+]i, [K+]e, or [K+]i/[K+]e (all p>.05). However, among the few patients who had one or more episodes of ventricular tachycardia (VT) within 30 mins of a study K+ sample, the mean [K+]e was significantly lower during the episode(s) of VT compared with the mean [K+]e in the absence of VT (p<.01).

CONCLUSIONS

Although it is clear that over the clinically acceptable range of [K+]e and [K+]i concentrations seen in this population, there is no correlation between potassium concentrations and the occurrence of premature ventricular beats, the infrequent association of more serious ventricular ectopy, VT, with lower [K+]e concentrations supports the practice of using serum potassium to guide potassium replacement in patients after cardiac operations.

[Relationship between plasma hormones and ventricular premature contractions in extracorporeal shock wave lithotripsy--significance of human atrial natriuretic peptide (hANP)]

Extracorporeal shock wave lithotripsy (ESWL) is a safe and effective treatment for upper urinary tract stones. However, the mechanism by which this treatment may be involved in causing ventricular premature contractions (VPC) is unknown. We evaluated the relationship between VPC and plasma hormones in patients treated by ESWL. Holter monitoring was performed on 61 outpatients undergoing ESWL with electrocardiographic synchronization for upper urinary tract stones. The levels of cathecolamine, plasma renin activity (PRA), plasma aldosterone concentration (PAC), and human atrial natriuretic peptide (hANP) were measured before, immediately after, and 7 days after ESWL. Systolic blood pressure increased significantly immediately after, and decreased 7 days after ESWL. VPC occurred during 23 treatments (37.7%) but during ESWL no significant relationship was observed with the treatment side or location. Epinephrine increased significantly immediately after ESWL. hANP increased significantly immediately after ESWL, and decreased 7 days later. VPC occurred in all patients who had an hANP value above 40 pg/ml before ESWL. These results suggest that VPC is related to hemodynamic changes, and that hANP can predict VPC during ESWL.

Association of fasting plasma free fatty acid concentration and frequency of ventricular premature complexes in nonischemic non-insulin-dependent diabetic patients

We investigated the association between free fatty acid (FFA) concentration and ventricular premature complexes (VPCs) in nonischemic patients with non-insulin-dependent diabetes mellitus using 3 approaches: cross-sectional analysis (n = 142), intervention including induction of elevated FFA levels with Intralipid heparin (n = 15), and reduction in FFA levels with Acipimox (n = 34) and a longitudinal follow-up study (n = 59). Patients at the third tertile of fasting plasma FFA concentration had the strongest increase in VPCs. Independently of age, sex, body mass index (BMI), waist/hip ratio, left ventricular mass index, glycated hemoglobin, fasting plasma insulin and triglyceride concentration, and daily physical activity, FFA concentration and VPCs were significantly correlated (r = 0.21 p <0.01). At multiple logistic regression analysis independently of age, sex, BMI, waist/hip ratio, left ventricular mass index, mean arterial blood pressure, glycated hemoglobin, fasting plasma insulin, triglycerides and potassium concentration, fasting plasma low-density lipoprotein/high-density lipoprotein cholesterol ratio, and daily physical activity, plasma FFA concentration was a significant determinant of VPCs (odds ratio 1.2, 95% confidence interval 1.0 to 2.3). Intralipid infusion (10% in 24 hours) (n = 15) and acipimox administration (250 mg, 4 times/day) (n = 34) increased, and decreased fasting plasma FFA concentration, respectively. In those studies, change in VPCs paralleled the effects on plasma FFA. In the longitudinal study (n = 59), plasma FFA concentration predicted the development of VPCs (RR 1.4 95% confidence interval 1.0 to 1.9) independently of age, sex, BMI, waist/hip ratio, left ventricular mass index, mean arterial blood pressure, fasting plasma triglyceride concentration, fasting plasma low-density lipoprotein/high-density lipoprotein cholesterol ratio, and daily physical activity. In conclusion, in nonischemic patients with non-insulin-dependent diabetes mellitus, plasma FFA concentration is associated with the frequency of ventricular premature complexes.

Caffeine restriction has no role in the management of patients with symptomatic idiopathic ventricular premature beats

OBJECTIVE

To assess the role of caffeine restriction in the management of patients with symptomatic idiopathic ventricular premature beats.

DESIGN

A randomised, double blind, 6 week intervention trial incorporating dietary caffeine restriction, caffeinated coffee, and decaffeinated coffee.

SETTING

Cardiac outpatient clinic.

PATIENTS

13 patients with symptomatic frequent idiopathic ventricular premature beats.

MAIN OUTCOME MEASURES

Weekly measures of serum caffeine concentration, coffee consumption, visual analogue score of palpitations, and 24 hour ventricular premature beat frequency.

RESULTS

The interventions achieved significant alterations in serum caffeine concentrations (P < 0.001) which correlated with coffee consumption (r = 0.70; P < 0.001). Visual analogue palpitation scores showed a small, but significant correlation with ventricular premature beat frequencies (r = 0.34; P = 0.003). However, there were no significant changes in palpitation scores or ventricular premature beat frequencies during the intervention weeks and no significant correlations were found between these variables and serum caffeine concentrations.

CONCLUSIONS

Caffeine restriction has no role in the management of patients referred with symptomatic idiopathic ventricular premature beats.

[The reduction of beta-adrenoceptor density and the suppression of ectopic ventricular activity with low doses of amiodarone]

In 5 patients with frequent premature ventricular ectopic beats, refractory to other antiarrhythmic treatments, amiodarone, given orally at the dose of 200 mg once a day for 4 weeks, reduced beta-adrenoceptor density from 202.9 +/- 62 to 101.1 +/- 33 fmol/mg protein (p < 0.01). Similarly, kd decreased from 21.0 +/- 6 to 3.9 +/- 1 (p < 0.05). Changes in beta-adrenoceptor population were accompanied by a marked reduction in mean premature ventricular complexes (PVC) frequency from the control value of 428.9 +/- 150.3 to 13.4 +/- 10.7 PVC/h (p < 0.05) and by a decrease in heart rate, from 83.8 +/- 4 to 73.9 +/- 4 b/min (p < 0.01). On the contrary, mean arterial pressure remained unchanged. Patients did not show side effects during treatment. Therefore, low dose oral amiodarone has important pharmacologic and therapeutic effects. It significantly reduces lymphocyte beta-adrenoceptor density and is effective in treatment of ventricular arrhythmias. Additional studies were performed in vitro exposing lymphocytes to increasing concentrations of amiodarone. The analysis of variance for repeated measures showed that amiodarone-induced reduction in lymphocyte beta-adrenoceptor density is a dose-depending phenomenon. Accordingly, treatment with doses of amiodarone higher than that used in the present study may induce a major reduction in lymphocyte beta-receptor density and exert a depressant cardiac effect.