Suppression of sustained ventricular tachyarrhythmias: a comparison of d,l-sotalol with no antiarrhythmic drug treatment.

OBJECTIVES: This study evaluates the clinical efficacy of d,l-sotalol in patients with sustained ventricular tachyarrhythmias. BACKGROUND: D,l-sotalol is an important antiarrhythmic agent to prevent recurrences of sustained ventricular tachyarrhythmias (VT/VF). However, evidence is lacking that an antiarrhythmic agent like d,l-sotalol can reduce the incidence of sustained ventricular tachyarrhythmias in comparison to no antiarrhythmic drug treatment. METHODS: A prospective study was performed in 146 consecutive patients with inducible sustained ventricular tachycardia or ventricular fibrillation. In 53 patients, oral d,l-sotalol prevented induction of VT/VF during electrophysiological testing and patients were discharged on oral d,l-sotalol (sotalol group). In 93 patients, VT/VF remained inducible and a defibrillator (ICD) was implanted. After implantation of the device patients were randomly assigned to oral treatment with d,l-sotalol (ICD/sotalol group, n=46) or no antiarrhythmic medication (n=47, ICD-only group). RESULTS: During follow-up, 25 patients (53.2%) in the ICD-only group had a VT/VF recurrence in comparison to 15 patients (28.3%) in the sotalol group and 15 patients (32.6%) in the ICD/sotalol group (p=0.0013). Therapy with d,l-sotalol, amiodarone or metoprolol was instituted in 12 patients (25.5%) of the ICD-only group due to frequent VT/VF recurrences or symptomatic supraventricular tachyarrhythmias. In nine patients, 17% of the sotalol group, an ICD was implanted after VT/VF recurrence, three patients (5.7%) received amiodarone. Total mortality was not different between the three groups. CONCLUSIONS: D,l-sotalol significantly reduces the incidence of recurrences of sustained ventricular tachyarrhythmias in comparison to no antiarrhythmic drug treatment.

Long-term reproducibility of electrophysiologically guided therapy with sotalol in patients with ventricular tachyarrhythmias.

OBJECTIVES: Goal of this study was to assess the long-term reproducibility of electrophysiologic drug testing in patients with ventricular tachyarrhythmias (VT/VF). BACKGROUND: Programmed ventricular stimulation (PVS) is still widely used to guide antiarrhythmic therapy in patients with sustained ventricular tachycardia/fibrillation (VT/VF). Sotalol is considered as one of the most effective drugs for VT/VF. Because there is no proof of long-term reproducibility of a successful drug test with sotalol, we investigated the long-term reproducibility of drug testing with sotalol. METHODS: Thirty patients with VT/VF (age: 57+/-11 years, 20 patients with coronary heart disease, 7 patients with no structural heart disease, 3 with others) and reproducible induction of VT/VF (28 patients VT, two patients VF) in a baseline PVS, were suppressible with sotalol (mean dosage 395+/-137 mg) in a subsequent PVS. After a mean follow-up of 13+/-10 months a PVS was again performed in patients, who had no evidence of progressive cardiac disease, who did not experience any arrhythmia recurrences or who were drug compliant. Irrespective of the inducibility after long-term therapy with sotalol, all patients were kept on the initial sotalol regimen. All 30 patients had a stable cardiac condition, were free of VT/VF recurrences and were drug compliant. RESULTS: Despite the clinical efficacy of sotalol, in 12 patients (40%) VT/VF could again be induced after 13+/-10.2 months. Inducibility was independent of age, heart disease, ejection fraction and follow-up time. During a further follow-up of 22.1+/-10.9 months, five patients experienced nonfatal VT recurrences independently of the prior inducibility. CONCLUSIONS: This study shows a lacking long-term reproducibility of an initial effective PVS with sotalol. Despite an uneventful clinical follow-up, late electrophysiologic testing showed a VT/VF inducibility in a high portion of patients. Hence, electrophysiologic testing performed late after the initial drug test may no longer be predictive of outcome.

Ionic mechanisms of electrical remodeling in human atrial fibrillation.

OBJECTIVES: Atrial fibrillation (AF) is associated with a decrease in atrial ERP and ERP adaptation to rate as well as changes in atrial conduction velocity. The cellular changes in repolarization and the underlying ionic mechanisms in human AF are only poorly understood. METHODS: Action potentials (AP) and ionic currents were studied with the patch clamp technique in single atrial myocytes from patients in chronic AF and compared to those from patients in stable sinus rhythm (SR). RESULTS: The presence of AF was associated with a marked shortening of the AP duration and a decreased rate response of atrial repolarization. L-type calcium current (ICa,L) and the transient outward current (Ito) were both reduced about 70% in AF, whereas an increased steady-state outward current was detectable at test potentials between -30 and 0 mV. The inward rectifier potassium current (IKI) and the acetylcholine-activated potassium current (IKACh) were increased in AF at hyperpolarizing potentials. Voltage-dependent inactivation of the fast sodium current (INa) was shifted to more positive voltages in AF. CONCLUSIONS: AF in humans leads to important changes in atrial potassium and calcium currents that likely contribute to the decrease in APD and APD rate adaptation. These changes contribute to electrical remodeling in AF and are therefore important factors for the perpetuation of the arrhythmia.

Late outcome of survivors of idiopathic ventricular fibrillation.

This report describes clinical, hemodynamic, and electrophysiologic characteristics of 18 consecutive survivors of sudden cardiac arrest due to idiopathic ventricular fibrillation (VF) between 1986 and 1996. Long-term data in relation to the prescribed therapy are presented. The mean age of the 18 patients was 48 +/- 14 years (median 49). Electrophysiologic studies showed a low inducibility of sustained ventricular tachyarrhythmias in 4 patients (22%). Treatment consisted of class III agents, beta blockers, or implantable cardioverter-defibrillators. Two patients were discharged without any therapy. Therapy control was undertaken either by serial drug testing or by the empirical approach. Serious complications of therapy occurred in 2 patients: 1 patient experienced a proarrhythmic effect of antiarrhythmic drug therapy, and the other patient received multiple inadequate defibrillator discharges due to a defect in the transvenous lead. All but 1 patient (94%) remained free of recurrences of sudden cardiac arrest during a follow-up time of 45 +/- 29 months (median 41). One patient died 2 weeks after surviving cardiac arrest due to intractable VF while receiving sotalol treatment. Therapy guided by electrophysiologic studies did not have any impact on survival. Adverse effects or noncompliance led to discontinuation of drug therapy in 7 patients after a mean period of 31 +/- 30 months. Without any treatment 9 patients remained without recurrences over 45 +/- 33 months. Because of the absence of risk factors for arrhythmia recurrence and criteria to select therapy, randomized prospective studies are warranted to assess the optimal therapies in these young, ostensibly healthy patients.

Atrial fibrillation in coronary artery disease.

To answer whether atrial ischemia plays an important role in the genesis of atrial fibrillation in patients with coronary artery disease, we analyzed the electrocardiograms obtained at the time of coronary angiography and left ventriculography in 3220 consecutive patients. Atrial fibrillation was found in 74 (2.3%). Among those with significant coronary artery disease were 49 (66.2%) patients with atrial fibrillation and 88.5% with sinus rhythm (P<0.02). Angiograms of patients with atrial fibrillation and significant (>50%) coronary stenosis were re-evaluated and results compared to the control group which consisted of 108 consecutive patients who were in sinus rhythm at the time of coronary angiography. There were no differences between groups with respect to either frequency of injury to the right coronary artery and circumflex branch of left coronary artery or localization of the injury to this region (before or after atrial branch take-off). But patients with atrial fibrillation significantly more often had heart failure (55.1% versus 18.5%, P<0.001) and three vessel disease (30.5% versus 20.4%, P=0.05) as well as mitral valve insufficiency (20.4% versus 10.2%, P<0.05). In conclusion, in patients with coronary disease, systolic heart failure may be more important than atrial ischemia in causing atrial fibrillation.

Electrophysiology and long-term efficacy of pentisomide in patients with supraventricular tachycardia.

The electrophysiologic effects of pentisomide were investigated after intravenous (5 mg/kg) and oral (900-1200 mg three times a day) application in 9 patients with drug refractory atrioventricular nodal tachycardia and 6 patients with orthodromic atrioventricular re-entrant tachycardia. Pentisomide did not change sinus cycle length, effective refractory period of the right ventricle and the atrioventricular node. AH, HV interval, effective refractory period of the right atrium, QRS duration and QTc duration were (p less than or equal to 0.01) increased. Tachycardia cycle length was only increased after intravenous application of pentisomide, antegrade effective refractory periods of the accessory pathways and shortest fully pre-excited R-R intervals during atrial fibrillation were increased after the oral treatment phase (p = 0.054). Intravenous pentisomide prevented tachycardia in 6/9 patients with atrioventricular nodal tachycardia and in 2/6 patients with atrioventricular re-entrant tachycardia. If intravenous pentisomide did not prevent induction of the tachycardia, oral pentisomide was not effective either. During long-term follow-up 2/7 patients with atrioventricular nodal tachycardia and 1/4 patient with atrioventricular re-entrant tachycardia had a recurrence. Long-term treatment with pentisomide had to be discontinued because of possible side effects in 2 patients. It is concluded, that the electrophysiological effects of pentisomide are similar to those of flecainide and propafenone.

Comparison of the efficacy of a subcutaneous array electrode with a subcutaneous patch electrode, a prospective randomized study.

The patch electrode and the array electrode are the two types of subcutaneous leads available as an adjunct to a transvenous lead system in patients with high defibrillation thresholds. A prospective randomized study was conducted in 30 consecutive patients comparing the efficacy and the long-term performance of a patch electrode with an array electrode. After determination of the defibrillation threshold for the transvenous lead alone, a subcutaneous patch or an array electrode was implanted in random order. Adding a patch electrode decreased the defibrillation threshold in seven out of 15 patients (47%) from 13.2+/-6.6 to 10.5+/-5.1 J (P<0.05). In 13 out of 15 patients (87%), the implantation of an array electrode caused a significant lowering of the defibrillation threshold from 15.4+/-6.6 to 8.2+/-5.0 J (P<0.0001). The array electrode was significantly more effective in lowering the defibrillation threshold than the patch electrode (P<0.01). Complications during follow-up associated with the subcutaneous patch electrode were observed in four patients whereas no complications were associated with the array electrode (P<0.01). The additional implantation of an array electrode is more effective and associated with fewer complications compared to a patch electrode.

Variable responsiveness of anterograde and retrograde fast pathway conduction to adenosine in patients with typical AV-nodal reentry tachycardia.

Adenosine is known as a substance which depresses predominantly the slow pathway of the av-node. However, the effect of adenosine on the anterograde and retrograde fast pathway (FP) has not been studied in a large patient population. Ninety-one patients with inducible typical av-nodal reentrant tachycardias (AVNRT) were included. The clinically used dosage of 12 mg adenosine was administered subsequently as bolus injection during a constant atrial and ventricular pacing (500 ms) in all patients. Electrophysiological av-nodal parameters were determined. A higher responsiveness of the anterograde compared to the retrograde FP was observed: the majority of patients (76%) blocked anterogradely and 55% blocked retrogradely within the FP after the administration of 12 mg adenosine. Thirty-six percent of all patients revealed a differential behaviour to adenosine. Sixteen percent of all patients were completely resistant to adenosine (P=0.012). Electrophysiological parameters did not predict the responsiveness of the FP to adenosine. In patients with typical AVNRT the anterograde FP shows a higher sensitivity than the retrograde FP to adenosine. This might reflect an anatomical and/or functional distinction between anterograde and retrograde FP. The variable response to adenosine could be due to individual anatomical and electrophysiological heterogenity of the perinodal tissue and the av-node.

Effect of amiodarone and sotalol on the defibrillation threshold in comparison to patients without antiarrhythmic drug treatment.

AIM OF THE STUDY: It is generally accepted that chronic therapy with antiarrhythmic drugs might increase the defibrillation threshold at implantation of an implantable cardioverter defibrillator. A recently published animal study showed a minor effect of the class 1 antiarrhythmic drug lidocaine on the defibrillation threshold if biphasic shocks were used. METHODS AND RESULTS: We therefore performed a retrospective analysis in 89 patients who received an ICD capable of monophasic (n=18) or biphasic (n=71) shocks with a transvenous lead system. In all patients the defibrillation threshold was determined according to the same step down protocol. In the 18 patients with a monophasic device the effects of chronic therapy with amiodarone (n=7) on the defibrillation threshold were evaluated in comparison to a group without antiarrhythmic treatment (n=11). In those patients receiving a biphasic device the effects of chronic therapy with amiodarone (n=29), sotalol (n=20) or no antiarrhythmic medication (n=22) on the defibrillation threshold were evaluated. The groups receiving a monophasic device did not differ in respect to age, sex, underlying cardiac disease, clinical arrhythmia (VT/VF), clinical functional status, left ventricular ejection fraction and the number of patients with additional subcutaneous electrodes. These parameters as well as the type of implanted device were not different between patient groups receiving a biphasic device. Patients on chronic amiodarone therapy receiving a monophasic device had a significantly higher defibrillation threshold (29.1 +/- 8.8 J) than patients without antiarrhythmic treatment (19.1 +/- 5.1 J, P = 0.021). The groups did not differ significantly in respect to the impedance measured at the shocking lead (P = 0.13). In three patients on chronic amiodarone an epicardiac lead system had to be implanted due to an inadequate monophasic defibrillation threshold compared to no patient without antiarrhythmic drug treatment (P = 0.043). In the patients with a biphasic device the intraoperative defibrillation threshold was not significantly different between the three study groups (P = 0.44). No patient received an epicardiac lead system. The defibrillation threshold in the amiodarone group was 15.3 +/- 7.3 J, in the sotalol group 14.4 +/- 7.2 J and in the patients without antiarrhythmic drug treatment 17 +/- 6.1 J. As well, no significant difference was seen between the groups in respect of the impedance of the high voltage electrode (P = 0.2). CONCLUSION: With the use of a biphasic device in combination with a transvenous lead system the intraoperative defibrillation threshold is not significantly different between patients on chronic amiodarone in comparison to patients without antiarrhythmic drug treatment or patients on chronic oral sotalol. This is in contrast to our findings with a monophasic device.

[Visualization of pulmonary vein stenosis after radio frequency ablation for treatment of atrial fibrillation using multidetector computed tomography with retrospective gating]. / Darstellung von Pulmonalvenenstenosen nach Radiofrequenzablation zur Behandlung von Vorhofflimmern unter Verwendung der Multidetektor Computertomographie mit retrospektivem Gating.

PURPOSE: With the number of radio frequency ablations (RFA) for treatment of chronic atrial fibrillation increasing, the diagnostic evaluation for RFA associated pulmonary vein stenosis is getting more important. This study investigates the feasibility of the visualization of pulmonary vein stenosis using non-invasive multidetector computed tomography. MATERIALS AND METHODS: Twenty-eight patients were examined following RFA-treatment. A 4-slice (20 patients) and a 16-slice (8 patients) multidetector CT scanner (SOMATOM Volume Zoom and Sensation 16, Siemens, Forchheim, Germany) with retrospective gating was used to assess the pulmonary veins. Lesion severity was determined on a semi-quantitative scale (< 30 %, 30 - 50 %, > 50 %). RESULTS: CT was performed without any complications in all patients. Diagnostic image quality could be obtained in all examinations. The pulmonary veins showed lesions < 30 % in four patients, lesions of 30 -, 50 % in five patients and a stenosis > 50 % in one patient. Eighteen patients showed no lesions. CONCLUSION: Multidetector CT of the pulmonary veins seems to be able to visualize high-grade and low-grade lesions, but larger catheter-controlled studies are needed for further assessment of the diagnostic accuracy and clinical reliability of this noninvasive method.

Manifestation of severe coronary heart disease after anabolic drug abuse.

Anabolic steroids are frequently abused, thus increasing the risk of cardiovascular disease, despite the known unfavorable influence on lipid profiles. We report on a young bodybuilder who presented with ventricular tachycardia as the first manifestation of severe underlying coronary heart disease. Coronary angiogram revealed severe stenotic lesions in the right coronary artery and the left descending coronary artery, and hypokinetic regions corresponded to posterolateral and anterior myocardial infarctions. This young patient had a history without any coronary risk factors, but with a 2-year abuse of the anabolic steroid stanazolol. No report published so far has shown possible atherogenic consequences of long-term abuse of stanazolol.

High variability of retrograde fast pathway sensitivity to adenosine.

BACKGROUND: Adenosine is widely used as a tool to assess the effectiveness of radiofrequency ablation of concealed accessory pathways. HYPOTHESIS: The goal of this study was to determine the reliability of this test by studying the retrograde fast pathway sensibility in a large patient population with typical atrioventricular (AV) nodal reentry tachycardias. We sought also to determine whether AV nodal properties were predictive of a retrograde fast pathway sensitivity to adenosine. METHODS: In all, 124 patients with inducible AV nodal reentrant tachycardia were included in this study. All patients received a clinically used standard dose of 12 mg adenosine during ventricular pacing, with 500 ms and a constant ventriculoatrial (VA) conduction via the fast pathway. Electrophysiologic parameters of the AV node were determined in all patients in order to correlate them with the adenosine sensitivity of the retrograde pathway. RESULTS: In 74 patients, the injection of 12 mg adenosine resulted in a transient VA block, whereas no VA block occurred in the remaining 50 patients. In two patients, concealed accessory pathways were unmasked after the injection of adenosine. The adenosine sensitivity of the retrograde fast pathway was associated with longer retrograde conduction times and cycle lengths during AV nodal reentrant tachycardias. CONCLUSION: This study shows a high variability of retrograde fast pathway sensitivity to adenosine. Thus, in 40% of patients the lack of VA block after adenosine injection is not specific for persistent accessory pathway function after radiofrequency ablation. Electrophysiologic properties of patients with AV nodal reentrant tachycardias were different in patients with and without adenosine-sensitive retrograde fast pathways, possibly indicating differential patterns of penetration of the retrograde fast pathway into the compact AV node.

Tricuspid valve endocarditis due to a jet lesion detected by echocardiography in a 27-year old man with congenital ventricular septal defect.

The case of an non-addict young caucasian with isolated tricuspid valve endocarditis in congenital ventricular septal defect (VSD) is presented. Despite antibiotic treatment the patient suffered from recurrent right sided pneumonias. A computed tomography of the chest revealed an abscess localized in the right lower lung with signs of cavitation. Echocardiography identified a vegetation located at the anterior tricuspid leaflet due to a jet lesion through the VSD. ECG-gated MRI revealed normal left ventricular function and localized the septal defect and a jet against the anterior tricuspid valve leaflet. The patient underwent open heart surgery and the VSD was closed. Now, two years later, the patient is free from any symptoms or complications. This case illustrates that noninvasive techniques like echocardiography and ECG-gated MRI can not only accurately image cardiac anatomy in patients with ventricular septal defect but additionally provide information about the pathomechanism of the development of jet lesions resulting in valvular vegetations. Operative correction of underlying cardiac disease in nonaddicts with complicating tricuspid valve endocarditis might be a favourable treatment especially when antibiotic treatment fails to cure the infection.

Quantitation of pentisomide and its metabolite by high-pressure liquid chromatography in human serum.

A rapid, inexpensive, and accurate high-performance liquid chromatographic method for the simultaneous determination of pentisomide and its major mono-N-dealkylated metabolite has been developed. After a simple and inexpensive solvent extraction procedure, the unchanged drug, its metabolite, and the internal standard are separated using a C18 reversed-phase column with a 5-microns particle size. The eluent is monitored with ultraviolet detection at 260 nm. Endogenous substances or a variety of drugs do not interfere with the assay. The mean recoveries of pentisomide and its metabolite are 92.6% and 92.2%, respectively. The limit of detection of the assay is 28 ng/mL for both drugs. Serum levels of pentisomide and its metabolite in patients on oral therapy for supraventricular tachycardia are reported.

Experience with an ICD incorporating biventricular pacing.

Biventricular pacing for cardiac resynchronization is a promising therapy for symptomatic improvement in selected patients with underlying severe congestive heart failure. ICD treatment has been shown to prolong life in patients with life threatening ventricular tachyarrhythmias, but it does not improve quality of life. This review discusses current experience with ICD's incorporating biventricular pacing.

[Is intraoperative ICD-testing still necessary?]. / Ist die intraoperative ICD-Testung noch nötig?

Intraoperative ICD-testing is traditionally performed in many hospitals in order to ensure reliable sensing, detection, and defibrillation of induced ventricular fibrillation. The technical progress of defibrillators allows rapid detection and delivery of high energy shocks which defibrillates effectively in the vast majority all patients at implant. This review describes arguments pro and contra of systematic testing of the defibrillation threshold in all patients. Many reasons argue against testing in all patients: experimental considerations, patients' specific and nonspecific factors, e.g., underlying severity of cardiac disease, ischemia, and medication, as well as factors specific to the ICD system, e.g., implanted type and location of electrodes and active cans. Finally, the testing method is very important, since it bears the risk of false negative test results because the a priori probability of a positive test result is >95%. Therefore, data from prospective randomized studies are necessary in order to abandon the tradition of ICD-testing on an evidence-based background.

[Ventricular fibrillation in intra-atrial cardioversion of atrial fibrillation]. / Kammerflimmern bei intraatrialer Kardioversion von Vorhofflimmern.

Recently intra-atrial defibrillation has become an interesting alternative to external defibrillation and drug therapy for the treatment of atrial fibrillation. Low-energy intra-atrial defibrillation can be used to restore sinus rhythm f.ex. after a failed external cardioversion or during an electrophysiologic study when the administration of antiarrhythmic drugs should be avoided. Additionally this new technique has led to the development of implantable atrial defibrillators for the treatment of selected patients suffering from chronic atrial fibrillation. Intra-atrial defibrillation seems to be a highly effective and safe method, but little experience exists concerning the outcome so far. Especially the potential risk of inducing ventricular pro-arrhythmia is subject of current controversy. We report the case of a 79-year-old patient suffering from WPW syndrome with a concealed bypass tract who was subject to an intra-atrial defibrillation during an electrophysiologic study. At the beginning of the study atrial fibrillation could be converted to sinus rhythm by a single low-energy atrial defibrillation (3 J.). After a short period of time a second intra-atrial defibrillation had to be performed in the same way because of recurrent atrial fibrillation. By this atrial shock ventricular fibrillation was induced, so that high energy external defibrillation became necessary. Analyzing the ECG a correct R-wave synchronization was found, but a rather short preceding RR interval (252 ms). In conclusion, low energy atrial defibrillation is gaining importance as a highly effective new technique to restore sinus rhythm in patients suffering from atrial fibrillation resistant to conventional therapies. Nevertheless potential risks have to be considered such as the induction of ventricular pro-arrhythmia. Therefore, a correct R-wave synchronization is obligatory and shock delivery should be withheld after short RR intervals. Future prospective randomized studies will have to show whether this new technique is really safe enough and superior to the conventional methods for restoring sinus rhythm in patients suffering from atrial fibrillation.

[Administration of adenosine for termination of atrioventricular nodal reentry tachycardia: induction of atrial fibrillation with rapid conduction over an accessory pathway and unmasking of concomitant Wolff-Parkinson-White syndrome]. / Adenosingabe zur Terminierung einer atrio-ventrikulär-nodalen-Reentry-Tachykardie: Induktion von Vorhofflimmern mit schneller Uberleitung bei Demaskierung eines konkomitierenden Wolff-Parkinson-White-Syndroms.

The antiarrhythmic properties of adenosine, its ultra-short half-life and the absence of frequent serious side effects make it a front-line agent in arrhythmia management, especially in the treatment of atrioventricular nodal reentrant tachycardia. Due to a shortening of atrial refractoriness, adenosine can facilitate the induction of atrial fibrillation. Life threatening tachycardias may result from a potential rapid conduction of atrial fibrillation over an accessory pathway especially if the latter one has a short antegrade refractory period. We report a case of a 59 year old female patient in which intravenous administration of adenosine during typical atrioventricular nodal reentrant tachycardia was followed by atrial fibrillation with rapid conduction over a hitherto unknown accessory pathway. After intravenous administration of adenosine the tachycardia was terminated successfully within 38 s. After a short period of asystole, spontaneous atrial fibrillation developed unmasking an antegrade preexcitation with subsequent rapid ventricular response (210 b/min). The three-lead ECG showed a narrow QRS complex tachycardia. Because of spontaneous conversion to sinus rhythm and the absence of hemodynamic compromise there was no need for external cardioversion. During electrophysiological study an antidromic atrioventricular reentrant tachycardia was recorded over a left posteroseptal accessory pathway including antegrade conduction properties only. Because of its ultrashort half-life, serious side effects after adenosine administration are rare. The possibility of life threatening proarrhythmias after intravenous adenosine administration should be taken into consideration if the etiology of a paroxysmal supraventricular tachycardia is not clear and a concomitant Wolff-Parkinson-White syndrome cannot be excluded. As with application of all intravenous antiarrhythmic agents, the administration of adenosine should only be performed if continuous ECG monitoring and cardioversion facilities are available and possible.