Effect of high doses of magnesium on converting ibutilide to a safe and more effective agent

Ibutilide is a class III antiarrhythmic agent indicated for cardioversion of atrial fibrillation and atrial flutter to sinus rhythm (SR). The most serious complication of ibutilide is torsades de pointes (TdP). Magnesium has been successfully used for the treatment of TdP, but its use as a prophylactic agent for this arrhythmia has not yet been established. The present study investigated whether high dose of magnesium would increase the safety and efficacy of ibutilide administration. A total of 476 patients with atrial fibrillation or atrial flutter who were candidates for conversion to SR were divided into 2 groups. Group A consisted of 229 patients who received ibutilide to convert atrial fibrillation or atrial flutter to SR. Group B consisted of 247 patients who received an intravenous infusion of 5 g of magnesium sulfate for 1 hour followed by the administration of ibutilide. Then, another 5 g of magnesium were infused for 2 additional hours. Of the patients in groups A and B, 154 (67.3%) and 189 (76.5%), respectively, were converted to SR (p = 0.033). Ventricular arrhythmias (sustained, nonsustained ventricular tachycardia, and TdP) occurred significantly more often in group A than in group B (7.4% vs 1.2%, respectively, p = 0.002). TdP developed in 8 patients (3.5%) in group A and in none (0%) in group B (p = 0.009). The administration of magnesium (despite the high doses used) was well tolerated. In conclusion, the administration of high doses of magnesium probably makes ibutilide a much safer agent, and magnesium increased the conversion efficacy of ibutilide.

[The study of inhibiting heart rate and rapidly terminating atrial flutter of ibutilide on canine]

OBJECTIVE

To observe the electrophysiological effects of ibutilide on canine and to explore the potential mechanisms of ibutilide on terminating atrial flutter.

METHODS

Eighteen mongrel dogs were anesthetized and intubated. The heart was exposed through thoracotomy for electrodes implantation. The electrophysiologic variables (heart rate, the conduction of intraatrium and interatrium, the conduction ratio of isthmus, the effective refractory period) were measured in the absence or presence of ibutilide (10 minute infusion with 0.10 mg/kg ibutilide, 30 minutes later with a maintaining dose of 0.01 mg/min).

RESULTS

Ibutilide significant suppressed sinus atrial node function, the peak effect was observed at 20 - 30 min post drug infusion and heart rate returned to normal at 2 hours post infusion. Post ibutilide infusion, 1 canine developed sinus pause for 5 seconds and 2:1 atrioventricular conduction block was evidenced in another canine. The atrial, ventricular and pulmonary vein effective refractory periods were all significant prolonged (all P < 0.05) post ibutilide infusion. However, conduction of intraatrium, interatrium and isthmus remained unchanged post ibutilide infusion (all P > 0.05).

CONCLUSIONS

Ibutilide could suppress sinus atrial node and the atrioventricular node function. The mechanism of ibutilide on rapidly terminating atrial flutter might be related to the prolongation of the refractory periods which might then result in the reduction of the whole excitable gap of the reentrant circuit and induce proceed inability of reentrant wavefront.

A case of myotonic dystrophy presenting with ventricular tachycardia and atrial fibrillation

Myotonic dystrophy type 1 (MD1) is an autosomal dominant disorder characterized by myotonia, progressive muscular weakness, cataract, and cardiac involvement. Cardiac involvement is common and includes conduction system abnormalities, supraventricular and ventricular arrhythmias, and less frequently, myocardial dysfunction and ischemic heart disease. A 54-year-old woman with a previous diagnosis of MD1 was admitted with palpitation, blood pressure of 157/118 mmHg, and a heart rate of 220 beats/min. Electrocardiography (ECG) showed ventricular tachycardia. Within minutes, hemodynamic collapse developed and electrical cardioversion was performed. Immediately following cardioversion, ECG showed atrial fibrillation, a slightly prolonged QT interval, and intraventricular conduction delay. After intravenous infusion of amiodarone, the rhythm converted to sinus. Transthoracic echocardiography showed significantly depressed left ventricular function, an ejection fraction of 25%, and normal coronary arteries. During electrophysiological study, atrium-His interval and His-ventricle interval were 120 msec was 54 msec, respectively, and monomorphic ventricular flutter was induced. An implantable cardioverter-defibrillator was placed. She was discharged in sinus rhythm.

Resolution of atrial thrombosis with heparin in a newborn with atrial flutter

Atrial thrombosis is a relatively rare event in children. We report a case of a newborn with AFI who after restoration of sinus rhythm, developed atrial thrombus on a prominent Chiari network floating between the right and left atrium through the patent foramen ovale. The thrombus was resolved following treatment with heparin without events.

CONCLUSION

Atrial stunning was proposed as a key mechanistic phenomenon because the thrombus occurred after the cardioversion of AFI to sinus rhythm. Heparin may be effective in the resolution of atrial thrombus within a few days.

[Next cardioversion or RF ablation in professional driver with recurrent typical atrial flutter and MAS syndromes]

We describe a 42-year-old professional driver with hypertension, obesity and recurrent episodes of highly symptomatic typical atrial flutter. Despite chronic sotalol treatment, 1:1 AV conduction with RBBB-morphology was observed. After excluding of thrombus in the heart chambers, the 'urgent' and successful RF ablation was performed.

Acute management of atrial fibrillation and atrial flutter in the critical care unit: should it be ibutilide?

BACKGROUND

Ibutilide is currently indicated for the rapid conversion of atrial fibrillation (Afb) or atrial flutter (Afl) of recent onset but limited to patients who are hemodynamically stable and without symptomatic cardiovascular conditions.

HYPOTHESIS

The study was undertaken to assess the efficacy and safety of ibutilide in patients with Afb or Afl associated with acute cardiovascular-medical disorders and in patients receiving prior selective antiarrhythmic drug therapy.

METHODS

The study included 34 patients, mean age 75 +/- 16.3 years, with Afb (n = 25) or Afl (n = 9) having a variety of disorders, for example, congestive heart failure, unstable angina, borderline hypotension, respiratory failure, and chronic renal failure. Prior antiarrhythmic drugs consisted of propafenone (n = 5) or amiodarone (n = 3). Eligibility for cardioversion was established with appropriate anticoagulation or transesophageal echocardiography findings. Ibutilide was given as up to two 10 min infusions of 1 mg separated by 10 min.

RESULTS

The overall conversion rate after ibutilide was 79.4% (27/34 patients): 80% for Afb and 78% for Afl. More than 90% converted within 1 h of treatment. A high conversion rate of 92% resulted in those with an arrhythmia duration of < or = 1 week. All eight patients with prior antiarrhythmic therapy converted to sinus rhythm. The average baseline QTc interval for all patients increased 17.1% (397 +/- 63.3 to 465 +/- 60.2 ms) at 30 min. For eight patients (including four who received prior antiarrhythmic drugs), QTc interval prolongation > or = 500 ms was associated with nearly half the entire incidence of arrhythmic events. Proarrhythmia, the exclusive adverse effect, consisted of ventricular extrasystoles (n = 10) and nonsustained monomorphic ventricular tachycardia (VT) (n = 2) managed with intravenous MgSO4, and sustained polymorphic VT (n = 1) requiring electrical cardioversion.

CONCLUSION

Ibutilide is an effective and well tolerated drug for the rapid termination of Afb or Afl of recent onset associated with symptomatic and/or hemodynamically unstable disorders, and it is most efficacious (> or = 90%) when the atrial arrhythmia is < or = 1 week in duration. Proarrhythmic events are readily manageable in a monitored unit with access to appropriate treatment.

[Glass of water or ablation? - episodes of malignant atrial tachyarrhythmias during swimming in a lake in a woman with overt Wolff-Parkinson-White syndrome and benign palpitations for several decades of life]

We present a case of a 41 year old woman with overt Wolff-Parkinson-White syndrome (WPW) and benign palpitations for over four decades of life who suffered from a malignant atrial tachyarrhythmias (typical atrial flutter concomitant with left atrial fibrillation) during swimming in a lake. Loading dose of amiodarone increased frequency of attacks of sustained AVRT. In spite of treatment with amiodarone, effective refractory period of accessory pathway was still short. After ablation of accessory pathway, during five years of follow-up, there was no arrhytmia recureence.

A survey of thyroid function test abnormalities in patients presenting with atrial fibrillation and flutter to a New Zealand district hospital

AIM

Subclinical and overt hyperthyroidism is a known trigger of atrial fibrillation and flutter (AF). We wanted to see if thyroid function tests (TFT) were being requested appropriately in patients with atrial fibrillation or flutter at North Shore Hospital, and how common subclinical or overt hyperthyroidism was in our local inpatient population presenting with AF.

METHOD

Clinical data on 250 patients admitted to North Shore Hospital with a history of AF was retrospectively analysed, including prior history of thyroid dysfunction, measurement of TFT and their results at the time of admission, subsequent management of subjects with abnormal TFT, and the association of amiodarone treatment or use of radiocontrast with TFT derangements.

RESULTS

Of the 250 patients analysed, only a small (7.2%) proportion had known thyroid dysfunction prior to admission, most of whom had hypothyroidism on thyroxine replacement. Although the majority (77%) of AF patients had had TFT checked either at the time of admission or in the prior 6 months, a significant proportion (23%) had not. Of the patients in whom TFT were performed, 82% were normal. Abnormalities included subclinical hyperthyroidism (2.1%), overt hyperthyroidism (3.1%), subclinical hypothyroidism (11%), and overt hypothyroidism (1.6%).

CONCLUSION

Despite a relatively low frequency, hyperthyroid conditions in patients presenting to North Shore Hospital with AF were sufficiently prevalent to continue recommending TFT assessment in these patients. Although the majority of AF patients were being adequately screened with TFT, a significant proportion was not, and those with abnormalities were not well followed up.

[Proarrhythmic effect of propafenone in patients with atrial fibrillation and atrial flutter]

We present two cases of proarrhythmia after propafenone treatment. In the first case slowing of the flutter cycle length from 205 ms to 290 ms resulted in a change from well tolerated two to one atrioventricular conduction to one to one conduction with hypotension and presyncope. In the second case organization of atrial fibrillation to atypical atrial flutter and use-dependent left bundle branch block resulted in fast broad QRS tachycardia that mimicked ventricular tachycardia.

The usefulness of 99mTc-sestaMIBI thyroid scan in the differential diagnosis and management of amiodarone-induced thyrotoxicosis

BACKGROUND

Amiodarone-induced thyrotoxicosis (AIT) is caused by excessive hormone synthesis and release (AIT I) or a destructive process (AIT II). This differentiation has important therapeutic implications.

PURPOSE

To evaluate (99m)Tc-sestaMIBI (MIBI) thyroid scintigraphy in addition to other diagnostic tools in the diagnosis and management of AIT.

SUBJECTS AND METHODS

Thyroid and (99m)Tc-MIBI scintigraphies were performed in 20 consecutive AIT patients, along with a series of biochemical and instrumental investigations (measurement of thyrotrophin, free thyroid hormones and thyroid autoantibodies; thyroid colour-flow Doppler sonography (CFDS) and thyroid radioiodine uptake (RAIU)).

RESULTS

On the basis of instrumental and laboratory data (excluding thyroid (99m)Tc-MIBI scintigraphy) and follow-up, AIT patients could be subdivided into six with AIT I, ten with AIT II and four with indefinite forms of AIT (AIT Ind). (99m)Tc-MIBI uptake results were normal/increased in all the six patients with AIT I and absent in all the ten patients with AIT II. The remaining four patients with AIT Ind showed low, patchy and persistent uptake in two cases and in the other two evident MIBI uptake followed by a rapid washout. MIBI scintigraphy was superior to all other diagnostic tools, including CFDS (suggestive of AIT I in three patients with AIT II and of AIT II in three with AIT Ind) and RAIU, which was measurable in all patients with AIT I, and also in four out of the ten with AIT II.

CONCLUSION

Thyroid MIBI scintigraphy may be proposed as an easy and highly effective tool for the differential diagnosis of different forms of AIT.

Use of bisphosphonates among women and risk of atrial fibrillation and flutter: population based case-control study

OBJECTIVE

To assess the association between atrial fibrillation and flutter and use of bisphosphonates for osteoporosis among women.

DESIGN

Population based case-control study, using medical databases from Denmark.

SETTING

Northern Denmark.

PARTICIPANTS

13 586 patients with atrial fibrillation and flutter and 68 054 population controls, all with complete hospital and prescription history.

MAIN OUTCOME MEASURE

Adjusted relative risk of atrial fibrillation and flutter.

RESULTS

435 cases (3.2%) and 1958 population controls (2.9%) were current users of bisphosphonates for osteoporosis. Etidronate and alendronate were used with almost the same frequency among cases and controls. The adjusted relative risk of current use of bisphosphonates compared with non-use was 0.95 (95% confidence interval 0.84 to 1.07). New users had a relative risk of 0.75 (95% confidence interval 0.49 to 1.16), broadly similar to the estimate for continuing users (relative risk 0.96, 95% confidence interval 0.85 to 1.09). The relative risk estimates were independent of number of prescriptions and the position of the atrial fibrillation and flutter diagnosis in the discharge record, and were similar for inpatients and outpatients.

CONCLUSION

No evidence was found that use of bisphosphonates increases the risk of atrial fibrillation and flutter.

Amiodarone—Avoid the danger of Torsade de Pointes

We present two patients who had life-threatening arrhythmias, which are highly likely to be secondary to amiodarone. This class III anti-arrhythmic is commonly prescribed for the acute presentation of supra-ventricular and ventricular arrhythmias. However, occasionally its use can transform arrhythmias from benign to dangerous. These cases highlight the need for careful attention to the indications, cautions and contra-indications of amiodarone as well as the need for vigilance following initiation of anti-arrhythmic therapy.

Emergency department use of intravenous procainamide for patients with acute atrial fibrillation or flutter

OBJECTIVES

Acute atrial fibrillation and flutter are very common arrhythmias seen in emergency department (ED) patients, but there is no consensus for their optimal management. The objective of this study was to examine the efficacy and safety of intravenous (IV) procainamide for acute atrial fibrillation or flutter.

METHODS

This health records review included a consecutive cohort of ED patients with acute-onset atrial fibrillation or atrial flutter who received IV procainamide at one university hospital ED during a five-year period. The standard clinical protocol involved IV infusion of 1 g of procainamide over 60 minutes, followed by electrical cardioversion if necessary. A trained observer extracted data from the original clinical records. Outcome measurements included conversion to sinus rhythm, adverse events, and relapse up to seven days.

RESULTS

The 341 study patients had a mean age of 63.9 years (SD +/- 15.5 years), and 56.6% were male. The conversion rates were 52.2% (95% confidence interval = 47% to 58%) for 316 atrial fibrillation cases and 28.0% (95% confidence interval = 13% to 46%) for 25 atrial flutter cases. Mean dose given was 860.7 mg (SD +/- 231.2 mg), and median time to conversion was 55 minutes. Adverse events occurred in 34 cases (10.0%): hypotension, 8.5%; bradycardia, 0.6%; atrioventricular block, 0.6%; and ventricular tachycardia, 0.3%. There were no cases of torsades de pointes, cerebrovascular accident, or death. Most patients (94.4%) were discharged home, but 2.9% of patients returned with a recurrence of atrial fibrillation within seven days.

CONCLUSIONS

This study of acute atrial fibrillation or flutter patients treated in the ED with IV procainamide suggests that this treatment is safe and effective in this setting. Procainamide should be prospectively compared with other ED strategies.

Effect of nifekalant for acute conversion of atrial flutter: the possible termination mechanism of typical atrial flutter

BACKGROUND

Nifekalant is a class III antiarrhythmic drug, which is usually used for suppression of ventricular tachycardia (VT) and fibrillation. We studied the efficacy of nifekalant for acute conversion of atrial flutter (AFL) in a prospective, open label study in the intensive care unit (ICU) of cardiovascular medicine.

METHODS

This study consisted of 31 patients. Twenty-six patients (84%) suffered from structural heart diseases. AFL was developed in 15 patients (48%) while on antiarrhythmic therapy with class IA or IC drugs (I-AFL group) for suppressing atrial fibrillation (AF) and in the remaining patients without such drugs (S-AFL group). Patients with prolonged QT interval, hypokalemia were excluded. All patients received one dose of 0.3 mg/kg of nifekalant over 10 minutes under continuous ambulatory monitoring. Four patients with common AFL in each group received nifekalant during electrophysiologic (EP) study.

RESULTS

Nifekalant had an overall AFL conversion efficacy of 77.4% within 60 minutes. Eleven patients in S-AFL group (68.8%) and 13 patients in I-AFL group (86.7%) could be converted with mean conversion times of 10.8 +/- 6.2 and 15.0 +/- 8.0 minutes, respectively (n.s.). Conversion rate was significantly higher in patients with a short duration of arrhythmia. The two modes of AFL termination were mainly demonstrated and the preferential mode significantly differed between the two groups. One patient in each group with excessive QT prolongation (6.5%) developed torsade de pointes (TdP), requiring electrical shock in one patient (3.3%).

CONCLUSIONS

Nifekalant can be used for conversion of AFL with a potent efficacy even in patients with structural heart diseases. However, caution should be required for developing TdP.

Dronedarone for maintenance of sinus rhythm in atrial fibrillation or flutter

BACKGROUND

Amiodarone is effective in maintaining sinus rhythm in atrial fibrillation but is associated with potentially serious toxic effects. Dronedarone is a new antiarrhythmic agent pharmacologically related to amiodarone but developed to reduce the risk of side effects.

METHODS

In two identical multicenter, double-blind, randomized trials, one conducted in Europe (ClinicalTrials.gov number, NCT00259428 [ClinicalTrials.gov] ) and one conducted in the United States, Canada, Australia, South Africa, and Argentina (termed the non-European trial, NCT00259376 [ClinicalTrials.gov] ), we evaluated the efficacy of dronedarone, with 828 patients receiving 400 mg of the drug twice daily and 409 patients receiving placebo. Rhythm was monitored transtelephonically on days 2, 3, and 5; at 3, 5, 7, and 10 months; during recurrence of arrhythmia; and at nine scheduled visits during a 12-month period. The primary end point was the time to the first recurrence of atrial fibrillation or flutter.

RESULTS

In the European trial, the median times to the recurrence of arrhythmia were 41 days in the placebo group and 96 days in the dronedarone group (P=0.01). The corresponding durations in the non-European trial were 59 and 158 days (P=0.002). At the recurrence of arrhythmia in the European trial, the mean (+/-SD) ventricular rate was 117.5+/-29.1 beats per minute in the placebo group and 102.3+/-24.7 beats per minute in the dronedarone group (P<0.001); the corresponding rates in the non-European trial were 116.6+/-31.9 and 104.6+/-27.1 beats per minute (P<0.001). Rates of pulmonary toxic effects and of thyroid and liver dysfunction were not significantly increased in the dronedarone group.

CONCLUSIONS

Dronedarone was significantly more effective than placebo in maintaining sinus rhythm and in reducing the ventricular rate during recurrence of arrhythmia.

Atrial flutter: a focus on treatment options for a common supraventricular tachyarrhythmia

Atrial flutter (AFl), a re-entrant atrial tachycardia, is a cardiac rhythm disturbance that arises in the upper chambers of the heart. This usually non-life-threatening condition can be treated by a number of medical intervention strategies, which include electrical cardioversion, pharmacological therapy, and catheter ablation. These options have been available in clinical practice for a number of years. However, catheter ablation, in the form of radiofrequency catheter ablation and cryo catheter ablation, is increasingly utilised as a first-line treatment option for AFl in certain patients. The purpose of this review article is two-fold: first, to briefly present an overview of AFl and the more familiar treatment options for this arrhythmia, and second to provide more in-depth coverage of catheter ablation technologies as a treatment option for patients with AFl. As part of the latter objective, recent clinical studies documenting the use of radiofrequency catheter ablation and cryo catheter ablation for AFl are presented and their results briefly discussed.

The Safety and Efficacy of Ibutilide in Children and in Patients with Congenital Heart Disease

BACKGROUND

The safety and efficacy of ibutilide in the cardioversion of atrial flutter and atrial fibrillation in children and in patients with congenital heart disease (CHD) is unknown.

METHODS

Data from 19 patients (age 6 months to 34 years, median 16 years) who received ibutilide for atrial flutter or atrial fibrillation between 1996 and 2005 was retrospectively reviewed. There were 15 patients with CHD (14 had prior heart surgery); four children had normal heart structure.

RESULTS

There were 74 episodes of atrial flutter and four episodes of atrial fibrillation (median episodes per patient was one, range 1-31). Ibutilide converted 55 of all the episodes (71%). Ibutilide was successful during its first-ever administration in 12 of 19 patients (63%). Fourteen episodes in six patients required electrical cardioversion after ibutilide failed. There were no episodes of symptomatic bradycardia. One patient went into torsade de pointes and one patient had nonsustained ventricular tachycardia.

CONCLUSION

With careful monitoring, ibutilide can be an effective tool in selected patients for cardioversion of atrial flutter.