Oral class III antiarrhythmics: what is new?

Compliance with the north American Society of Pacing and Electrophysiology guidelines on amiodarone monitoring in Riyadh, Saudi Arabia: a retrospective charts review study

Background

Amiodarone is known for its efficacy as an antiarrhythmic agent; however, its extensive side-effect profile requires careful selection of patients and frequent monitoring. The purpose of this study was to evaluate the performance of the baseline tests before initiating amiodarone therapy and the on-going monitoring based on the North American Society of Pacing and Electrophysiology guidelines recommendations.

Methods

A retrospective descriptive charts review study included all patients who are 18 years of age and older and were started on oral amiodarone with a primary diagnosis of any type of cardiac arrhythmia from January 2016 to December 2018 in King Abdualziz Medical City, Riyadh, Saudi Arabia. The medical charts were reviewed and evaluated based on the performance of the recommended baseline and follow-up of chest X-ray (CXR), liver function test (LFT), thyroid function test (TFT) and electrocardiogram (ECG). The continuous variables were analyzed and presented as mean ± SD and the categorical variables were presented as percentages.

Results

Over the study period, 143 eligible participants on amiodarone therapy were included, with an average of 165 ± 207 days on amiodarone. Of patients, 36.4% had the entire recommended baseline assessments before initiating amiodarone. Our results indicated optimal compliance rates to the baseline tests of CXR (79.7%), LFT (79.7%) and ECG (86.7%). However, there was a lower compliance rate to TFT recommendations (40.6%). The compliance rate to the guideline recommendations related to the follow-up tests was minimal. On-going monitoring performance rates were 47.6% of CXR, 49% of LFT, 54.5% of ECG and 22.4% of TFT.

Conclusion

The compliance with the guideline recommendations related to amiodarone baseline assessments was optimal for all the baseline tests, except for TFT. However, the proportion of patients who received all the recommended baseline assessments was minimal. In addition, the performance of on-going monitoring was suboptimal for all the follow-up tests. Improvements could be made by establishing a local protocol for amiodarone monitoring and pharmacists participating in amiodarone therapy assessments.

The eye in CHD

In recent years, there has been a rise in the number patients with CHD surviving into adulthood. Many have complications related to their CHD or its treatments, outside the heart, including ocular abnormalities. The objective of this review is to highlight the ocular abnormalities that occur in adults with CHD, either from their condition or related to the common drugs prescribed to manage it. In particular, we reviewed the effects of cyanosis, coarctation of the aorta, endocarditis, and the side effects of Sildenafil and Amiodarone. A change in the retinal vasculature is a common observation with cyanosis or coarctation of the aorta. Occlusion of the retinal vessels may also be observed in cyanotic patients, as well as those with infectious endocarditis. Sildenafil has established ocular side effects; here they are explored in the context of therapy for pulmonary hypertension. Similarly, Amiodarone has established ocular risks, which are summarised. The high prevalence of ocular consequences in adult CHD patients reinforces the need for knowledge of the risks involved and for frequent ophthalmological screening where appropriate.

Current treatment options for atrial flutter and results with cryocatheter ablation

Rhythm disturbances arising in the upper chambers of the heart are not uncommon. They are associated with a heavy burden of illness for the affected individual, as well as society in general. Atrial flutter, a re-entrant atrial tachycardia, is one such rhythm disturbance. The objective of this review article is twofold: first, to provide a brief insight into atrial flutter and the typical treatments for this arrhythmia in clinical practice; and second, to give an in-depth account of cryocatheter ablation as a relatively new treatment option for this potentially debilitating condition. The many recent clinical studies documenting the use of cryocatheter ablation for treatment of atrial flutter are presented, and their results briefly discussed. Overall, as cryocatheter ablation embeds itself among the arsenal of treatments for atrial flutter, the promising results from clinical studies appear destined to elevate cryocatheter ablation to a premier position among the treatment options for atrial flutter.

Amiodarone supplants lidocaine in ACLS and CPR protocols

Amiodarone is an antiarrhythmic medication used to treat and prevent certain types of serious, life-threatening ventricular arrhythmias. Amiodarone gained slow acceptance outside the specialized field of cardiac antiarrhythmic surgery because the side-effects are significant. Recent adoption of amiodarone in the ACLS (Advanced Cardiac Life Support) protocol has somewhat popularized this class of antiarrhythmics. Its use is slowly expanding in the acute medicine setting of anesthetics. This article summarizes the use of Amiodarone by anesthesiologists in the operating room and during cardiopulmonary resuscitation.

The Electro-Mechanical window: a risk marker for Torsade de Pointes in a canine model of drug induced arrhythmias

BACKGROUND AND PURPOSE

In cardiovascular pharmacology, electrical and mechanical events can be distinguished, and the phrase 'electro-mechanical window' (EMw) describes the temporal difference between these events. We studied whether changes in EMw have potential predictive value for the occurrence of arrhythmias in fentanyl/etomidate-anaesthetized beagle (FEAB) dogs.

EXPERIMENTAL APPROACH

The EMw was calculated as differences between the QT interval and QLVP(end) in FEAB dogs during atrial pacing, treatment with isoprenaline or atropine, body temperature changes and induction of Torsade de Pointes (TdP) in an LQT1 model.

KEY RESULTS

The electrical systole (QT interval) was shorter than the duration of the mechanical event (QLVP(end) ), providing a positive EMw. Atrial pacing, atropine or body temperature changes had no major effects on EMw, despite large changes in QT duration. However, β-adrenoceptor stimulation (with isoprenaline) decreased the EMw (from 90 to 5 ms) and in combination with HMR1556, a blocker of the slowly activating potassium current (I(Ks) ), induced a large negative EMw (-109ms) and TdP. Prevention of TdP by atenolol or verapamil was associated with a less negative EMw (-23 to -16ms). Mexiletine, a poorly effective long QT treatment, did not affect the EMw or prevent TdP induction.

CONCLUSIONS AND IMPLICATIONS

The EMw is a marker, other than QT prolongation, of TdP risk in the FEAB model. Therefore, we suggest examining the EMw as a risk marker in cardiovascular safety studies and as a potential biomarker to improve clinical management of long QT syndrome patients, especially in patients with borderline QT prolongation.

Recurrent syncope associated with paroxysmal supraventricular tachycardia in a Devon Rex cat diagnosed by implantable loop recorder

A 9-year-old male neutered Devon Rex cat was presented for continued investigations following a 7-year history of recurrent syncope. Previous diagnostic tests, including 24h (Holter) electrocardiographic monitoring, had failed to identify the aetiology of such episodes, and former empirical treatment with atenolol had not provided satisfactory control of the clinical signs. A conclusive diagnosis was eventually achieved using an implantable loop recorder (Reveal), which identified paroxysmal supraventricular tachycardia (SVT) associated with a syncopal episode. Treatment with oral sotalol was instituted and, 18 months after initiation of anti-arrhythmic therapy, no further syncopal episodes have been observed by the cat's owners.

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.

Comparative antiarrhythmic efficacy of amiodarone and dronedarone during acute myocardial infarction in rats

The effects of dronedarone, a non-iodinated derivative of amiodarone, on ventricular tachycardia and ventricular fibrillation post-myocardial infarction are not well established. Fifty-five Wistar rats were randomly allocated to a 2-week oral treatment with either vehicle (n=18), amiodarone (30 mg/kg, n=20), or dronedarone (30 mg/kg, n=17). After acute coronary artery ligation, a single-lead electrocardiogram was continuously recorded for 24 h and episodes of ventricular tachycardia/fibrillation as well as mortality rates were analysed. Monophasic action potential recordings were obtained from the left ventricular epicardium at baseline and 24 h post-myocardial infarction. Thyroid hormones and catecholamines were measured using radioimmunoassay. Thyroid function was similar in the 3 groups. Compared to controls, amiodarone and dronedarone equally decreased the number of ventricular tachycardia/fibrillation episodes by approximately 75%. Both agents prevented the increase in monophasic action potential duration and in beat-to-beat variation. Norepinephrine levels were lower only after amiodarone treatment. Despite the observed antiarrhythmic effect, total mortality did not differ between groups (38.8% in controls, 30.0% in the amiodarone group and 58.8% in the dronedarone group), because of excess bradyarrhythmic mortality in both drug groups that reached significance in the dronedarone group. Dronedarone and amiodarone display similar antiarrhythmic efficacy post-myocardial infarction, partly by preventing repolarization inhomogeneity. However, dronedarone increases bradyarrhythmic mortality possibly secondary to its negative inotropic effects.

The role of late I and antiarrhythmic drugs in EAD formation and termination in Purkinje fibers

Multiple components of cardiac Na current play a role in determining electrical excitation in the heart. Recently, the role of nonequilibrium components in controlling cardiac action potential plateau duration, and their importance in regulating the occurrence of afterdepolarizations and arrhythmias have garnered more attention. In particular, late Na current (late I(Na)) has been shown to be important in LQT2 and LQT3 arrhythmias. Class III agents like dofetilide, clofilium, and sotalol, which can all cause a drug-induced form of LQT2, significantly lengthen action potential duration at 50% and 90% repolarization in isolated rabbit Purkinje fibers, and can initiate the formation of early afterdepolarizations, and extra beats. These actions can lead to the development of a serious ventricular tachycardia, torsades de pointes, in animal models and patients. However, pretreatment with agents that block late I(Na), like lidocaine, mexiletine, and RSD1235, a novel mixed ion channel blocker for the rapid pharmacologic conversion of atrial fibrillation, significantly attenuates the prolonging effects of Class III agents or those induced by ATX-II, a specific toxin that delays Na channel inactivation and amplifies late I(Na) greatly, mimicking LQT3. The Na channel block caused by lidocaine and RSD1235 can be through the open or inactivated states of the channel, but both equivalently inhibit a late component of Na current (I(Na)), recorded at 22 degrees C using whole-cell patch clamp of Nav 1.5 expressed in HEK cells. These protective actions of lidocaine, mexiletine, and RSD1235 may result, at least in part, from their ability to inhibit late I(Na) during action potential repolarization, and inhibition of the inward currents contributing to EAD and arrhythmia formation.

Monitoring the use of amiodarone: compliance with guidelines

AIM

Careful monitoring of amiodarone is recommended because it produces a range of potentially severe adverse effects. The aim of this study was to compare existing practice at our hospitals with the current international guidelines for the use of this drug.

METHODS

A retrospective audit was carried out on all patients aged 15 years or older, with a primary discharge diagnosis of tachyarrhythmia and who were commenced and discharged alive on amiodarone between 1 January 2000 and 30 June 2002 from Wellington and Kenepuru Hospitals, Capital and Coast District Health Board, Wellington, New Zealand. The medical records were examined for baseline measurements of renal, liver, thyroid and pulmonary function, the electrocardiogram and chest X-ray. Follow-up arrangements were sought postdischarge. A questionnaire was sent to the general practitioner requesting information on follow-up testing.

RESULTS

During the trial period, 743 patients were admitted with a primary diagnosis of tachyarrhythmia. Eighty-six patients satisfied the entry criteria, and of these 58 were followed for at least 1 year postdischarge. Baseline testing of the electrocardiogram, full blood count and renal function testing was excellent (95-100%). Chest X-rays were carried out in 80% of patients. Baseline testing of thyroid (61%) and liver (44%) function was suboptimal. Two percent of patients had pulmonary function testing and no patient had a formal eye examination. At 6 months, only 32% had thyroid function tests and 41% had liver function tests. At 1 year, of those still on treatment, 35% had both liver and thyroid function tests.

CONCLUSION

Monitoring of thyroid, liver and pulmonary function tests in patients on amiodarone is less than ideal. This is probably because of lack of awareness of current guidelines.

The Mechanism of Atrial Antiarrhythmic Action of RSD1235

INTRODUCTION

RSD1235 is a novel drug recently shown to convert AF rapidly and safely in patients.(1) Its mechanism of action has been investigated in a rat model of ischemic arrhythmia, along with changes in action potential (AP) morphology in isolated rat ventricular myocytes and effects on cloned channels.

METHODS AND RESULTS

Ischemic arrhythmias were inhibited with an ED50 of 1.5 micromol/kg/min, and repolarization times increased with non-significant effects on PR and QRS durations. AP prolongation was observed in rat myocytes at low doses, with plateau elevation and a reduction in the AP overshoot at higher doses. RSD1235 showed selectivity for voltage-gated K+ channels with IC50 values of 13 microM on hKv1.5 (1 Hz) versus 38 and 30 microM on Kv4.2 and Kv4.3, respectively, and 21 microM on hERG channels. RSD1235 did not block IK1 (IC50 > 1 mM) nor ICa,L (IC50= 220 microM) at 1 Hz in guinea pig ventricular myocytes (n = 4-5). The drug displayed mild (IC50= 43 microM at 1 Hz) open-channel blockade of Nav1.5 with rapid recovery kinetics after rate reduction (10-->1 Hz, 75% recovery with tau= 320 msec). Nav1.5 blocking potency increased with stimulus frequency from an IC50= 40 microM at 0.25 Hz, to an IC50= 9 microM at 20 Hz, and with depolarization increasing from 107 microM at -120 mV to 31 microM at -60 mV (1 Hz).

CONCLUSIONS

These data suggest that RSD1235's clinical selectivity and AF conversion efficacy result from block of potassium channels combined with frequency- and voltage-dependent block of INa.