Advanced cardiac life support antiarrhythmic drugs

[Life-threatening brady- and tachyarrhythmias]

Bradycardic (heart rate<50/min) and tachycardic heart rhythm disturbances (100/min) require rapid therapeutic strategies. Supraventricular tachycardias (SVT) are sinus tachycardia, atrial tachycardia, AV-nodal reentrant tachycardia and tachycardia due to accessory pathways. Mostly SVT are characterized by small QRS complexes (QRS width<0.12 ms). It is essential to evaluate the arrhythmia history, to perform a good physical examination and to exactly analyze the 12-lead electrocardiogram. An exact diagnosis is then possible in >90% of SVT patients. Ventricular tachycardias have a broad QRS complex (>or=0.12 s), ventricular flutter and ventricular fibrillation are associated with chaotic electrophysiologic findings. For acute therapy, we will present the new concept of the "5A" that includes adenosine, adrenaline, ajmaline, amiodarone and atropine. Additional "B, C and D strategies" include betablocking agents, cardioversion as well as defibrillation. The "5A" concept allows a safe and effective antiarrhythmic treatment of all bradycardic and tachycardic arrhythmias as well as asystolia.

Procainamide and survival in ventricular fibrillation out-of-hospital cardiac arrest

OBJECTIVES

Procainamide is an antiarrhythmic drug of unproven efficacy in cardiac arrest. The association between procainamide and survival from out-of-hospital cardiac arrest was investigated to better determine the drug's potential role in resuscitation.

METHODS

The authors conducted a 10-year study of all witnessed, out-of-hospital, ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT) cardiac arrests treated by emergency medical services (EMS) in King County, Washington. Patients were considered eligible for procainamide if they received more than three defibrillation shocks and intravenous (IV) bolus lidocaine. Four logistic regression models were used to calculate odds ratios (ORs) and 95% confidence intervals (CI) describing the relationship between procainamide and survival.

RESULTS

Of the 665 eligible patients, 176 received procainamide, and 489 did not. On average, procainamide recipients received more shocks and pharmacologic interventions and had lengthier resuscitations. Adjusted for their clinical and resuscitation characteristics, procainamide recipients had a lower likelihood of survival to hospital discharge (OR = 0.52; 95% CI = 0.36 to 0.75). Further adjustment for receipt of other cardiac medications during resuscitation negated this apparent adverse association (OR = 1.02; 95% CI = 0.66 to 1.57).

CONCLUSIONS

In this observational study of out-of-hospital VF and pulseless VT arrest, procainamide as second-line antiarrhythmic treatment was not associated with survival in models attempting to best account for confounding. The results suggest that procainamide, as administered in this investigation, does not have a large impact on outcome, but cannot eliminate the possibility of a smaller, clinically relevant effect on survival.

Treating critical supraventricular and ventricular arrhythmias

Atrial fibrillation (AF), atrial flutter, AV-nodal reentry tachycardia with rapid ventricular response, atrial ectopic tachycardia and preexcitation syndromes combined with AF or ventricular tachyarrhythmias (VTA) are typical arrhythmias in intensive care patients (pts). Most frequently, the diagnosis of the underlying arrhythmia is possible from the physical examination (PE), the response to maneuvers or drugs and the 12-lead surface electrocardiogram. In unstable hemodynamics, immediate DC-cardioversion is indicated. Conversion of AF to sinus rhythm (SR) is possible using antiarrhythmic drugs. Amiodarone has a conversion rate in AF of up to 80%. Ibutilide represents a class III antiarrhythmic agent that has been reported to have conversion rates of 50-70%. Acute therapy of atrial flutter (Aflut) in intensive care pts depends on the clinical presentation. Atrial flutter can most often be successfully cardioverted to SR with DC-energies <50 joules. Ibutilide trials showed efficacy rates of 38-76% for conversion of Aflut to SR compared to conversion rates of 5-13% when intravenous flecainide, propafenone or verapamil was administered. In addition, high dose (2 mg) of ibutilide was more effective than sotalol (1.5 mg/kg) in conversion of Aflut to SR (70 versus 19%). Drugs like procainamide, sotalol, amiodarone or magnesium were recommended for treatment of VTA in intensive care pts. However, only amiodarone is today the drug of choice in VTA pts and also highly effective even in pts with defibrillation-resistant out-of-hospital cardiac arrest (CA). There is a general agreement that bystander first aid, defibrillation and advanced life support is essential for neurologic outcome in pts after cardiac arrest due to VTA. Public access defibrillation in the hands of trained laypersons seems to be an ideal approach in the treatment of ventricular fibrillation (VF). The use of automatic external defibrillators (AEDs) by basic life support ambulance providers or first responder (FR) in early defibrillation programs has been associated with a significant increase in survival rates (SRs). However, use of AEDs at home cannot be recommended.

Concept of the five 'A's for treating emergency arrhythmias

Cardiac rhythm disturbances such as bradycardia (heart rate < 50/min) and tachycardia (heart rate > 100/min) require rapid therapeutic intervention. The supraventricular tachycardias (SVTs) are sinus tachycardia, atrial tachycardia, AV-nodal reentrant tachycardia, and tachycardia due to accessory pathways. All SVTs are characterized by a ventricular heart rate > 100/min and small QRS complexes (QRS width < 0.12 ms) during the tachycardia. It is essential to evaluate the arrhythmia history, to perform a good physical examination, and to accurately analyze the 12-lead electrocardiogram. A precise diagnosis of the SVT is then possible in more than 90% of patients. In ventricular tachycardia (VT) there are broad QRS complexes (QRS width > 0.12 s). Ventricular flutter and ventricular fibrillation are associated with chaotic electrophysiologic findings. For acute therapy, we will present the new concept of the five 'A's, which refers to adenosine, adrenaline, ajmaline, amiodarone, and atropine. Additionally, there are the 'B,' 'C,' and 'D' strategies, which refer to beta-blockers, cardioversion, and defibrillation, respectively. The five 'A' concept allows a safe and effective antiarrhythmic treatment of all bradycardias, tachycardias, SVTs, VT, ventricular flutter, and ventricular fibrillation, as well as of asystole.

Magnesium deficiency in critical illness

Magnesium (Mg) deficiency commonly occurs in critical illness and correlates with a higher mortality and worse clinical outcome in the intensive care unit (ICU). Magnesium has been directly implicated in hypokalemia, hypocalcemia, tetany, and dysrhythmia. Moreover, Mg may play a role in acute coronary syndromes, acute cerebral ischemia, and asthma. Magnesium regulates hundreds of enzyme systems. By regulating enzymes controlling intracellular calcium, Mg affects smooth muscle vasoconstriction, important to the underlying pathophysiology of several critical illnesses. The principle causes of Mg deficiency are gastrointestinal and renal losses; however, the diagnosis is difficult to make because of the limitations of serum Mg levels, the most common assessment of Mg status. Magnesium tolerance testing and ionized Mg2+ are alternative laboratory assessments; however, each has its own difficulties in the ICU setting. The use of Mg therapy is supported by clinical trials in the treatment of symptomatic hypomagnesemia and preeclampsia and is recommended for torsade de pointes. Magnesium therapy is not supported in the treatment of acute myocardial infarction and is presently undergoing evaluation for the treatment of severe asthma exacerbation, for the prevention of post-coronary bypass grafting dysrhythmias, and as a neuroprotective agent in acute cerebral ischemia.

Advances in the acute pharmacologic management of cardiac arrhythmias

Safe and effective control of rapid ventricular rates in acute-onset atrial fibrillation (AF) can be accomplished with intravenous calcium antagonists, beta-blockers or amiodarone; digoxin is less effective. If pharmacologic cardioversion of AF is desired, single oral doses of propafenone or flecainide are safe and effective in patients without structural heart disease. Intravenous ibulitide is moderately effective in the conversion of persistent AF or atrial flutter, with a small risk of proarrhythmia. In wide QRS complex tachycardia of uncertain origin, adenosine and lidocaine are no longer recommended. Procainamide or amiodarone are the treatment options, but attempts should be made to define the origin of tachycardia. In the treatment of monomorphic ventricular tachycardia, lidocaine is no longer recommended; procainamide or amiodarone are the recommended therapies. In polymorphic ventricular tachycardia with a normal QT interval, beta-blockers are recommended. In shock-refractory ventricular fibrillation, lidocaine, and magnesium are ineffective; intravenous amiodarone should be the treatment of choice.

Strategies for reversing shock-resistant ventricular fibrillation

PURPOSE OF REVIEW

Shock-resistant ventricular fibrillation is defined as ventricular fibrillation persisting after three defibrillation attempts. In approximately 10 to 25% of all cardiac arrests, shock-resistant ventricular fibrillation develops, and 87 to 98% of these patients die.

RECENT FINDINGS

In the treatment of shock-resistant ventricular fibrillation, defibrillation using biphasic waveforms is considered as an intervention of choice. Intravenous amiodarone is also acceptable, safe, and useful, based on evidence from two randomized clinical trials. Intravenous vasopressin is acceptable and probably safe and useful, but the evidence supporting this recommendation is coming from a small, randomized clinical trial. Procainamide is acceptable but not recommended. In the presence of acute myocardial infarction and recurrent ventricular fibrillation, if all other therapies fail, beta-blockers can be considered. Magnesium, lidocaine, and bretylium are not recommended in the treatment of shock-resistant ventricular fibrillation.

SUMMARY

Biphasic defibrillation and intravenous amiodarone are useful in shock-resistant ventricular fibrillation.