Ventricular fibrillation cardioversion

Implantable cardioverter-defibrillator (ICD) A device implanted into the heart transvenously with a generator implanted subcutaneously in the pectoral area that provides internal electrical cardioversion of ventricular tachycardia or defibriUation of ventricular fibrillation. 

Lidocaine is the agent of choice for termination of ventricular tachycardia and prevention of ventricular fibrillation after cardioversion in the setting of acute ischemia. However, routine prophylactic use of lidocaine in this setting may actually increase total mortality, possibly by increasing the incidence of asystole, and is not the standard of care. Most physicians administer IV lidocaine only to patients with arrhythmias. 

Lidocaine Sodium channel (INa) blockade Blocks activated and inactivated channels with fast kinetics does not prolong and may shorten action potential Terminate ventricular tachycardias and prevent ventricular fibrillation after cardioversion IV first-pass hepatic metabolism reduce dose in patients with heart failure or liver disease Toxicity Neurologic symptoms... 

Digitalis-induced arrhythmias are frequently made worse by cardioversion this therapy should be reserved for ventricular fibrillation if the arrhythmia is glycoside-induced. 

Some of the beneficial effects of fish oils after acute myocardial infarction have been attributed to an antidysr-hythmic effect on the heart (5). However, the results of a randomized trial in 200 patients with implantable cardioverter defibrillators are at variance with this the rate of cardioversion was higher in those taking fish oils 1.8 g/day than in a control group who took olive oil (6). The lack of benefit and the suggestion that fish oil supplementation may increase the risk of ventricular tachycardia or ventricular fibrillation in some patients with implantable cardioverter defibrillators can reasonably be interpreted as evidence that the routine use of fish oil supplementation in patients with implantable cardioverter defibrillators and recurrent ventricular dysrhythmias should be avoided. 

Bretylium is usually used in an emergency setting, often during attempted resuscitation from ventricular fibrillation when lidocaine and cardioversion have failed. 

A 52-year-old woman with a wide-complex tachycardia was given adenosine 6,12, and another 12 mg as intravenous bolus doses immediately after the third dose she developed ventricular fibrillation (27). She recovered with cardioversion. 

Figure 8.31 (A) A patient with an acute myocardial infarction with evident ST-segment elevation and frequent, polymorphic, repetitive, PVC that triggers VF (asterisk) that was resolved with cardioversion. (B) Primary ventricular fibrillation in a patient with acute Ml. VF appears suddenly, without previous PVC and without evident ST-segment elevation. However, the underlying sinus rhythm is fast, which can often be present in cases of primary ventricular fibrillation and express the sympathetic overdrive that is usually present in acute phase of Ml (see p. 252). The electric cardioversion resolved the problem.

Patients with hemodynamically significant ventricular tachycardia or ventricular fibrillation not associated with an acute Ml who are resuscitated successfully (electrical cardioversion, pressors, amiodarone) are at high risk for death and should receive implantation of an internal cardioverter-defibrillator. 

Inappropriate use of IV verapamil Ventricular fibrillation Severe hypotension and/or myocardial ischemia Cardiac resuscitation (DC cardioversion) Misdiagnosis of VT as PSVT inappropriate use of verapamil... 

The introduction and manipulation of pacing leads are frequently associated with both tachyarrhythmias and bradyarrhythmias as a lead negotiates the chambers of the right heart. Ventricular tachycardia is extremely common as the pacing electrode or guidewire contacts the right ventricular myocardium. Simple withdrawal of these objects usually terminates the arrhythmia. In extreme cases, sustained monomorphic ventricular tachycardia and even ventricular fibrillation may occur. Some institutions have instituted a policy of placing external defibrillation pads prophylactically in anticipation of required cardioversion. 

Fig. 20.2 Detection and therapy parameters for an ICD. Top Detection parameters. As programmed the ICD defines ventricular tachycardia (VT) as 12 beats greater than 150 bpm and ventricular fibrillation (VF) as 12 of 16 beats greater than 188 bpm. An optional fast ventricular tachycardia (FVT) zone has not been programmed on. Bottom Therapies for ventricular fibrillation are a first shock at 24 J and subsequent shocks at 35 J. Therapies for ventricular tachycardia are two pacing sequences followed by cardioversion attempts at 15,35,35, and 35 J. Pacing for bradycardia is set at 40 bpm.

Fig. 20.6 The actual electrograms from the episode summary report in Fig. 17.5. The bipolar electrograms during ventricular fibrillation are relatively large but because of variability some of the electrograms were not sensed by the ICD (signal dropout). This underscores the importance of using a percentage of sensed ventricular depolarizations for detection of ventricular fibrillation. After delivery of energy, the ICD diagnoses success because of the slower rate of ventricular activity. CD, cardioversion/defibrillation CE, end of charge FD, fibrillation detect FS, fibrillation sense VS, normal sense.

FIGURE 6-2. Algorithm for the treatment of acute (top portion) paroxysmal supraventricular tachycardia and chronic prevention of recurrences (bottom portion). Note For empiric bridge therapy prior to radiofrequency ablation procedures, calcium channel blockers (or other atrioventricular [AV] nodal blockers) should not be used if the patient has AV reentry with an accessory pathway. (AAD, antiarrhythmic drugs AF, atrial fibrillation AP, accessory pathway AVN, atrioventricular nodal AVNRT, atrioventricular nodal reentrant tachycardia AVRT, atrioventricular reentrant tachycardia DCC, direct-current cardioversion ECG, electrocardiographic monitoring EPS, electrophysiologic studies PRN, as needed VT, ventricular tachycardia.)... 

Electrical cardioversion It may be desirable to reduce the dose of digoxin for 1 to 2 days prior to electrical cardioversion of atrial fibrillation to avoid the induction of ventricular arrhythmias, but physicians must consider the consequences of increasing the ventricular response if digoxin is withdrawn. If digitalis toxicity is suspected, delay elective cardioversion. If it is not prudent to delay cardioversion, select the lowest possible energy level to avoid provoking ventricular arrhythmias. Lab test abnormalities Periodically assess serum electrolytes and renal function (serum creatinine concentrations) the frequency of assessments will depend on the clinical setting. 

Kieny JR, Sacrez A, Facello A, et al. Increase in radionuclide left ventricular ejection fraction after cardioversion of chronic atrial fibrillation in idiopathic dilated cardiomyopathy. Eur. Heart J. 1992 13 1290-5. 

Supraventricular tachycardia is the major arrhythmia indication for verapamil. Adenosine or verapamil are preferred over older treatments (propranolol, digoxin, edrophonium, vasoconstrictor agents, and cardioversion) for termination. Verapamil can also reduce the ventricular rate in atrial fibrillation and flutter. It only rarely converts atrial flutter and fibrillation to sinus rhythm. Verapamil is occasionally useful in ventricular arrhythmias. However, intravenous verapamil in a patient with sustained ventricular tachycardia can cause hemodynamic collapse. 

Treatment of atrial fibrillation is initiated to relieve patient symptoms and prevent the complications of thromboembolism and tachycardia-induced heart failure, the result of prolonged uncontrolled heart rates. The initial treatment objective is control of the ventricular response. This is usually achieved by use of a calcium channel-blocking drug alone or in combination with a 13-adrenergic blocker. Digoxin may be of value in the presence of heart failure. A second objective is a restoration and maintenance of normal sinus rhythm. Several studies show that rate control (maintenance of ventricular rate in the range of 60-80 bpm) has a better benefit-to-risk outcome than rhythm control (conversion to normal sinus rhythm) in the long-term health of patients with atrial fibrillation. If rhythm control is deemed desirable, sinus rhythm is usually restored by DC cardioversion in the USA in... 

Therapeutic uses Quinidine is used in the treatment of a wide variety of arrhythmias, including atrial, AV junctional, and ventricular tachyarrhythmias. Quinidine is used to maintain sinus rhythm after direct current cardioversion of atrial flutter or fibrillation and to prevent frequent ventricular tachycardia. 

Arruodarone is used in chronic ventricular arrhythmias in atrial fibrillation it both slows the ventricular response and may restore sinus rhythm it may be used to maintain sinus rhythm after cardioversion for atrial fibrillation or flutter. Amiodarone should no longer be used for the management of reentrant supraventricular tachycardias associated with the Wolff-Parkinson-White syndrome as radiofrequency ablation is preferable. 

Atrial flutter, benefiting by the vagus nerve action of shortening the refractory period of the atrial muscle so that flutter is converted to fibrillation (in which state the ventricular rate is more readily controlled). Electrical cardioversion is preferred. 

An 86-year-old woman was given adenosine 12 mg intravenously for sustained supraventricular tachycardia, which terminated but was followed by atrial fibrillation and paroxysmal ventricular tachycardia (24). Cardioversion was unsuccessful, but normal sinus rhythm was obtained with procainamide. This followed an anteroseptal myocardial infarction. 

In a comparison of intravenous dofetihde (8 micrograms/kg n = 48), amiodarone (5mg/kg n=50), or placebo (n = 52) in converting atrial fibrillation or flutter to sinus rhythm in 150 patients, two patients given dofetilide had non-sustained ventricular tachycardias four had torsade de pointes, in one case requiring electrical cardioversion (53). 

In 24 patients with atrial fibrillation who underwent elective transvenous cardioversion for atrial fibrillation, flecainide reduced the energy requirements for further defibrillation after induction of atrial fibrillation by atrial pacing (27). There were no ventricular dysrhythmias, but transient bradycardia requiring ventricular pacing occurred in two patients. Two patients had transient asymptomatic hjrpotension after flecainide and one reported transient dizziness and some hght-headedness. 

The use of propafenone in atrial fibrillation (SEDA-23, 202) has been studied in a randomized, double-bhnd, placebo-controUed trial in 55 patients (17). The dose of propafenone was chosen according to body weight 450, 600, and 750 mg for those weighing 50-64, 65-80, and over 80 kg respectively. Propafenone converted atrial fibrillation to sinus rhythm significantly more quickly than placebo, and most patients given propafenone had converted by 6 hours. However, by 24 hours there was no significant difference between the two groups. Four patients had hypotension after propafenone, in three cases transiently. The patient with sustained hypotension had poor left ventricular systolic function, but it responded promptly to the administration of fluids and electrical cardioversion. In one patient with transient hypotension there was a brief episode of sinus bradycardia and in another an isolated sinus pause. 

A 65-year-old woman, who had had normal preoperative serum electrolytes and a normal QT interval with sinus rhythm, received hydroxyzine and atropine premedication followed by thiopental and vecuronium for anesthetic induction. Endotracheal intubation was difficult and precipitated atrial fibrillation, which was refractory to disopyramide 100 mg. Anesthesia was then maintained with sevoflurane 2% and nitrous oxide 50%. Ten minutes later ventricular tachycardia ensued, refractory to intravenous lidocaine, disopyramide, and magnesium. DC cardioversion resulted in a change to a supraventricular tachycardia, which then deteriorated to torsade de pointes. External cardiac massage and further DC cardioversion were initially unsuccessful, but the cardiac rhythm reverted to atrial fibrillation 10 minutes after the sevoflurane was switched off. Two weeks later she had her operation under combined epidural and general anesthesia, with no changes in cardiac rhythm. 

C Diltiazem. Quinidine can be used to maintain normal sinus rhythm (NSR) after cardioversion of atrial fibrillation. Metoprolol is commonly used to control ventricular rate before conversion to NSR. However, this patient has two contraindications (COPD and diabetes) for beta-blocker use. Unlike diltiazem, amlodipine and nimodipine do not block AV nodal conduction therefore, they would be ineffective at rate control. 

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