Page 418 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

288 PART 3: Cardiovascular Disorders

cardioversion, for example, 50 J, whereas higher energies may be Catheter ablation for cure of atrial flutter is an effective therapy.
54
required for atrial fibrillation (≥120 J for biphasic). Since the incor- Atrial fibrillation ablation/pulmonary vein isolation can be considered
poration of biphasic waveforms into external defibrillators, it is rare for long-term cure of AF in selected patients. AV junction ablation and
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for cardioversion to fail to convert recent onset AF. Atrial flutter may ventricular pacing is an effective option in patients in whom effective
be terminated by rapid atrial overdrive pacing. Some dual chamber ventricular rate control of AF cannot be achieved pharmacologically
pacemakers and implantable defibrillators have atrial antitachycardia (please note these patients still require anticoagulation since their atria
pacing therapies for pace termination of atrial flutter. are still in fibrillation). 44,54
If AF/flutter has persisted for ≥48 hours in the absence of effective The patient with AF or atrial flutter is at risk of thromboembolism
anticoagulation, therapy should be aimed at achieving ventricular rate particularly if the patient is older or has structural heart disease. The
40
control (HR <100 bpm). 44,45 Pharmacologic cardioversion to sinus rhythm CHADS score is frequently used for assessment of risk of stroke or
2
can be considered if the patient has been in AF <48 hours. Anticoagulant systemic thromboembolism (Table 36-8). Aspirin is indicated for pre-
46
46
therapy with heparin or low molecular weight heparin should be initi- vention of thromboembolism in very low-risk patients whereas antico-
ated. If cardioversion is performed, anticoagulant therapy should be agulation with heparin and then warfarin is required in high-risk patients
continued for at least 4 weeks following cardioversion. 16,40,46 Ibutilide or (Table 36-8). 40,56 New anticoagulants are emerging, such as dabigatran that
procainamide can be administered intravenously to promote pharmaco- may be more effective than warfarin. Dabigatran does not require frequent
logic conversion for recent onset AF/flutter or in patients who have been laboratory monitoring. Dabigatran has been shown to reduce the risk of
57
on effective long term anticoagulation (Table 36-8). The ECG must be stroke compared to warfarin and to reduce the risk of major hemorrhagic
16
monitored for significant Q ˙ t interval prolongation as both these drugs complications. If the patient has not been on anticoagulant therapy,
57
may cause torsade de pointes V . Intravenous magnesium (1-2 g IV) electrical or pharmacologic cardioversion should be deferred for at least
7
t
administered prior to administration of ibutilide may prevent torsade 3 weeks if the patient has been in AF/flutter for ≥48 hours or if the dura-
de pointes V . Intravenous amiodarone is less effective in promoting tion is unknown. Alternatively, a transesophageal echocardiogram can be
44
46
t
acute conversion to sinus rhythm although it may facilitate improved rate performed to demonstrate the absence of intracardiac thrombus if restora-
control. One important principle in the management of AF is that most tion of sinus rhythm is desired urgently. Patients should be maintained on
47
patients deserve at least one attempt at restoration of sinus rhythm. 40 oral anticoagulation for at least 4 weeks following electrical cardioversion.
The decision to initiate Class I or III antiarrhythmic drug therapy to
maintain sinus rhythm should be based the patient’s symptoms and/
or the hemodynamic significance of the arrhythmia. In the relatively Super Ventricular Tachycardia
44
asymptomatic patient, rate control is a reasonable first approach. 48,49
β-Blockers, verapamil, or diltiazem should be prescribed in doses to
achieve a ventricular rate at rest or with minimal activity <100 bpm
(Table 36-4). 16,44,45 Digoxin alone is frequently ineffective in achieving rate
control of AF or atrial flutter although it may be synergistic with Class II or
IV antiarrhythmic drugs. Rhythm control with Class I or III antiarrhyth-
mic drugs may be desirable in the very symptomatic patient or when these Hemodynamically Hemodynamically
arrhythmias cause adverse hemodynamic effects. 48-51 AV node blocking Unstable Stable
drugs are required in conjunction with Class I/III antiarrhythmic drugs
as AF/flutter is usually paroxysmal in nature and these drugs are rarely
100% effective at suppression. The dosages, potential side effects and drug 12 Lead
interactions of these drugs are summarized in Table 36-4. Class I drugs are Synchronized ECG b
contraindicated for chronic prophylaxis in patients with a prior myocardial Cardioversion
a
infarction. Class I drugs and sotalol are relatively contraindicated in those 120–200 J
with significant left ventricular dysfunction because of the risk of ventricu-
lar proarrhythmia. 7,11,40,52,53 Long-term antiarrhythmic drug therapy for Vagal
prevention of AF/flutter may not be required if the episode is thought to Maneuvers
be due to a reversible cause, for example, pneumonia or perioperative state.
TABLE 36-8 Antithrombotic Treatment for Paroxysmal and Chronic Atrial Adenosine
Fibrillation—Based on Risk Stratification—CHADS
2 6–24 mg IV
Risk Factors Score
(C) Congestive heart failure 1
LVEF 35% or less Metoprolol
(H) Hypertension 1 5 mg IV over 1–2 min
Can repeat × 3
(A) Age >75 years 1 or
(D) Diabetes mellitus 1 Verapamil
5 mg IV Over
(S) Previous stroke or embolism 2 1–2 min
Maximum score 6 Can repeat × 3
Total score <0 Aspirin 81-325 mg daily
FIGURE 36-7. Management algorithm for SVT (supraventricular tachycardia).
Total score = 1 Aspirin or oral Anticoagulant b
a 200 J for monophasic.
Total score >1 a Oral anticoagulant b
b In addition to the 12-lead ECG, monitoring strips obtained during conversion can also be helpful in
a Mitral stenosis and prosthetic heart valves are also high risk factors. establishing a diagnosis. Please note that significant hemodynamic instability with tachycardias less
b Warfarin or dabigatran. INR (International Ratio) targets for warfarin are usually 2 to 3 and may be than 150 bpm are uncommon except with LV dysfunction and may be suggestive of an alternative cause
higher in the context of prosthetic valves. of the hemodynamic compromise other than the tachycardia.

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