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ATRIAL FIBRILLATION (AF)/FLUTTER
Chest palpitations, light-headedness, and reduced exercise tolerance are
the most common symptoms of AF, but stroke is among the severe
complications. The goals of therapy are to control the ventricular rate
and reduce the risk of stroke.
Digoxin, β-blockers, and nondihydropyridine calcium-channel blockers
are appropriate rate-controlling medications. Digoxin is usually
adjunctive therapy. Antiarrhythmic drugs are recommended in patients
with symptoms but not needed in asymptomatic patients (no symptoms
Before converting AF to sinus rhythm, assurance of a lack of clot is
important but not required if someone is unconscious or
hemodynamically unstable. People with a CHA2DS2
or greater should receive chronic anticoagulant therapy with warfarin,
dabigatran, rivaroxaban, edoxaban, or apixaban. Those with a score of 0
do not require antithrombotic therapy, and those with a score of 1 can
receive no therapy, aspirin, or anticoagulant therapy based on patient
Antiarrhythmic drugs convert patients out of AF 50% of the time,
whereas electricalshock is successful 90% of the time. To maintain
sinus rhythm after conversion, class Ib agents cannot be used, class Ic
agents cannot be used in patients with structural heart disease (left
ventricular hypertrophy, myocardial infarction, or heart failure), and
class Ia and III agents can increase the risk of torsades de pointes.
Propafenone, sotalol, dronedarone, dofetilide, and amiodarone are
commonly used antiarrhythmic agents for AF.
Atrial flutter is less common than AF, but similar rate control and
antiarrhythmic strategies can be tried. Radiofrequency ablation can be
used to terminate atrial flutter.
PAROXYSMAL SUPRAVENTRICULAR TACHYCARDIA (PSVT)
PSVT is caused by reentry within the atrioventricular (AV) node.
Palpitations and hypotension can occur. The Valsalva maneuver,
adenosine, or nondihydropyridine calcium-channel blockers can be used
In Wolff–Parkinson–White syndrome patients with PSVT, the use of
AV nodal blocking agents such as β-blockers, nondihydropyridine
calcium-channel blockers, and digoxin can increase the risk of cardiac
arrest. Ablation can destroy the bypass tract and cure the patient.
β-Blockers, digoxin, and nondihydropyridine calcium-channel blockers
should be withheld in patients with type 1 second- or third-degree AV
block. Atropine can be used to treat this disorder.
In patients with premature ventricular complexes (PVCs) and
β-blockers are the treatment of choice. Catheter ablation is
recommended for those with ventricular compromise due to high PVC
Patients with myocardial infarction and nonsustained ventricular
tachycardia (VT) should receive β-blockers and need to be evaluated to
determine whether they should receive an implantable cardioverterdefibrillator (ICD).
Patients with sustained VT should be treated with intravenous
antiarrhythmic agents unless they are hemodynamically unstable, in
which case they should be electrically converted. To prevent death from
arrhythmia recurrence, ICDs are superior to antiarrhythmic drugs, but to
decrease the occurrence of painfulshocks, both strategies may be used
TdP occurs secondary to antiarrhythmic and nonantiarrhythmic
medications that prolong the QTc interval. Class Ia and III
antiarrhythmic agents, antipsychotic agents, citalopram,
fluoroquinolones, macrolides, azole antifungals, and methadone can
prolong the QTc interval. Magnesium is the treatment of choice for
hemodynamically stable TdP with electrical cardioversion reserved for
Cardiac arrest should be treated with 2-minute cycles of aggressive
cardiopulmonary resuscitation, electricalshock for VT or ventricular
fibrillation (VF), epinephrine or vasopressin, and amiodarone for
refractory VT or VF according to the Advanced Cardiac Life Support
guidelines from the American Heart Association.
Adequate circulation depends on continuous, well-coordinated electrical activity
within the heart. This chapter reviews and discusses cardiac electrophysiology,
arrhythmogenesis, common arrhythmias, and antiarrhythmic treatment.
Understanding Electrophysiology
An electrical potential exists across the cell membrane, and the electrical potential
changes in a cyclic manner that is related to the flux of K+
If the change in the membrane potential is plotted against time in
a given cycle of a His-Purkinje fiber, a typical action potential results (Fig. 15-1).
The action potential can be described in five phases.
ventricular depolarization resulting from sodium entry into the cell through fast
sodium channels. On a surface electrocardiogram (ECG), phase 0 is represented by
the QRS complex. Phase 1 is the overshoot phase in which calcium enters the cell
and contraction occurs. During phase 2, the plateau phase, inward depolarizing
currents through slow sodium and calcium channels are counterbalanced by outward
repolarizing potassium currents. Phase 3 constitutes repolarization, which on the
ECG is represented by the T wave. During phase 4, sodium moves out of the cell and
potassium moves into the cell via an active pumping mechanism. During this phase,
the action potential remains flat in some cells (e.g., ventricular muscle) and does not
change until it receives an impulse from above. In other cells (e.g., sinoatrial [SA]
node), the cell slowly depolarizes until it reaches the threshold potential and again
spontaneously depolarizes (phase 0). The shape of the action potential depends on
the location of the cell (see Fig. 15-1). In both the SA and atrioventricular (AV)
nodes, the cells are more dependent on calcium influx than sodium influx, resulting in
a less negative resting membrane potential, a slow rise of phase 0, and the capability
of spontaneous (automatic) phase 4 depolarization (Fig. 15-1).
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