Most Effective Pad Placement in Elective Cardioversion

Q: In the unit where I work, we do many elective cardioversions. What is the most effective placement of the pads on the anterior and posterior chest?A: Kayla Little, MSN, APRN, AGCNS-BC, PCCN, CHFN, and Deborah Klein, MSN, APRN, ACNS-BC, CCRN, reply:Atrial fibrillation, the most common clinical arrhythmia, is characterized by irregular electrical impulses that result in ineffective atrial contractions.1-4 Rapid focal firing most often occurs in the pulmonary veins, initiating atrial fibrillation.1 The sinoatrial node, located in the right atrium, normally generates an electrical impulse in the heart. The impulse activates the atria, and then the electrical stimulus continues down the conduction pathway, activating the ventricles. In patients with atrial fibrillation, the electrical stimulus cannot follow the normal pattern because of an underlying disease state such as heart failure or myocardial infarction; additional risk factors for atrial fibrillation include hypertension, diabetes, hyperthyroidism, Wolff-Parkinson-White syndrome, pneumonia, pulmonary embolism, excessive alcohol consumption, smoking, and family history.1 The irregular electrical impulse causes the atria to fibrillate, causing blood to pool in the atria and thereby increasing the patient’s risk of stroke and hemodynamic compromise, including chest pain, pulmonary edema, or syncope.1,5,6Early recognition and treatment of atrial fibrillation are crucial in preventing and reducing the incidence of adverse outcomes such as stroke or thromboembolism.1 A patient may present with fatigue, dyspnea, dizziness, diaphoresis, and palpitations, or they may be asymptomatic.5 Nurses can recognize atrial fibrillation not only by identifying a rapid, irregular heart rate but also by observing the absence of P waves and the presence of fibrillatory waves, a narrow QRS complex, and irregular R-R intervals on an electrocardiogram (Figure 1).1,5Atrial fibrillation is classified according to the duration of episodes.1 Nonvalvular atrial fibrillation, the most common type, occurs in the absence of valvular disease. Paroxysmal atrial fibrillation resolves spontaneously or with intervention within 7 days of onset and may reoccur with variable frequency. Persistent atrial fibrillation lasts longer than 7 days, causing atrial remodeling. Permanent atrial fibrillation has a duration longer than 12 months and the patient and provider accept that sinus rhythm cannot be maintained, so no further attempts will be made to restore it.1,6The duration of atrial fibrillation and the patient’s hemodynamic status largely influence the treatment strategy. Health care providers treat and manage atrial fibrillation according to 3 main goals: prevent thromboembolism, control ventricular rate, and restore sinus rhythm. Almost all patients who have atrial fibrillation receive antithrombotic therapy to reduce the risk of stroke; such therapy is avoided, however, if the patient declines or has contraindications such as advanced age (≥85 years old), intracranial bleeding, thrombocytopenia, or hematological malignancy.7 In patients with atrial fibrillation, the goal is to achieve a heart rate slower than 110 beats/min.1 Heart rate is controlled with b-blockers (propranolol, metoprolol, esmolol, and nadolol) or calcium channel blockers (diltiazem and verapamil).5 Sinus rhythm is restored by eradicating the underlying causes and by using pharmacological or electrical cardioversion (or both).Pharmacological and electrical cardioversion are indicated for patients with atrial fibrillation who do not respond to medical therapy. Pharmacological cardioversion, applied by administering antiarrhythmic medications such as amiodarone, ibutilide, dofetilide, flecainide, and propafenone, is most successful in patients who have developed atrial fibrillation within the preceding 7 days.5,6 Although pharmacological cardioversion may be successful in restoring sinus rhythm, additional efforts are sometimes necessary.Electrical cardioversion is indicated for patients with atrial fibrillation who are hemodynamically unstable or who do not respond to pharmacological therapy. Electrical cardioversion restores sinus rhythm by delivering a synchronized electrical shock when the QRS complex is sensed. The success of electrical cardioversion greatly depends on the amount of electrical energy (joules) administered, the waveform (biphasic or monophasic), and placement of the electrode pads. Historically, monophasic defibrillators were used to conduct electrical cardioversions; however, many institutions have transitioned to biphasic devices. A biphasic waveform is more effective than a monophasic waveform because it uses less energy, resulting in less myocardial dysfunction after the shock, and is insensitive to the changes in transthoracic impedance (the resistance to current flow through the chest).3,4,8The final factor influencing the success of an electrical cardioversion is electrode pad placement. Electrode pads can be positioned either anterior-posterior or anterior-lateral. A nurse prepares a patient for a cardioversion by preparing the skin (ie, removing excess chest hair), attaching monitor leads, and applying electrode pads. If directed to use the anterior-posterior method, the nurse applies the anterior electrode pad at the third intercostal space along the left midclavicular line. The posterior electrode pad is also applied on the left, lateral to the spine and below the scapula at heart level (Figure 2). Figure 3 illustrates anterior electrode pad placement on a female.If directed to use the traditional method of anterior-lateral placement, the nurse places the anterior electrode pad at the third intercostal space along the right midclavicular line, and the second electrode pad at the fifth intercostal space along the left midaxillary line (Figure 4).Proper positioning of the electrode pads is important because the position of the pads determines the shock field gradient—that is, the area of myocardial tissue through which energy travels from the electrode pads. In order to successfully terminate atrial fibrillation, a shock field gradient is essential in the left atrium. Studies have shown that the left atrium and the left pulmonary veins help initiate atrial fibrillation3,9: beats from the pulmonary vein trigger premature atrial contractions, leading to atrial fibrillation. Because the left atrium is positioned behind the right atrium in the thoracic cavity, a posterior electrode pad is necessary to target the left atrium. Anterior-posterior electrode placement best targets both atria.3,9Electrode positioning influences not only the shock field gradient but also transthoracic impedance. Transthoracic impedance, defined above, influences the success of electrical cardioversion. Patients who receive electrical cardioversion through anterior and posterior electrode pads have lower transthoracic impedance than do those who receive cardioversion with pads in the anterior-lateral position.Anterior-posterior electrode pad placement is preferred over anterior-lateral electrode pad placement when performing electrical cardioversion. Electrode pads are placed anteriorly at the third intercostal space along the left midclavicular line and posteriorly at heart level, below the left scapula and lateral to the spine. Electrical cardioversion using anterior-posterior electrode pad placement uses less energy and restores sinus rhythm more quickly than do other methods.