Transvenous pacing is typically the most effective therapy for unstable bradycardia but it is invasive, takes some time to perform, and is a procedure for which many acute care physicians lack comfort and significant experience. Transcutaneous pacing (TCP), on the other hand, is fast, easy to perform, and tends to be well tolerated by most patients when they receive appropriate doses of analgesia.
Unfortunately, TCP often fails to produce electrical or, more importantly, mechanical capture. Oftentimes when capture initially fails, the electrical current is increased in hopes of gaining capture but much to the discomfort of the patient. Increased body mass index can contribute to failure to capture, but what about TCP pad position? Despite recommendations for TCP in the United States and European resuscitation guidelines for many years, until now, no studies have evaluated optimal pad position for TCP. As a result, the default position for most clinicians using TCP has been the anterior-lateral (AL) position on the chest wall.
A study published in October 2022 compared the common AL position (anterior pad placed at the right upper chest and lateral pad placed over the left lower rib cage at the mid-axillary line) with the anterior-posterior (AP) position (anterior pad placed on the left chest over the apex of the heart and the posterior pad on the left mid-back area approximating the level of the mid-portion of the heart). The AP position has become more commonly used in defibrillating arrested hearts because it more accurately sends the current through the left ventricle. The concern with the AL position, especially in patients with large body habitus, is that the vector of the current may partially or entirely miss the left ventricle.
Moayedi and colleagues hypothesized that optimal TCP should employ pad placement that is similar to that used during optimal defibrillation attempts. They conducted a study comparing AL versus AP position during TCP and published their results in two parts, which will be discussed together.
The investigators evaluated 20 patients (6 women, 14 men) who had elective cardioversion of atrial fibrillation in the electrophysiology lab (Resuscitation. 2022 Dec;181:140-6). After successful cardioversion to sinus rhythm, the cardioversion pads were removed, and two new sets of pacer pads were placed on the patients’ chests. Pads were placed in both the AL and the AP positions, as previously described. Starting at a current output of 40 mA, the output was slowly increased on one set of pads until mechanical capture was obtained at the same rate as the pacer setting for at least 10 seconds. Pacing was then discontinued, but then the process was repeated using the second set of pads. The order in which the positions were tested (that is, AL tested first vs. AP tested first) was alternated. If capture was not obtained by 140 mA (the pacer’s maximum output), failure to capture was documented. Both positions were tested in all patients except for three cases where the second position was not tested because of inadequate analgesia.
The investigators found that 8 in 19 (42%) of the AL trials and 14 in 18 (78%) of the AP trials successfully captured. For the 17 participants who completed both trials, both positions captured in 8 in 17 (47%). AP but not AL was captured in 5 in 17 (29%); AL but not AP was captured in 0 cases. Neither position captured in 4 in 17 (24%). Of note, there was no association between successful capture and body mass index, chest circumference, or chest diameter. The AP position was more successful in both women and men, compared with the AL position. The investigators also found that, among the successful trials, the AP position tended to capture at lower currents than the AL position (93 mA vs. 126 mA).
In summary
TCP is a potentially lifesaving intervention in the treatment of patients with unstable bradycardia. Many of us who have attempted to perform TCP on unstable patients have frequently been disappointed with the results. In retrospect, however, I can recall that each time I have attempted this procedure, it has been using pads placed in the AL position.
Now for the first time we have data indicating that the standard AL position may be suboptimal, compared with the AP position. The study by Moayedi and colleagues is small, but the results are compelling, and the AP pad placement intuitively makes more sense. By using the AP pad placement, which provides greater likelihood of electrical current passing through the left ventricle, we should expect a greater likelihood of successful capture during attempts at TCP. In addition, we may anticipate lower analgesia needs if the AP position requires less current for success. Kudos to Moayedi and colleagues for performing a novel study of a critical procedure in acute care medicine.
Amal Mattu, MD, is a professor, vice chair of education, and codirector of the emergency cardiology fellowship in the department of emergency medicine at the University of Maryland, Baltimore. He had no disclosures. A version of this article first appeared on Medscape.com.