Interpretation of Telemetry Among Patients With a Left Ventricular Assist Device.

Abstract

Scenario: This rhythm strip was obtained on a 45-year-old woman with a medical history of coronary artery disease, prior coronary artery bypass graft, heart failure with reduced ejection fraction, and an implanted left ventricular assist device (LVAD). She arrived at the emergency department with fatigue, weakness, nausea, and vomiting. Her LVAD was operating at a 4.3 L/min flow rate, 5600 rotations per minute (rpm) speed, and 4.2 W of power. Assessment of her vital signs in the emergency department showed low-grade fever, tachypnea (respirations, 20/min), and desaturation (oxygen saturation by pulse oximetry, 92%) on room air. She tested positive for COVID-19 and was admitted to the cardiac LVAD floor. The nurse was concerned about an asystole alarm from the bedside monitor.Sinus rhythm at a heart rate of 69/min, rS morphology in lead II most likely due to left axis deviation, and low QRS wave amplitude. Additionally, an electrical baseline artifact related to LVAD oscillations is apparent in both leads.In patients with an LVAD, the electrocardiogram (ECG) provides essential information such as rate and rhythm; however, excessive electrical artifact and low QRS amplitude impair more advanced ECG interpretation and impact the computerized algorithms, leading to many telemetry alarms.The most pronounced ECG change associated with LVAD implantation is electrical artifact. The electrical artifact on the ECG, seen as many short bold spikes, corresponds to the rotational speeds of the LVAD motor: the faster the motor is rotating, the higher the frequency of the electrical artifact. Commercially available LVADs run at different rotational speeds in 3 ranges: 2400-3200 rpm, 5000-6000 rpm, and 8800-10 000 rpm, corresponding to oscillating frequencies of 40-53.3 Hz, 83.3-100 Hz, and 146.7-166.7 Hz, respectively. The ECG filters are imperfect and are not necessarily designed for noise caused by an LVAD. Most ECG telemetry systems have a filter between 0.05 and 40 Hz, as seen on the telemetry strip.This ECG shows low-amplitude QRS complexes in both leads. QRS complexes with low amplitudes occur after LVAD implantation owing to surgical removal of the myocardium to place the motor, as well as ischemia and inflammation from the procedure. The removal of myocardium also alters myocyte depolarization, which may explain the negative QRS complex in lead II suggestive of a left electrical axis deviation but requiring a 12-lead ECG to confirm.In this case, a combination of electrical artifacts from the LVAD motor and low QRS amplitudes is responsible for the asystole alarm. Modern telemetry systems use computerized algorithms to determine heart rate and rhythm on the basis of the detection of the QRS complex and the R-R interval between successive QRS complexes. Common computerized algorithms for heart rate detection use strict QRS amplitude criteria (ie, unidirectional QRS >5 mm in >2 ECG leads). These algorithms work only on whichever leads are being monitored on the central telemetry monitoring system, in this case, leads II and V1. If the amplitude of the QRS complex is too low to be detected or is obscured by electrical artifact, the algorithms fail to detect the rate and rhythm, subsequently causing the asystole alarm. Although more advanced filters are necessary to filter out the electrical artifact caused by the LVAD motor, repositioning the ECG leads to areas with more myocardium not removed during LVAD implantation will also increase QRS complex amplitude.The most important nursing action with an asystole alarm is to assess the patient; this patient was alert and oriented with good perfusion according to Doppler pressure. Remember, a pulse may not be palpable in LVAD patients. As all potentially emergent findings had been ruled out, the underlying causes for the false asystole alarms could be addressed. To reduce the burden of unnecessary asystole alarms, nurses can change the leads being monitored to see if one lead has less artifact and greater QRS amplitude. Nurses can also move the limb electrodes more centrally toward the heart to increase QRS amplitude and should avoid placing the electrodes over bony prominences or edematous areas, which are associated with reduced QRS amplitude.Current American Heart Association practice standards for in-hospital ECG monitoring provide a class I recommendation for continuous bedside ECG monitoring for patients with an LVAD. However, LVADs are associated with a substantial number of false alarms, and research has shown that few patients have truly actionable alarms. Further research and refinement of clinical standards are necessary.