Standard and extended electrocardiographic screening for the subcutaneous implantable cardioverter-defibrillator
Authors: Lewandowski M , Syska P , Kowalik I 
Published: May 2023

Abstract

Funding Acknowledgements
Type of funding sources: None.

Background
The subcutaneous implantable cardioverter-defibrillator (SICD) is effective therapy for sudden cardiac death prevention. The condition for implantation is an electrocardiographic screening test before procedure (ECG-s). Patients who don’t pass are regarded to be at risk of inappropriate detection of tachyarrhythmias with inappropriate interventions. A patient is considered suitable for implant if at least one surface ECG lead (sense vector) is acceptable for all tested postures.

Objective
The aim of the study was to identify the incidence of failure, the predicting factors and clinical importance of extended ECG-s with right sided lead position and lying on the left and right side of the body.

Methods
ECG-s to determine suitability for SICD is based and performed using a manufacturer –specific measurement tool. We performed this test in 75 consecutive pts with indication for SICD therapy on the basis of standard manufacturer protocol(lead at the left sternum border: sitting, standing and lying position), and extended for right sternal lead location and two additional body position: lying on the left and right side (10 position for each individual). We analyzed: age, gender, body mass index(BMI), heart rate, heart rhythm(sinus/atrial fibrillation), QRS duration, PR interval, corrected QT interval(QTc), echocardiography parameters, etiology.

Results
ECG-s failure occurred in 6/75(8%) of patients. Screening results: 1 vector failure rate with the standard device and lead positions: primary(P) 12%, seconadary(S) 17%, alternative(A) 40%, P vs. A and S vs. A p&lt;0,001. Testing with an electrode positioned on the right sternum border- 1 vector failure: (P) 10%,seconadary(S) 17%, alternative(A) 48%, P vs. A and S vs. A p&lt;0,001. In case of failure on left side 50%, 14% and 6% of pts passed the test with the right sided lead position for P, S and A vector respectively, p&lt;0.001. Identified factors predicting ESG-s passing vs. failure included: QTc interval 445,32±35,4 vs. 480,6±37,6 ms for any vector(p=0,034), BMI:26,7±4,7 vs. 29,9±4,7 for vector A( p=0,008 ), EF: 43,3±20,1 vs. 34,0±16,2 for vector A( p=0,027).
Sense vector failure rate with the left sternal lead location lying on the left and right side of the body was concordant with the rate lying on the back, p=0,05. For the right parasternal lead location the rate failure was lower lying on the right side for all sense vectors: P, S and A(p=0,045; 0,083 and 0,020) respectively.

Conclusions
ECG screening failure rate for SICD is comparable with previous reports. The right sternal lead location screening is effective and enables important clinical findings before implantation and in case of lead reposition( defibrillation threshold test failure) during procedure. We recommend to screen routinely on both sternum borders. Some additional body position testing: lying on the left and right side of the body, mimicking sleeping/rest could be an important element to determine eligibility for SICD.