QAOS Protocol: an echocardiographic strategy for the assessment of pacemaker-induced cardiac dyssynchrony

Abstract The ventricular activation front generated by a pacemaker resembles that of advanced left bundle branch block, with delayed electromechanical activation of the left ventricular free wall. This leads to contraction dyssynchrony and, eventually, heart failure. Evidence supports the existence of a distinct clinical entity known as Paced-Induced Cardiomyopathy (PIC), defined by the 2023 HRS/APHRS/LAHRS guidelines as a decrease in left ventricular ejection fraction (LVEF) to below 50%, with an absolute decrease in LVEF greater than 10%, a pacing burden of at least 20%, and no other identifiable causes of heart failure following device implantation. This paper proposes a protocol named QAOS ( Quick Assessment Of Synchrony ) for evaluating patients with an existing pacemaker (to enable follow-up and early diagnosis of PIC), and for patients undergoing resynchronization or physiological pacing (His bundle or left bundle branch), to assess whether synchrony has been restored. The protocol consists of ten steps that follow the sequence of a standard echocardiographic study, and it does not require highly specialized techniques. The primary objective of this publication is to encourage the development of pilot studies across different centers devoted to the care of patients with pacemakers — and, if these studies’ value and clinical applicability are demonstrated, to enable the protocol’s evaluation in clinical trials.