2.2 Clinical Data and Measurements
Data collection was done by reviewing the electronic medical records. Patient characteristics, indications, pre-implantation medical details, electrocardiographic (ECG), echocardiographic (ECHO) findings, and procedural details were reviewed. Intrinsic QRS duration was defined as the duration of conducted QRS (or escape QRS in case of no conducted beats) in the pre-implantation ECG. QRS complexes were classified according to duration and morphology using the standard criteria established by American Heart Association and Heart Rhythm Society expert consensus document (11). Ejection fraction(EF) was calculated using Simpson’s method and other echocardiographic parameters were acquired according to American Society of Echocardiography and European Society of Echocardiography expert consensus document (12). The site of ventricular lead placement was ascertained from the procedural notes which was further confirmed from chest radiograph and classified as apical or non-apical based on the location. PM parameters were noted at discharge and at end of follow up period. RV pacing % burden was recorded at end of follow up period or earlier if the primary outcome of PICM was reached. Paced QRS duration was measured from the immediate post pacemaker insertion electrocardiogram. PICM was defined as a fall in post implant LVEF by 10 percentage points to a LVEF of less than 50.0 % from baseline due to RV pacing in the absence of other known causes of cardiomyopathy.