Cardiac response to CRT and heart rate augmentation – The first assessment with CMR

Introduction: Cardiac resynchronisation therapy (CRT) is a routine treatment for heart failure with reduced ejection fraction with conduction delay to improve symptoms and prognosis in patients. Technological advancements both in imaging cardiovascular magnetic resonance (CMR) and devices (sophisticated MRI-conditional modes) enable investigation of the haemodynamic response to CRT over a range of heart rates. Methods: Patients with a CRT-D device were enrolled from heart failure clinics at Leeds General Infirmary, Leeds. After an MRI safety assessment, a baseline device interrogation was conducted by a cardiac physiologist. Left ventricular (LV) volumes and systolic blood pressure were measured at baseline and heart rates of 75, 90, 100, 115, 125 and 140 (randomised order) with CRT active and intrinsic/RV conduction. All scans were conducted using a 3.0 T Siemens Prisma human MRI scanner. Analysis of the scans used commercially available software (cmr42, Circle Cardiovascular Imaging Inc, Calgary, AB, Canada) and manual contouring was completed for LV systole and diastole at each heart rate. A post-scan device interrogation was conducted to assess for scanning safety. Results: In this randomised crossover study, scanning was conducted in 17 patients (Table 1) across the range of heart rates with CRT active and disabled. Post-scan battery voltage from baseline was –2.92 and 2.90% (p=ns) with CRT active and disabled respectively. Overall lead impedance change was –0.1% and 0.91% (p=ns) in patients with CRT active and disabled respectively. No statistical difference was found between CRT modes, furthermore, no patient experienced symptoms related to scanning or device failure. Contractility increases across heart rates when CRT is active whilst relatively static when CRT is disabled. At the peak heart rate of 140 bpm, mean contractility was 2.6 mmHg/mL compared with 1.98 mmHg/mL (p=0.05) when CRT was active and disabled respectively. Other heart rates failed to reach statistical significance in terms of contractility when alternating CRT modes. LVEF is reducing with increased atrial pacing in keeping with cardiac physiology. Mean LVEF was 26.2% versus 19.3% (p