Cardiac Magnetic Resonance in Patients With Cardiac Resynchronization Therapy: Is It Time to Scan With Resynchronization on?

Cardiac resynchronization therapy (CRT) is recommended in international guidelines for patients with heart failure due to important left ventricular systolic dysfunction (or heart failure with reduced ejection fraction) and ventricular conduction tissue disease. Cardiac magnetic resonance (CMR) represents the most powerful imaging tool for dynamic assessment of the volumes and function of cardiac chambers but is rarely utilized in patients with CRT due to limitations on the device, programming and scanning. In this review, we explore the known utility of CMR in this cohort with discussion of the risks and potential benefits of scanning whilst CRT is active, including a practical strategy for conducting high quality scans safely. Our contention is that imaging in patients with CRT could be improved further by keeping resynchronization therapy active with resultant benefits on research and also patient outcomes.

Introduction

In addition to survival benefits, cardiac resynchronization therapy (CRT) can improve symptoms and functional capacity in patients with left ventricular systolic dysfunction and conduction delay.^[1–3] Consequently CRT has a Class 1a level of recommendation in both European and American guidelines for symptomatic patients with prolonged QRS duration on electrocardiogram (ECG) and severe left ventricular systolic impairment.^[4,5]

Cardiac magnetic resonance (CMR) is accepted as the gold standard imaging modality for assessing cardiac volumes, mass and ejection fraction.^[4] Cardiac magnetic resonance also has an important role in the assessment of myocardial fibrosis, ischaemia and viability. The pattern of scarring can be helpful in differentiating the aetiology of heart failure including ischaemic or dilated cardiomyopathy. Cardiac magnetic resonance can also contribute to the diagnoses of rarer conditions such as myocarditis, sarcoidosis, and haemochromatosis. In most of these diseases, the extent of scarring also provides powerful prognostic information.^[6] There are no data to describe the rate of use of CMR in CRT patients either for follow-up or for the diagnosis of other cardiovascular and non-cardiovascular problems, but we expect this is very low.

The advent of magnetic resonance imaging (MRI) conditional pacemakers and devices could offer the exciting opportunity to assess specifically the effect of biventricular pacing on cardiac volumes and function using the most reproducible imaging technique. Indeed the recent joint statement from the British Cardiovascular Society and the Clinical Imaging Board indicates the safety of using CMR in device patients.^[7] However, the majority of devices disable left ventricular pacing when put into the CMR-scan mode. Thus, the images obtained are limited by dyssynchrony associated with the intrinsic underlying conduction delay or right ventricular pacing. Whilst some aspects of left ventricular remodelling can be assessed, the entire dataset must be interpreted with the proviso that the patient is being imaged while in a non-routine rhythm that may negatively impact contractile function and valvular regurgitation.^[8] Ideally, any assessment of cardiac function should take place with CRT enabled. In this review, we consider the role of CMR prior to implantation and how it could be utilized following CRT implantation. – Med Scape