Heart failure: re-evaluating causes and definitions and the value of routine cardiac magnetic resonance (CMR) imaging

Abstract

Objective
To differentiate the demographics and imaging characteristics of a heart failure population using a comprehensive echocardiographic protocol and routine CMR imaging, and to assess the clinical value of routine CMR in this population.

Methods
A novel comprehensive diagnostic pathway for heart failure was prospectively applied to 319 new patients attending the Darlington and Bishop Auckland heart failure clinic between May 2013 and July 2014. All had a full clinical assessment and an initial basic clinical transthoracic echo performed. Those patients given a diagnosis of heart failure went on to have routine CMR imaging as well as a more detailed echo scan incorporating a variety of systolic and diastolic measurements.
Retrospectively, a cohort of 116 patients with left ventricular systolic impairment, that had both CMR and invasive coronary angiography, were analysed to determine the ability of late gadolinium enhancement (LGE) CMR to predict prognostic coronary artery disease.

Main results
1. Heart failure with reduced ejection fraction (HFREF) accounted for the cause of heart failure in 73% of cases whereas heart failure with preserved ejection fraction (HFPEF) accounted for only 14% of cases.
2. Incorporating CMR into the routine assessment of newly diagnosed heart failure patients changed the diagnosis in 22% of cases (14% of cases for those who had an echo performed on the same day).
3. CMR left ventricular ejection fraction (LVEF) averages 3.9% units higher than Simpson’s Biplane LVEF with echo.
4. Regional wall motion score (RWMS) equations were inferior to a Simpson’s Biplane assessment of LVEF by echo and cannot be advocated for routine clinical use.
5. The presence of subendocardial LGE on CMR demonstrated infarcts in 42% of those with HFREF, 20% of those with HFPEF, and 40% of those with heart failure with no major structural disease (HFNMSD).
6. The absence of subendocardial LGE excluded prognostic coronary disease in 100% of cases.
7. LGE in a non subendocardial distribution was prevalent in both the HFREF and HFPEF community with a greater average burden in the HFPEF group.
8. E/e’ and left atrial volume index (LAVI) were the most helpful echo measures for a positive diagnosis of HFPEF and could be measured in over 90% of cases.
9. Systolic dysfunction out with reduced ejection fraction is present in 76% of the HFPEF cohort.

Conclusion
Heart failure with preserved ejection fraction (HFPEF) is not the epidemic previous literature would have us believe. It is over-diagnosed in current practice due to lax definitions and inappropriately low left ventricular ejection fraction (LVEF) cut-offs.
CMR has a substantial impact on the diagnostic profile of the heart failure population. It revokes the diagnosis of HFREF to a greater extent than is accounted for by the temporal improvement in LVEF, even when taking into account method specific LVEF thresholds. CMR with LGE has additive value for identifying infarcts in a sizeable number of patients for whom there is no suspicion of ischaemic heart disease (IHD), and raising the novel concept that ischaemia may account for symptoms in many of those with HFNMSD. It also demonstrates an impressive ability to exclude prognostic coronary disease. Additionally, LGE in a non subendocardial distribution establishes aetiology including myocarditis and sarcoidosis that would not be detected with echo alone.
The diagnosis of heart failure with preserved ejection fraction is not standardised and all current protocols are deficient. The cause and mechanism of this condition remains unclear and this study helped clarify the contribution of systolic versus diastolic dysfunction versus simply the presence of atrial fibrillation. Key diagnostic parameters were identified for routine clinical use and CMR LGE imaging demonstrating a greater average burden of non subendocardial LGE may support the postulated fibrotic infiltrative mechanism of pathology in this group.