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Dr. Massimo Lombardi ,
The increasing number of heart failure patients needs new diagnostic procedures to optimise the individual therapeutical strategy. Among the different imaging modalities, CMRI might have an added value for a better evaluation of these patients.
Diastolic heart failure is a clinical syndrome characterized by symptoms and signs of heart failure, in spite of a preserved left ventricular ejection fraction. This syndrome is quite common (about one third of heart failure patients) and causes morbidity and health care costs rival to those associated with systolic heart failure. Although mortality rate among these patients is about one half with respect to systolic heart failure, it remains five times higher than in age matched controls. Risk factors are mainly hypertension, aging, diabetes, left ventricular hypertrophy, coronary artery disease. Primitive and acquired cardiomyopathies with restrictive haemodynamic pattern are rare but paradigmatic of diastolic dysfunction. Why diastolic heart failure has higher prevalence in women and blacks still remains unclear.
Proving the diagnosis of diastolic heart failure (or diastolic dysfunction) by the documentation of specific cardiac alterations remains a challenge, as routine use of catheterization, the actual gold standard for demonstrating diastolic impairment on the basis of pressure/volume relationship, is not feasible on a large scale.
As a result, controlled clinical trials on diastolic heart failure are still lacking mainly due to the difficulty in their design. At present the diagnosis of diastolic dysfunction relies on Doppler imaging of trans-mitral flow. However echocardiographic findings must be interpreted in the context of preload, afterload, heart rate and systolic function. Increased levels of natriuretic peptides, in the absence of systolic dysfunction, are suggestive of diastolic heart failure. While the increasing of natriuretic peptides plasma levels is correlated with worsening of clinical prognosis this does not clarify the cause of diastolic impairment. Cardiovascular Magnetic Resonance Imaging (CMRI) is emerging as an alternative, non-invasive, non ionising technique with the unique capability of 3-dimensional functional imaging, great accuracy and reproducibility. This is of great relevance as diastole is a 3-dimensional process (with contemporary rotation, translation and radial motion of the heart). In a recent article, Paelink and Coll reviewed the clinical application of CMRI for the analysis of diastolic function.
Briefly, each echocardiographic parameter useful for the study of diastole can be accurately measured with CMRI, by means of different imaging techniques such as: gradient–echo to evaluate functional dimensions; phase contrast to measure flow; myocardial tagging to assess myocardial regional dynamics. At present, flow measurement has a duration of 12-20 sec, and the result represents the average flow during the acquisition period. Furthermore, the assessment of flow dynamics by CMRI does not suffer of windows limitation and is less dependent on operator’s skill. A typical CMRI examination which accurately assesses cardiac function and flow, requires a scanning time of about half an hour. The strongest technical limitations are the presence of arrhythmias and the need of patients’ cooperation. Furthermore, the cost of CMRI examination cannot be neglected.
CSPAMM (complementary spatial modulation of magnetization), also known as Tagging, is a method well suited for the quantification of diastolic heart wall motion: it allows the detection of the rapid untwisting (clockwise at the apex, counterclockwise at the base during diastole) during isovolumic relaxation, which is followed by the filling phase, where practically no rotational component is present. In hypertrophic athlete’s heart neither the apical peak rotation angle nor the diastolic untwisting are changed when compared with normal controls. Conversely, preliminary findings suggest that patients with aortic stenosis or left ventricular hypertrophy due to pressure overload show a completely different apical rotational pattern.
The main problem of Tagging MRI remains the post-processing evaluation of images. In fact, once the images have been acquired their simple evaluation by an expert operator is not enough for such a purpose and a demanding approach is still required, both in terms of time and automated computerised analysis. Recent advances in post-processing such as HARP analysis considerably reduce these problems and might lead to a routine use of Tagged images.
Nowadays, published series of patients assessed for diastolic function with CMRI consist of a total of 253 pts: 75 with coronary artery disease, 64 with hypertrophic cardiomyopathy, 34 with aortic stenosis, 20 with left ventricular hypertrophy due to pressure overload, and 60 affected by various congenital heart diseases. At present CMRI lacks of reference values for diastolic characterization both in normal and pathological conditions. However, it seems to be the most promising technique for a precise characterisation of wall motion dynamics in patients with diastolic dysfunction.
We do not have yet enough methodological knowledge and diffuse expertises for planning routine evaluation of patients with suspected isolated diastolic dysfunction with CMRI. Nevertheless, the role of CMRI will likely increase for diagnostic and research purposes, as well as for therapeutical trials.
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.
Dr. M. Lombardi, MD Pisa, Italy Director of Cardiovascular Magnetic Resonance LaboratoryC.N.R., Clinical Physiology Institute
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