A new methodological approach to assess cardiac work by pressure–volume and stress–length relations in patients with aortic valve stenosis and dilated cardiomyopathy

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Abstract
In experimental animals, cardiac work is derived from pressure–volume area and analyzed further using stress–length relations. Lack of methods for determining accurately myocardial mass has until now prevented the use of stress–length relations in patients. We hypothesized, therefore, that not only pressure–volume loops but also stress–length diagrams can be derived from cardiac volume and cardiac mass as assessed by cardiac magnetic resonance imaging (CMR) and invasively measured pressure. Left ventricular (LV) volume and myocardial mass were assessed in seven patients with aortic valve stenosis (AS), eight with dilated cardiomyopathy (DCM), and eight controls using electrocardiogram (ECG)-gated CMR. LV pressure was measured invasively. Pressure–volume curves were calculated based on ECG triggering. Stroke work was assessed as area within the pressure–volume loop. LV wall stress was calculated using a thick-wall sphere model. Similarly, stress–length loops were calculated to quantify stress–length-based work. Taking the LV geometry into account, the normalization with regard to ventricular circumference resulted in “myocardial work.” Patients with AS (valve area 0.73 ± 0.18 cm2) exhibited an increased LV myocardial mass when compared with controls (P < 0.05). LV wall stress was increased in DCM but not in AS. Stroke work of AS was unchanged when compared with controls (0.539 ± 0.272 vs 0.621 ± 0.138 Nm, not significant), whereas DCM exhibited a significant depression (0.367 ± 0.157 Nm, P < 0.05). Myocardial work was significantly reduced in both AS and DCM when compared with controls (129.8 ± 69.6, 200.6 ± 80.1, 332.2 ± 89.6 Nm/m2, P < 0.05), also after normalization (7.40 ± 5.07, 6.27 ± 3.20, 14.6 ± 4.07 Nm/m2, P < 0.001). It is feasible to obtain LV pressure–volume and stress–length diagrams in patients based on the present novel methodological approach of using CMR and invasive pressure measurement. Myocardial work was reduced in patients with DCM and noteworthy also in AS, while stroke work was reduced in DCM only. Most likely, deterioration of myocardial work is crucial for the prognosis. It is suggested to include these basic physiological procedures in the clinical assessment of the pump function of the heart.

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