Work efficiency and diastolic function

It is well known that the work performed by the heart can be estimated as the area of the pressure-strain loop. This project in WP5 builds on a background invention of a method to estimate LV pressure non-invasively and thereby enable estimates of myocardial work as a function of time for each segment in the heart. A further development of these ideas has resulted in the principles of Wasted Work Ratio (WWR). Left ventricular WWR is a method which quantifies the negative impact of dyssynchrony and discoordination on cardiac function and myocardial energy consumption. WWR may serve as a means to identify patients who will benefit from cardiac resynchronization therapy (CRT) and may also serve as a marker of severity of heart failure.

 

SELECTED PROJECTS

Regional Myocardial Work by Magnetic Resonance Imaging and Noninvasive Left Ventricular Pressure: A Feasibility Study in Left Bundle Branch Block
Larsen CK, Aalen J, Stokk C, Fjeld JG, Kongsgaard E, Smiseth OA, Hopp E

We aimed to determine if regional myocardial work can be measured clinically by MRI and non-invasive LV pressure, and to test the feasibility of this approach in left bundle branch block (LBBB).
Regional work was estimated according to the principle of Russell et al. (European Heart Journal, 2012), which is based upon an estimated LV pressure curve in combination with strain. The durations of the different cardiac phases were measured by valvular event timing, and the normalized standard LVP curve was adjusted according to the measured phase durations. The amplitude of the estimated LV pressure curve was scaled by the patient’s systolic brachial cuff pressure, which was used as a surrogate for peak LVP.

By definition, work during myocardial shortening is positive and work during lengthening is negative. Net work is the sum of positive and negative work. We concluded that strain by FTMRI in combination with noninvasive LV pressure demonstrated marked asymmetry in distribution of segmental work in patients with LBBB. Work distribution corresponded well with regional glucose metabolism.

These results imply that strain by FTMRI (functional tracking magnetic reconance imaging) in combination with non-invasive LV pressure is feasible as a clinical tool to measure regional myocardial work.

PhD fellow Camilla K. Larsen in front of her poster at AHA Scientific Session in New Orleans, Louisiana, USA.

 

Contractile Reserve In Dyssynchrony – the CRID-study
Cooperation between Oslo University Hospital (Norway), Rennes University Hospital (France), OLV Hospital Aalst (Belgium), Karolinska University Hospital (Sweden) and University Hospitals Leuven (Belgium).

As previously validated in our laboratory, left ventricular pressure (LVP) can be measured non-invasively using peak systolic blood pressure as a surrogate for peak LVP. An index of regional myocardial work can thereby be calculated as the area of the pressure-strain loop, where strain is obtained by speckle-tracking echocardiography. In the multicenter CRID-study, the distribution of regional myocardial work in the LV is studied as a potential tool to determine CRT-response.

Constructive work when the segment shortens is compared to wasted work when the segment lengthens and the work efficiency (WE) can be calculated as the relationship between these two. A low WE indicates an ineffective contraction and hence a large potential for recovery with CRT. To determine myocardial viability and metabolism CMR and FDG-PET are also performed.

The study has now included 140 patients at five different locations (Oslo, Leuven, Rennes, Aalst and Stockholm). Inclusion is expected to be finished in August 2017 with follow-up for one additional year.

PhD fellow John Aalen in front of his poster at the CHFR Symposium at Holmenkollen, Oslo in September 2016.

Heart SFI