Assessment of wasted myocardial work: a novel method to quantify energy loss due to uncoordinated left ventricular contractions

Abstract

Left ventricular (LV) dyssynchrony reduces myocardial efficiency because work performed by one segment is wasted by stretching other segments. In the present study, we introduce a novel noninvasive clinical method that quantifies wasted energy as the ratio between work consumed during segmental lengthening (wasted work) divided by work during segmental shortening. The wasted work ratio (WWR) principle was studied in 6 anesthetized dogs with left bundle branch block (LBBB) and in 28 patients with cardiomyopathy, including 12 patients with LBBB and 10 patients with cardiac resynchronization therapy. Twenty healthy individuals served as controls. Myocardial strain was measured by speckle tracking echocardiography, and LV pressure (LVP) was measured by micromanometer and a previously validated noninvasive method. Segmental work was calculated by multiplying strain rate and LVP to get instantaneous power, which was integrated to give work as a function of time. A global WWR was also calculated. In dogs, WWR by estimated LVP and strain showed a strong correlation (r = 0.94) and good agreement with WWR by the LV micromanometer and myocardial segment length by sonomicrometry. In patients, noninvasive WWR showed a strong correlation (r = 0.96) and good agreement with WWR using the LV micromanometer. Global WWR was 0.09 ± 0.03 in healthy control subjects, 0.36 ± 0.16 in patients with LBBB, and 0.21 ± 0.09 in cardiomyopathy patients without LBBB. Cardiac resynchronization therapy reduced global WWR from 0.36 ± 0.16 to 0.17 ± 0.07 (P < 0.001). In conclusion, energy loss due to incoordinated contractions can be quantified noninvasively as the LV WWR. This method may be applied to evaluate the mechanical impact of dyssynchrony.

Application of three-dimensional speckle tracking echocardiography to assess left ventricular regional work using wall tension-regional area loop

“…There are a lot of situations where measurement of not only total but also regional work is desired. For example, T-A loop analysis might give us insight into how different therapeutic principles including medications modify myocardial function and how interventions like ventricular pacing change regional work at the pacing site (5,16,18). In a patient with left bundle branch block, the early activated segments produce little or negative work, whereas the late-activated segments produce more work than normal segments.…”

“…three-dimensional echocardiography; pressure-volume loop; cardiac function; ventricular work LEFT VENTRICULAR (LV) systolic function is commonly assessed with ejection fraction or fractional shortening in clinical practice. However, they are only a global index, and there is sometimes a clinical need of assessing regional function such as in myocardial ischemia and LV dyssynchrony (18). Heterogeneous contraction of the LV even in a healthy subject also prompted us to assess regional function in a quantitative manner (12,29).…”

Cardiac resynchronisation therapy: current indications, management and basic troubleshooting

“…At the end of the QRS, the LV lateral wall contraction pushes against a relaxing LV septum. The result of this failure in contraction sequencing is that mechanical energy is wasted by ‘internal work’ as one LV wall alternately pushes on the other 5. Another consequence of dyssynchrony is in loss of economy in the cardiac cycle.…”

Impact of Cardiac Resynchronization Therapy on Left Ventricular Mechanics: Understanding the Response through a New Quantitative Approach Based on Longitudinal Strain Integrals

“…Our study concentrated on strain integrals, taking into account their accumulated dynamics, which are neglected when analyzing strain peaks alone. To our knowledge, only the recent work by Russell et al 30 also focused on a more detailed analysis of strain signals, estimating the amount of physical work performed by each LV segment. Although preliminary results of this method are encouraging, it requires a comparative large prospective and multicenter evaluation.…”