Rick Schreurs

25 Exploring CRT (TAT) of both ventricles, which is characterized by a widened QRS complex on the surface ECG [14]. These findings are similar in dogs [10]. The left panel of figure 2 describes how the dyssynchronous electrical activation of the LV causes the early-activated septum to contract against a reduced load, which leads to pre-stretch of the LV lateral wall (i.e. more positive strain; middle panel, solid line) [14]. This pre-stretch increases contractile force of the LV free wall, which on its turn paradoxically stretches the septum later in systole (positive strain of the septum, striped line). Both types of systolic stretching can be considered wasted work, which is the ratio of negative and positive work (red and black lines respectively; bottom panels) [3, 19]. LBBB Acute CRT 0 0.6 0.2 0.4 mvc avo avc mvo Time (s) 0 0.2 0.4 0.6 mvc avo avc mvo Time (s) 1500 1000 500 0 Work (mmHg·%) 50 100 150 LVP (mmHg) -15 -10 -5 0 Strain (%) Lateral wall Septum Ratio 0.11 Ratio 1.15 Lateral wall Septum Ratio 0.09 Ratio 0.08 Lateral wall Septum Septum Lateral wall Figure 2. Estimated LV pressure (top), strain (middle), and calculation of wasted work for the septum and lateral wall (bottom) in a representative patient with left bundle branch block (LBBB; left) and after treatment with cardiac resynchronization therapy (CRT; right). Vertical lines indicate valvular events defined by echocardiography. Negative and positive work during systole is marked as red and black, respectively. Wasted work ratios were calculated using cumulated work between the closure and subsequent opening of the mitral valve (MVC and MVO, respectively). AVO: aortic valve opening, AVC: aortic valve closure. Reproduced with permission from the American Physiological Society [19]. In canine hearts, the maximum rates of rise and fall of the LV pressure (dP/dt max and dP/ dt min ) decrease immediately upon creating LBBB and this decrease is still present after 8 weeks. Echocardiographic follow-up shows an increase of end-diastolic and end-systolic volume and decrease of ejection fraction with longer lasting LBBB [3]. These findings 2