We have developed a novel technique for the assessment and optimization of resynchronization therapy. Our approach is based on transthoracic dynamic three-dimensional (3D) echocardiography and allows determination of the most delayed contraction site of the left ventricle (LV) together with global LV function data. We use a self-developed fast rotating transducer, which is connected to a commercially available ultrasound system (GE Vingmed Vivid FiVe, Horton, Norway). The 64-element phased-array transducer has a center frequency of 3 MHz, second harmonic capabilities and continuously rotates inside the transducer assembly at 8-revolutions/ sec. During resynchronization device implantation, images are obtained with the patient in the left lateral decubitus position with the transducer in the apical position and the image plane rotating around the LV long axis. Images are acquired in sinus rhythm and in two different pacing modes: during right ventricular apical pacing and biventricular pacing. With a self-developed software, using MatLab (The MathWorks, Inc, Natick, MA, USA), the original 2D images are post-processed by placing them in their correct spatial and temporal (ECG reference) position using multi beat data fusion. All the cross-sectional images re-sampled from each dataset are subsequently imported into the TomTec® 4D LV-analysis software (TomTec® Imaging Systems GmbH, Germany) for automated endocardial border detection.
Subsequently, the program performs a dynamic surface rendered endocardial reconstruction of the LV in sinus rhythm and in the different pacing modes. For each pacing mode, a time volume curve (TVC) is plotted from which global end-diastolic (LVEDV), end-systolic volumes (LVESV) and ejection fraction (EF) are calculated. The LV endocardial surface is subdivided in 16 segments, which are color-coded for orientation. The difference in time to maximal myocardial contraction between segments is used to assess and measure regional mechanical delay and dyssynergy (Movies 1, 2 and 3 – see additional file 1
, additional file 2
and additional file 3
Our initial results suggest that fast reconstruction of the LV is feasible for the selection of the optimal pacing site and allows identifying LV segments with dyssynchrony. Additional hemodynamic evaluation is also possible (Movies 1, 2 and 3). Currently, the LV reconstruction is still off-line. However, real time three-dimensional echocardiography is now available, and the optimal pacing site can be determined on-line.