Dr. Ole A Breithardt
The principle of cardiac resynchronisation therapy (CRT) is based on the presence of an electrical conduction delay which results in a significant amount of dyssynchronous myocardial contraction leading to impaired hemodynamics and ventricular remodeling. Several published clinical guidelines provide clear recommendations with respect to the CRT indications, which are mainly based on clinical and electrocardiographic criteria. However, patient selection remains a divisive and debated topic, because the overall response rate to this invasive and relatively costly therapy is still imperfect, with clear potential for further improvement. Despite some disappointing study results, most experts still believe that cardiac imaging should be able to overcome these limitations and add important new mechanical information to the ECG, in order to improve the acute and long-term response rate to CRT.
In the first presentation of this “Read with the Experts” seminar, Erwan Donal (Rennes, France) emphasized that assessment of mechanical dyssynchrony is just one of the multiple parameters that have to be assessed by echocardiography before CRT. He stressed that it is equally important to determine right and left ventricular size and function, valvular morphology and myocardial viability. With respect to dyssynchrony assessment, he demonstrated that single dyssynchrony parameters as used in trials such as the PROSPECT study may not sufficiently characterize the complete spectrum of dyssynchrony and that an integrative multi-parameter approach is preferable. Among the different echo techniques, he particularly valued the assessment of myocardial deformation (strain) by 2D speckle tracking techniques, which make it possible to assess the extent of inefficiently contracting myocardial segments. Peter Sogaard (Copenhagen, Denmark) gave the second lecture. He first discussed the clinical value and limitations of QRS width for patient selection. He illustrated very elegantly that the patient subgroup with a QRS width in the lower range below 150ms are those who will benefit the most from additional assessment of dyssynchrony by imaging modalities, as the ECG has only very limited specificity in this population. The main aim for identification of dyssynchrony by imaging is to lower the number of unnecessary implants in patients with a QRS below 150ms and to avoid some unnecessary implants in patients with wider QRS width. He then went on to discuss the available echocardiographic parameters in more detail. One of the main conclusions of his presentation was that the “time-to-peak” measures in tissue Doppler imaging (quantifying the sepal-lateral delay in time to peak systolic velocities etc) are often misleading and that a more detailed cross-correlation comparison of the myocardial velocity waveforms that incorporates the velocity information throughout the complete cardiac cycle is more precise in the identification of true correctable myocardial dyssynchrony. He further stressed that additional imaging techniques, such as cardiac magnetic resonance imaging, add important information in the presence of scarred tissue and preserved viability. Integrating these techniques will further improve the selection process. Finally, Christopher Piorkowski (Leipzig, Germany) discussed the relevance of the coronary venous anatomy for successful delivery of CRT. Sufficient resynchronisation of ventricular contraction can only be achieved if the implanter succeeds in positioning the left ventricular lead close to the area of latest electrical activation and mechanical contraction. Often, entry into the coronary sinus can be a challenge and an ideal target vein in the area of presumed latest activation and contraction might not be accessible. Several case examples highlighted the various challenges for the implanter and illustrated the need for pre-implant assessment of the coronary venous anatomy. Myocardial dyssynchrony patterns assessed by real-time 3D echocardiographic assessment can be directly compared to the coronary venous anatomy by image registration techniques and may help to find the best implantation strategy.
The panel concluded that imaging modalities such as echocardiography, magnetic resonance imaging and also invasive angiographic methods continue to play an important role in the daily treatment of CRT patients. This starts with the selection process, continues with the procedural planning and finally makes it possible to assess the efficacy of CRT after implantation, with the possibility to intervene in cases of non-response to CRT.
Cardiac resynchronisation therapy: optimising patient selection with imaging
Corresponding Author: Priv.-Doz. Dr. med. Ole-A. Breithardt Medizinische Klinik 2 Universitätsklinikum Erlangen Ulmenweg 18 DE-91054 Erlangen Germany
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