This article appears in the following Europace issue: Spotlight Issue: Cardiac Imaging in EP and CRT [View the issue table of contents]
IMAGING IN CRT
Imaging in cardiac resynchronization therapy: what does the clinician need?
1 Department of Cardiology, University Hospital Nancy, France; 2 Department of Cardiology, University Hospital Rennes, France
* Corresponding author. Département de Cardiologie et Maladies Vasculaires, Centre Cardio-Pneumologique, Hôpital Pontchaillou, 2 rue Henri Le Guilloux, 35033 Rennes Cedex 09, France. Tel: +33 2 99 28 25 25; fax: +33 2 99 28 25 10. E-mail address: erwan.donal{at}chu-rennes.fr
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Abstract |
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In the guidelines, criteria to select patients for cardiac resynchronization therapy (CRT) are based only on the QRS duration on surface electrocardiogram (ECG) as a marker of cardiac dyssynchrony. From a theoretical point, imaging techniques would be useful to improve patient's selection with an analysis of the atrio-ventricular, interventricular and intraventricular dyssynchrony. Imaging techniques may also identify physiopathological issues such as the presence of scar, right ventricular dysfunction, or severe pulmonary hypertension. New echocardiographic techniques appear promising, but the role of echocardiography in the identification of mechanical dyssynchrony remains to be clearly defined in prospective multicentre trials. The positioning of left ventricular lead could be optimized using different imaging techniques to assess the site of latest activation and the coronary sinus anatomy. Finally, imaging techniques may have an important role to optimize the programming of the device, especially the different cardiac timings. In the present article, we focused on echocardiography, multislices-computed tomography, and magnetic resonance imaging being discussed elsewhere.
Key Words: Cardiac resynchronization therapy, Imaging, Echocardiography, Heart failure
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Introduction |
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Cardiac resynchronization therapy (CRT) associated or not with ventricular defibrillation capabilities is now recommended in selected patients with moderate or severe heart failure.1
The current guidelines were implemented using the inclusion criteria of the majority of the randomized clinical trials that validated CRT. All these trials considered only patients with severe heart failure, left ventricular ejection fraction (LVEF) 
35%, and a wide QRS complex (as marker of cardiac dyssynchrony).1 The definition and/or the evaluation of cardiac dyssynchrony are still a matter of debate. Historically, CRT was developed by electrophysiologists and naturally the criterion to define cardiac dyssynchrony was an electrical parameter, namely the QRS duration on the surface electrocardiogram (ECG).1 This choice was based on the fact that conduction disorders were observed in 30–50% of the patients with severe heart failure and depressed left ventricular function and that conduction disorders may enhance mechanical dyssynchrony.2 Interestingly, the cut-off value of QRS duration decreased over time from 150 ms in the MUSTIC trial to 120 ms in the CARE-HF trial.3,4 Accordingly, the current guidelines identified a QRS width of 120 ms or more as the marker of cardiac dyssynchrony to select patients who are candidates for CRT. The choice of the QRS width as a criterium of cardiac dyssynchrony is often criticized for several reasons: - There is no precise definition for measurement of QRS duration. In the different trials, recommendations to measure the QRS width were only provided in the MUSTIC and CARE-HF trials, and both trials provided different recommendations.3,4
- The QRS width is a marker of electrical dyssynchrony and may not accurately reflect the extent of mechanical dyssynchrony; indeed different studies have shown the lack of correlation between mechanical dyssynchrony assessed by imaging techniques and electrical dyssynchrony assessed by the surface ECG.5–7
- And finally, when QRS duration is used as a cut-off criterium for selection for CRT, a high number of ‘non-responders’ are encountered, and despite technical improvements in devices and implantation techniques, the rate of non-responders is being estimated around 30%.8
First, selection of patients based on the QRS duration is not optimal. Many reports in the literature suggested that the QRS duration is not predictive for response to CRT8 and it is believed that not electrical but rather mechanical dyssynchrony is important for response to CRT. Classically, cardiac dyssynchrony has three components: atrio-ventricular (AV), interventricular, and left intraventricular dyssynchrony,9 and it has been suggested that the presence of left ventricular dyssynchrony is most important for response to CRT. Various observational studies, mainly based on echocardiographic techniques, demonstrated that the correlation between the QRS duration and left ventricular mechanical dyssynchrony was weak.5–7 The same echocardiographic studies also demonstrated that the selection of patients based on the presence of mechanical left ventricular dyssynchrony significantly improved the percentage of responders and that mechanical dyssynchrony was a strong predictive factor for response to CRT.5–8 Accordingly, the first part of information that is needed in CRT is: the presence and extent of left ventricular dyssynchrony. The main problem with left ventricular dyssynchrony is that many different echocardiographic approaches have been reported, with many different cut-off criteria for substantial left ventricular dyssynchrony.10 The majority of these approaches are based on tissue Doppler imaging and/or strain techniques and were developed in expert centres. To define which parameter was best for assessment of cardiac dyssynchrony, the PROSPECT trial was designed.11 This trial tested the performance of 12 different echocardiographic parameters to assess cardiac dyssynchrony and to predict CRT response, which was defined by a clinical composite score and a reduction 
15% in left ventricular end-systolic volume.11 Various echocardiographic approaches demonstrated modest, but statistically significant value for prediction of response to CRT, whether the clinical composite score was used as an endpoint or the reduction in left ventricular end-systolic volume. Importantly, however, the predictive value of all echocardiographic approaches was modest, with limited reproducibility of these approaches. Accordingly, it was concluded that: ‘Despite promising preliminary data from prior single centre studies, echocardiographic measures of dyssynchrony aimed at improving patient selection criteria for CRT do not appear to have a clinically relevant impact on improving response rates when studied in a multi-centre setting such as PROSPECT. Thus, at present the echocardiographic parameters assessing dyssynchrony do not have enough predictive value to be recommended as selection criteria for CRT beyond current indications.’ The hope is that novel technologies such as 2D strain and 3D echocardiography will have superior reproducibility, with higher accuracy to predict response to CRT. Moreover, alternative imaging techniques (e.g. magnetic resonance imaging, gated SPECT imaging) may also prove useful in the assessment of left ventricular dyssynchrony and prediction of response to CRT.12,13 Not only the presence of left ventricular dyssynchrony is information that the clinician needs, but also the site of latest mechanical activation is important. Preliminary data suggest that positioning of the left ventricular pacing lead outside of the site of latest mechanical activation may result in poor response to CRT.14
Secondly, additional pathophysiological issues may relate to non-response to CRT. In particular, the presence of extensive scar tissue in the left ventricle may hamper response to CRT.15 If substantial scar tissue is present where the left ventricular pacing lead is located, response to CRT will be minimal.15 Moreover, not only the location but also the extent of scar tissue in the entire left ventricle is important, for response to CRT. It has been shown that patients with extensive scar tissue (irrespective of the location) have a low likelihood of response to CRT.16 Accordingly, the clinician needs information on the presence and location of scar tissue, and this information can be provided by various imaging techniques, including echocardiography, magnetic resonance imaging, and nuclear cardiology.
In addition, the presence of severe right ventricular dysfunction and high pulmonary artery pressures may be related to lack of response to CRT. This information can be provided by echocardiography. Finally, in some patients, it may be useful to obtain information on the presence and location of cardiac veins prior to implantation. If cardiac veins are absent in the region with latest mechanical activation, a transvenous approach for left ventricular pacing lead may not be preferred (since this will result in lead positioning outside the region of latest mechanical activation with poor response to CRT), and a surgical (minimally invasive) approach with epicardial left ventricular lead positioning may be preferred. In this respect, non-invasive visualization of cardiac venous anatomy can be provided by multi-slice computed tomography with high precision.17
Thirdly, adequate programming of the CRT device is needed. The programming of the device has to be tailored for each patient and is obtained by the optimization of AV and interventricular delays. To determine these optimal delays, the clinician needs to have information on the haemodynamic status for each setting. Using echocardiography, the haemodynamic status can be assessed continuously while AV and interventricular delays are changed.10
In summary, what information from imaging techniques does the clinician need in CRT? In the selection process for CRT, the following information is useful. CRT patients are primarily heart failure patients with a poor left ventricular function, and therefore, a robust assessment of systolic and diastolic function is needed; also information on left ventricular filling pressures is useful. Accurate information on LVEF is primarily important since the major AHA/ACC/NASPE and ESC guidelines indicate that LVEF is a major selection criterium for CRT (and intracardiac cardioverter defibrillator). Then, reliable information on cardiac dyssynchrony is needed; although current guidelines at present have not included cardiac dyssynchrony in the selection criteria for CRT, the likelihood of response to CRT is higher in the presence of left ventricular dyssynchrony. Moreover, the site of latest mechanical activation is important for positioning of the left ventricular pacing lead. Subsequently, information on the presence and extent of scar tissue is needed, keeping in mind that patients with extensive scar tissue have a low likelihood of response to CRT and that scar tissue in the preferred left ventricular lead position may result in failure to CRT. Lastly, in some patients, it would be useful to have information on the presence and extent of cardiac veins, which may help to determine the implantation strategy (transvenous vs. surgical epicardial left ventricular lead implantation). It also becomes evident that not only the individual pieces of information described above will be important to obtain, but also the integration of this information, and fusion of imaging modalities will be needed. For example, the information on the sites of latest mechanical information from 3D tissue Doppler imaging has been integrated with MSCT information on the cardiac veins.17
Finally, after CRT implantation, information to guide optimal AV and interventricular delays is needed, and this can be derived from echocardiography.
Conflict of interest: none declared.
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[1] The Task Force for Cardiac Pacing and Cardiac Resynchronization Therapy of the European Society of Cardiology. Guidelines for cardiac pacing and cardiac resynchronization therapy. Eur Heart J (2007) 28:2256–95.
[2] Leclercq C, Kass DA. Retiming the failing heart: principles and current clinical status of cardiac resynchronization. J Am Coll Cardiol (2002) 39:194–201.
[3] Cazeau S, Leclercq C, Lavergne T, Walker S, Varma C, Linde C, et al. Effects of multisite biventricular pacing in patients with heart failure and intraventricular conduction delay. N Eng J Med (2001) 344:873–80.
[4] Cleland JGF, Daubert C, Erdmann E, Freemantle N, Gras D, Kappenberger L, et al, Cardiac Resynchronization-Heart Failure (CARE-HF) Study Investigators. The effect of cardiac resynchronization therapy on morbidity and mortality in heart failure (the CArdiac REsynchronization-Heart Failure [CARE-HF] Trial). N Eng J Med (2005) 352:1539–49.
[5] Bader H, Garrigue S, Lafitte S, Reuter S, Jais P, Haissaguerre M, et al. Intra-left ventricular electromechanical asynchrony: a new independent predictor of severe cardiac events in heart failure patients. J Am Coll Cardiol (2004) 43:248–56.
[6] Leclercq C, Faris O, Tunin R, Johnson J, Kato R, Evans F, et al. Systolic improvement and mechanical resynchronization does not require electrical synchrony in the dilated failing heart with left bundle-branch block. Circulation (2002) 106:1760–3.
[7] Yu CM, Linh H, Zangh Q. High prevalence of left ventricular systolic and diastolic asynchrony in patients with congestive heart failure and normal QRS duration. Heart (2003) 89:54–60.
[8] Hawkins N, Petrie M, MacDonald M, Hogg K, McMurray J. Selecting patients for cardiac resynchronization therapy: electrical or mechanical dyssynchrony? Eur Heart J (2006) 27:1270–1281.
[9] Cazeau S, Gras D, Lazarus A, Ritter P, Mugica J. Multisite stimulation for correction of cardiac asynchrony. Heart (2000) 84:579–81.
[10] Gorcsan J 3rd, Abraham T, Agler DA, Bax JJ, Derumeaux G, Grimm RA, et al, Echocardiography for cardiac resynchronization therapy: recommendations for performance and reporting—a report from the American Society of Echocardiography Dyssynchrony Writing Group endorsed by the Heart Rhythm Society. American Society of Echocardiography Dyssynchrony Writing Group. J Am Soc Echocardiogr (2008) 21:191–213.[CrossRef][Web of Science][Medline]
[11] Chung E, Leon A, Tavazzi L, Sun JP, Nihoyannopoulos P, Merlino J, et al. Results of the Predictors of Response to CRT (PROSPECT) Trial. Circulation (2008) 117:2608–16.
[12] Westenberg JJ, Lamb HJ, van der Geest RJ, Bleeker GB, Holman ER, Schalij MJ, et al. Assessment of left ventricular dyssynchrony in patients with conduction delay and idiopathic dilated cardiomyopathy: head-to-head comparison between tissue Doppler imaging and velocity-encoded magnetic resonance imaging. J Am Coll Cardiol (2006) 47:2042–8.
[13] Henneman MM, Van der Wall EE, Ypenburg C, Bleeker GB, Van de Veire NR, Marsan NA, et al. Nuclear imaging in cardiac resynchronization therapy. J Nucl Med (2007) 48:2001–10.
[14] Leclercq C, Importance of concordance between left ventricular pacing sites and latest activated regions. Myth or reality? Heart (2007) 94:1170–2.
[15] Bleeker G, Kaandorp A, Lamb H, Boersma E, Steendijk P, de Roos A, et al. Effect of postero-lateral scar tissue on clinical and echocardiographic improvement after cardiac resynchronization therapy. Circulation (2006) 113:969–76.
[16] Ypenburg C, Roes SD, Bleeker GB, Kaandorp TA, De Roos A, Schalij MJ, et al. Effect of total scar burden on contrast-enhanced magnetic resonance imaging on response to cardiac resynchronization therapy. Am J Cardiol (2007) 99:657–60.[CrossRef][Web of Science][Medline]
[17] Van de Veire NR, Marsan NA, Schuijf CD, Bleeker GB, Wijffels MC, van Ervan L, et al. Noninvasive imaging of cardiac venous anatomy with 64-slice multi-slice computed tomography and noninvasive assessment of left ventricular dyssynchrony by 3-dimensional tissue synchronization imaging in patients with heart failure scheduled for cardiac resynchronization therapy. Am J Cardiol (2008) 101:1023–9.[CrossRef][Web of Science][Medline]
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