Europace Advance Access published online on January 11, 2007
Europace, doi:10.1093/europace/eul149
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Spectral pulsed-wave tissue Doppler imaging lateral-to-septal delay fails to predict clinical or echocardiographic outcome after cardiac resynchronization therapy
Department of Cardiology, Thoraxcenter, Erasmus Medical Center Rotterdam, Dr Molewaterplein 40, 3015 GD, Room Ba304, Rotterdam, The Netherlands
Manuscript submitted 25 July 2006. Accepted after revision 3 October 2006.
* Corresponding author. Tel: +31 10 4635669; fax: +31 10 4635498. E-mail address: f.j.tencate{at}erasmusmc.nl
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Abstract |
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Aims The current study sought to assess if pre-implantation lateral-to-septal delay (LSD)
60 ms assessed by spectral pulsed-wave myocardial tissue Doppler imaging (PW-TDI) could predict successful long-term outcome after cardiac resynchronization therapy (CRT).
Methods and results Sixty patients (72% males, mean age 59±10 years) who were referred for CRT according to the ACC/ESC guidelines were enrolled in the study. All patients underwent spectral PW-TDI before and 1 year after CRT. Two left ventricular (LV) dyssynchrony time intervals, TO and TP (time to onset and peak of LV myocardial velocity, respectively), LSD were recorded. Left ventricular dyssynchrony was defined as LSD 60 ms. Clinical response was defined as an improvement in >1 NYHA class plus improvement in 6-min walk distance (6MWD) 25%, echocardiographic response was defined as a 15% reduction in LV end-systolic volume (LV-ESV). One year after CRT, 50 patients (83%) were clinical responders and 47 patients (78%) were echocardiographic responders. Both TO and TP LV dyssynchrony indices failed to predict echocardiographic CRT outcome. In addition, there were no significant differences between ‘synchronous’ and ‘dyssynchronous’ patient populations at baseline or follow-up in either clinical (NYHA class and 6MWD) or echocardiographic (LV ejection fraction, LV end-diastolic, and end-systolic) variables.
Conclusion The great majority of patients referred for CRT benefit clinically from it. However, spectral PW-TDI failed to predict CRT outcome. When PW-TDI dyssynchrony was applied for selection of proper CRT patients, up to 80–86% of the patients with synchronous LSD that had proven clinical and echocardiographic benefit from CRT would have been denied CRT.
Key Words: Cardiac resynchronization therapy, Myocardial tissue Doppler imaging, Mechanical dyssynchrony
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Introduction |
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Cardiac resynchronization therapy (CRT) with biventricular pacing improves functional status and cardiac function in patients with the triad of severe systolic dysfunction, wide QRS complex, and symptomatic heart failure.1
,2 However, approximately one-third of patients are either echocardiographic or clinical non-responders to CRT.3 Baseline left ventricular (LV) dyssynchrony assessed by tissue Doppler imaging (TDI) has been shown to predict responders to CRT.4 However, most of these studies have been done with colour-coded Doppler TDI,4–7 whereas in everyday practice most clinicians use spectral pulsed-wave (PW)-TDI to assess LV dyssynchrony. Unfortunately, studies using spectral PW-TDI are limited and not uniform in presentation.6,8–12 Therefore, we investigated the role of spectral PW-TDI in the proper selection of our CRT candidates. |
Methods |
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Study population
Sixty-nine consecutive heart failure patients referred for CRT were enrolled into the study according to the following criteria: (i) New York Heart Association (NYHA) functional class
III despite optimal drug therapy, (ii) impaired LV ejection fraction [(LV-EF) <35%], and (iii) wide QRS complex >120 ms. These CRT indications comply with current guidelines.13,14 Patients with acute coronary syndromes or coronary revascularization within 6 months before CRT were excluded. At baseline and 1 year after CRT implantation all patients underwent a standard two-dimensional echocardiographic examination, including PW-TDI of the LV lateral and septal walls7,15 and clinical assessment, including a NYHA class assessment and 6-min walk distance (6MWD) testing.16,17
Echocardiography
All patients were examined using a Sonos 7500 ultrasound system (Philips, Best, The Netherlands) in accordance to the guidelines of the American Society of Echocardiography.18 Left ventricular end-diastolic volume (LV-EDV), LV end-systolic volume (LV-ESV), and LV-EF (by modified bi-plane Simpson rule) were calculated from the apical four-chamber and two-chamber views.
Pulsed-wave tissue Doppler imaging
In brief, spectral PW-TDI was applied by placing the sample volume in the middle of the basal portions of the LV septal and lateral walls in an apical four-chamber view. Gain and filter settings were adjusted as needed to eliminate background noise and to allow for a clear tissue signal. Pulsed-wave tissue Doppler imaging velocities were recorded end-expiratory at a sweep speed of 100 mm/s and measured using electronic calipers with EnConcert software (Philips). The myocardial velocity waves were defined by three positive waves: S1 (the first wave representing the isovolumic contraction phase), S2 (after S1, during mechanical systole), and S3 (during isovolumic relaxation phase). As shown in Figure 1, two time intervals, linked to the start of the QRS complex were recorded: TO (time-to-onset of S2) and TP (time-to-peak of S2).7,15 These time intervals were rounded to the nearest 5 ms. Each parameter was measured and averaged over three consecutive beats during sinus rhythm and over five consecutive beats for non-sinus rhythm. Left ventricular dyssynchrony was defined as a lateral-to-septal delay (LSD) 60 ms, in accordance with the published data from colour TDI.7,19 Three highly experienced sonographers performed all echocardiograms. All TDI time intervals were measured by one single observer (OIIS). For testing reproducibility of TDI time intervals, a second observer (AMA) who was blinded to the patient's data performed the measurements again on the same data in all patients.
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Device implantation
The CRT device-implanting electrophysiologist was blinded to the measured TO and TP results. Device implantation was performed preferably with a single left pectoral incision, a left cephalic vein cutdown, and a left subclavian puncture. The defibrillation lead was positioned in the right ventricular apex. The left ventricular pacing lead was placed in a tributary of the coronary sinus. A postero-lateral branch was used in 39 patients (65%), a lateral branch in 8 patients (13%), and an antero-lateral branch in 13 patients (22%). Adequate pacing and sensing properties of all leads were tested. All implanted biventricular pacing devices were combined with an internal cardioverter-defibrillator. The lowest effective defibrillation energy was assessed in all patients or a safety margin
10 J was documented. The implanted devices were InSync 7272, 7279, and 7298 (Medtronic Inc, Minneapolis, MN, USA), Renewal II (Guidant Inc, St Paul, MN, USA), and Epic HF V-339 and Atlas HF V-341 (St Jude Medical, Sylmar, CA, USA). For all patients, ICD programming was intended to avoid inappropriate therapy and tailored according to the clinical presentation. The atrioventricular delay was optimized by two-dimensional echocardiography to provide the longest filling time for completion of the end-diastolic filling flow before left ventricular contraction.
Definition of responders
A patient was considered a clinical responder when at least reduction of 1 NYHA class plus an improvement of 25% increase in the 6MWD12 was noted and an echocardiographic responder when a 15% reduction in LV-ESV was noted.
Statistical analysis
Data were expressed as mean±SD; independent and paired-sample t tests were used when appropriate. An alpha level of significance <0.05 was considered significant. All statistics were performed using SPSS (12.0.2) for Windows (Chicago, IL, USA). Bland-Altman method of comparison was used to assess inter-observer variability.20
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Results |
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Transvenous implantation of the CRT device was successful in 66 patients (96%), in the remaining three patients the LV lead was surgically implanted. During follow-up, one patient died (due to heart failure exacerbation) at 6 months and three patients underwent heart transplantation. In five patients, PW-TDI measurements could not be performed due to inability to define accurately the systolic S2 wave. These nine patients were excluded from further analysis. So, at 1 year 60 patients (mean age 59±10 years, 43 males) were considered for analysis of which 50 patients (83%) were clinical responders and 47 patients (78%) were echocardiographic responders. As seen in Table 1, echocardiographic responders had a significantly greater baseline clinical and echocardiographic characteristics. During follow-up, echocardiographic responders and non-responders had comparable improvement in 6MWD testing.
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Relation of pre-implantation PW-TDI to CRT response
As shown in Table 1 and Figure 2, in the total population CRT significantly reduced the LSD-TO from 76±44 to 30±24 ms (P<0.001), and LSD-TP from 80±47 to 40±32 ms (P<0.001). In the echocardiographic responders, LSD-TO reduced from 78±48 to 25±18 ms and LSD-TP reduced from 81±48 to 33±27 ms (both P<0.0001). Less changes were found in the echocardiographic non-responders, in whom LSD-TO reduced from 65±24 to 49±33 ms, and LSD-TP reduced from 78±48 to 67±32 ms (both P<0.0001). The study population was classified according to the baseline (pre-CRT) 60 ms LSD cut-off value into synchronous patients (LSD <60 ms) and dyssynchronous patients (LSD
60 ms). As seen in Table 2, for both TO and TP assessments there were no significant differences in baseline to follow-up changes in NYHA class, 6MWD testing, LV-EDV, LV-ESV, and LV-EF for patients with and without LV dyssynchrony. Eighteen patients (86%) with LSD-TP <60 ms and 16 patients (80%) with LSD-TO <60 ms were echocardiographic responders. Likewise 19 patients (90%) with LSD-TP <60 ms and 17 patients (85%) with LSD-TO <60 ms were clinical responders (Table 2).
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Reproducibility of TDI measurements
There was a fair interobserver agreement for baseline TO (mean difference=–1.2±5.5 ms, 95% limits of agreement=–11.9, 9.6), and TP (mean difference=–0.3±5.6 ms, 95% limits of agreement=–11.4, 10.9). Likewise, there was a good interobserver agreement for follow-up TO (mean difference=0.3±6.1 ms, 95% limits of agreement=–11.9, 12.4) and TP (mean difference=–0.2±4.5 ms, 95% limits of agreement=–9.2, 8.9).
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Discussion |
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In the present study, 60 patients with severe heart failure, impaired LV ejection fraction, and a wide QRS complex underwent CRT according to the current guidelines.13
,14 All patients were assessed with spectral PW-TDI before and 1 year after CRT. One year after CRT, 50 patients (83%) were clinical responders (reduction of 1 NYHA class plus an improvement of 25% increase in the 6MWD) and 47 patients (78%) were echocardiographic responders (15% reduction in LV-ESV) (Figure 3). Baseline (pre-CRT) LV dyssynchrony was assessed with spectral PW-TDI and defined as a LSD 60 ms.8,15 The main finding of our study is that both LSD-TO (time delay to onset of mechanical LV contraction) and LSD-TP (time delay to peak of mechanical LV contraction) could not predict changes in functional class, 6MWD testing, LV-EDV, LV-ESV, and LV-EF. Actually, if CRT therapy had only been offered to patients with LV dyssynchrony, 18 patients (86%) with synchronous LSD-TP and 16 patients (80%) with synchronous LSD-TO that demonstrated reverse remodelling and likewise 19 patients (90%) with synchronous LSD-TP and 17 patients (85%) with synchronous LSD-TO who clinically benefited from CRT would have been denied CRT.
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Reasons for use of spectral PW-TDI in the current study
At present time, evaluation of myocardial tissue velocity can be achieved by either spectral PW-TDI or colour-coded TDI. Spectral PW-TDI has a high temporal resolution of 3–4 ms (250–333 frames per second) and relatively low spatial resolution, whereas colour-coded TDI has a somewhat lower temporal resolution of 6–10 ms (100–166 frames per second) but higher spatial resolution. Both techniques can assess myocardial velocity and timing of TDI-derived waves of cardiac motion. However, to achieve reproducible data, colour-coded TDI necessitates a high (80–100) frame rate, which is not available in most echocardiographic machines. On the other hand, spectral PW-TDI is widely available in nearly every echocardiography laboratory and can be accurately performed by a fairly experienced sonographer. Previous data suggests that LSD derived from colour-coded TDI can be used for patient selection for CRT.7
In the real world, spectral PW-derived measurements of LSD are often used instead of colour-coded TDI derived measurements for selection of candidates for CRT. Thus, it is necessary to test if these widely available measurements of LSD based on spectral PW-TDI have a predictive value compared with the more established colour-coded TDI measurements.
Reasons for failure of PW-TDI to predict CRT outcome
Despite the fact that spectral PW-TDI is a single-dimensional assessment of myocardial motion, its contribution to the evaluation of regional myocardial velocities has been widely accepted.21 However, in our study PW-TDI failed to predict CRT outcome, which may be explained by many factors. Pulsed-wave myocardial tissue Doppler imaging is prone to angle-related errors and does not allow simultaneous timing of regional myocardial motion in one beat, with each beat affected by differences in loading conditions, heart rate, and respiration. The respiratory factor was minimized in our study by recording the PW-TDI measurements at a stable end-expiratory phase. Beat-to-beat variability may have played an important role in the included patients with atrial fibrillation. Patients with atrial fibrillation were, however, also not excluded in some other studies8,11,22 and exclusion of these patients did not change our results. Another important limitation of PW-TDI is the difficulty in many patients with poor LV function and in particular in patients with ischaemic cardiomyopathy, to identify the peak of mechanical contraction. In our study, five patients with non-interpretable PW-TDI studies (technical failure) were excluded from analysis. As a result, the interobserver agreement of LSD-TP measurements in our study was fair. In addition, because of this known limitation we analysed also LSD-TO. As shown in our study, LV dyssynchrony based on LSD-TO measurements could also not predict outcome after CRT. Another important factor for the negative results in our study may be the inability for PW-TDI LSD measurements to detect mechanical LV dyssynchrony (physiological failure). Left ventricular dyssynchrony is a complex, three-dimensional issue including electromechanical coupling, the pattern of electrical LV activation, the distribution of myocardial fibres, and torsion forces on the cardiac fibres. Although the short time for acquisition and analysis of a two-segment velocity model is very practical, optimal LV dyssynchrony analysis should include at least more segments analysed23 or even a three-dimensional analysis of myocardial velocities and deformation.6,24,25 Moreover, it should be mentioned that even two-dimensional colour-coded TDI measurements based on 12 segments failed to predict CRT outcome in a recent publication from the Mayo clinic26 and correlated less with acute reduction in LV-ESV than strain imaging.27 Finally, it should be noticed that although timing of LV muscle displacement is important, the extent of (miss) timed muscle displacement is not measured by PW-TDI and may be a crucial factor (a small dyssynchronous muscle area may not necessarily have a great impact on LV-EF).
Comparison with previous studies
In the literature, only five series of patients are reported that underwent spectral PW-TDI before CRT.8–11,28 From only one study the predictive value of LSD <60 ms for CRT outcome could be deducted.8 Although in the latter study PW-TDI results were called positive in terms of prediction of clinical CRT outcome, it should be emphasized that actually only three of the studied patients were clinical non-responders. Other studies only concluded that more dyssynchronous patients had a better short-term CRT outcome, without reporting a practical cut-off LSD value.9–11,28 In one of these studies28 only acute haemodynamic changes were reported and such changes do not necessarily reflect reverse remodelling, which needs long-term follow-up. In another study, LV-EF was used to define responders,11 whereas we used a reduction in LV-ESV to define responders because this parameter is known to be more predictive of cardiac events.29 In a recently published series of patients followed up for only 3 months,23 a multi-segment model was superior to a two-segment model as used in our study. The main purpose of our study was to implement a simple and practical technique that may be used for patient selection for CRT. Since the high frame rate needed for colour-coded TDI is not available in every ultrasound machine and analysis of multiple segments is time-consuming, we tested the clinically most practised two-segment spectral PW-TDI model for LSD.
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Conclusions |
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The great majority of patients with current CRT indications benefit clinically from it. However, spectral PW-TDI failed to predict CRT outcome. When PW-TDI dyssynchrony was applied for selection of proper CRT patients, up to 90% of the patients with synchronous LSD that clinically benefited from CRT would have been denied CRT. Further studies using other echocardiographic techniques like three-dimensional regional timing of wall motion are necessary to determine the use of ultrasound for the selection of CRT patients.
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Footnotes |
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Dr Osama I.I. Soliman and Dr Ashraf Anwar are visiting fellows from the Al Azhar University (Cairo, Egypt) and supported by the Egyptian Government. 
Dr Attila Nemes is a visiting fellow from the University of Szeged (Szeged, Hungary) and supported by ‘Research Fellowship of the European Society of Cardiology’.
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