CLINICAL RESEARCH: ARRHYTHMIAS, RIGHT VENTRICULAR FUNCTION, AND MITRAL REGURGITATION
Left Ventricular Dyssynchrony Predicts Right Ventricular Remodeling After Cardiac Resynchronization Therapy
Gabe B. Bleeker, MD*, ,
Martin J. Schalij, MD, PhD*,
Petros Nihoyannopoulos, MD ,
Paul Steendijk, PhD*,
Sander G. Molhoek, MD*,
Lieselot van Erven, MD, PhD*,
Marianne Bootsma, MD, PhD*,
Eduard R. Holman, MD, PhD*,
Ernst E. van der Wall, MD, PhD* and
Jeroen J. Bax, MD, PhD*,*
* Department of Cardiology, Leiden University Medical Center, Leiden, the Netherlands
Interuniversity Cardiology Institute of the Netherlands (ICIN), Utrecht, the Netherlands
Imperial College London, NHLI and Cardiothoracic Directorate, Hammersmith Hospital, London, United Kingdom.
Manuscript received January 4, 2005;
revised manuscript received February 28, 2005,
accepted April 4, 2005.
* Reprint requests and correspondence: Dr. Jeroen J. Bax, Department of Cardiology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, the Netherlands. (Email: jbax{at}knoware.nl).
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Abstract
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OBJECTIVES: The purpose of this research was to evaluate right ventricular (RV) remodeling after six months of cardiac resynchronization therapy (CRT).
BACKGROUND: Cardiac resynchronization therapy is beneficial in patients with end-stage heart failure. The effect of CRT on RV size is currently unknown. Accordingly, the effects of CRT on RV size, severity of tricuspid regurgitation, and pulmonary artery pressure were evaluated.
METHODS: Fifty-six consecutive patients with end-stage heart failure (52% ischemic cardiomyopathy), left ventricular (LV) ejection fraction (EF)  35%, QRS duration >120 ms, and left bundle branch block were included. Clinical parameters, LV volumes, LVEF, LV dyssynchrony, and RV chamber size were assessed at baseline and after six months of CRT; LV dyssynchrony was assessed using tissue Doppler imaging.
RESULTS: Clinical parameters improved significantly; LV dyssynchrony was acutely reduced after CRT and remained unchanged at six-month follow-up. Left ventricular EF improved significantly from 19 ± 6% to 26 ± 8% (p < 0.001), and LV end-diastolic volume decreased from 257 ± 98 ml to 227 ± 86 ml (p < 0.001). Right ventricular annulus decreased significantly from 37 ± 9 mm to 32 ± 10 mm, RV short-axis from 29 ± 11 mm to 26 ± 7 mm, and RV long-axis from 89 ± 11 mm to 82 ± 10 mm (all p < 0.001). Left ventricular and RV reverse remodeling were only observed in patients with substantial LV dyssynchrony at baseline. Finally, significant reductions in severity of tricuspid regurgitation and pulmonary artery pressure were observed.
CONCLUSIONS: Cardiac resynchronization therapy results in significant reverse LV and RV remodeling after six months of CRT in patients with LV dyssynchrony. Moreover, CRT leads to a reduction of the severity of tricuspid regurgitation and a decrease in pulmonary artery pressure.
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Abbreviations and Acronyms
| | CRT = cardiac resynchronization therapy | | LAX = long-axis | | LV = left ventricle/ventricular | | LVEF = left ventricular ejection fraction | | NYHA = New York Heart Association | | RV = right ventricle/ventricular | | SAX = short-axis | | TDI = tissue Doppler imaging | | TV ANN = tricuspid valve annulus |
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Congestive heart failure is one of the leading causes of morbidity and mortality in the Western world (1,2). A relatively new treatment modality in patients with end-stage heart failure and a wide QRS complex is cardiac resynchronization therapy (CRT). Several large randomized trials have shown sustained clinical benefit from CRT (3–7). Patients experienced an improvement in heart failure symptoms, quality-of-life, and exercise capacity. Moreover, CRT results in a significant reduction of the number of hospitalizations for decompensated heart failure, and recent trials indicate a positive effect of CRT on mortality (3–8).
Echocardiographic evaluation of patients undergoing CRT indicated that clinical improvement is caused by resynchronization of dyssynchronous left ventricular (LV) contraction (9–12). The CRT-induced LV resynchronization results in improved LV systolic function, a decrease in mitral regurgitation, and reverse LV remodeling (9–13). Currently, no data are available regarding the effects of CRT on right ventricular (RV) chamber size and the severity of tricuspid regurgitation. Beneficial effects of CRT on the size of the RV and on the severity of tricuspid regurgitation may further explain the mechanism of symptomatic benefit from CRT (14,15).
Accordingly, the objective of this study was to evaluate RV remodeling after six months of CRT using echocardiography. The effects of CRT on the severity of tricuspid regurgitation and pulmonary artery pressure were also evaluated. Finally, the relation between LV dyssynchrony and the effects of CRT on the RV was explored.
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Methods
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Patients and study protocol.
Fifty-six consecutive patients with severe heart failure, scheduled for implantation of a biventricular pacemaker, were prospectively included in this study. Patients were selected according to traditional selection criteria for CRT: left ventricular ejection fraction (LVEF) 35%, severe heart failure (New York Heart Association [NYHA] functional class III or IV), and a QRS duration >120 ms with left bundle branch block configuration. Patients with a recent myocardial infarction (<3 months) or decompensated heart failure were excluded.
Before pacemaker implantation, clinical status and QRS duration were assessed. Two-dimensional echocardiography at rest was performed to calculate LV volumes and LVEF, and to assess RV chamber size. Next, tissue Doppler imaging (TDI) was performed to evaluate LV dyssynchrony. Left ventricular dyssynchrony and QRS duration were reassessed on the day after implantation and at six-month follow-up. Clinical status, LV volumes, LVEF, and RV chamber size were also reassessed at six-month follow-up.
Clinical evaluation.
Evaluation of clinical status included assessment of NYHA functional class, quality-of-life score (using the Minnesota quality-of-life questionnaire), and 6-min hall-walk test. In all patients, QRS duration was measured from the surface electrocardiogram (ECG) using the widest QRS complex from the leads II, V1, and V6. The ECGs were recorded at a speed of 25 mm/s and were evaluated by two independent observers without knowledge of the clinical status of the patient.
Echocardiography.
Resting echocardiography and TDI were performed at baseline, the day after implantation, and at six-month follow-up. Patients were imaged in the left lateral decubitus position using a commercially available system (Vingmed System Seven, General Electric-Vingmed, Milwaukee, Wisconsin). Images were obtained using a 3.5-MHz transducer, at a depth of 16 cm in the parasternal and apical views (standard long-axis [LAX] and two- and four-chamber images). Standard two-dimensional and color Doppler data, triggered to the QRS complex, were saved in cine loop format. Left ventricular volumes (end-systolic, end-diastolic) and LVEF were calculated from the conventional apical two- and four-chamber images, using the biplane Simpson’s technique (16).
Assessment of RV chamber size
Right ventricular end-diastolic chamber size was assessed using three parameters that were described previously by Foale et al. (17,18). These parameters were assessed from the apical four-chamber view, as schematically displayed in Figure 1. The first parameter is the diameter of the tricuspid valve annulus (TV ANN), defined as the point of attachment of the septal and posterior leaflets to the atrioventricular junction. The second measurement is the maximum dimension of the middle third of the RV, parallel to the tricuspid annulus (RV short-axis [SAX]). The last measurement included the major axis of the RV (RV LAX) and is defined as the distance between the RV apex to the mid-point of the tricuspid annulus.
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Figure 1 Apical four-chamber two-dimensional echocardiogram. Schematic display of parameters reflecting right ventricular (RV) end-diastolic chamber size. LAX = long-axis; SAX = short-axis; TV ANN = tricuspid valve annulus.
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Inter- and intraobserver agreement for assessment of RV chamber size were 98% and 96% for TV ANN, 90 and 92% for RV SAX, and 94% and 95% for RV LAX, respectively.
TDI to assess LV dyssynchrony
In addition to the conventional echocardiographic examination, TDI was performed to assess LV dyssynchrony. For TDI, color Doppler frame rates varied between 80 and 115 frames/ s depending on the sector width of the range of interest; pulse repetition frequencies were between 500 Hz and 1 KHz, resulting in aliasing velocities between 16 and 32 cm/s. Tissue Doppler imaging parameters were measured from color images of three consecutive heart beats by offline analysis. Data were analyzed using commercial software (Echopac 6.1, General Electric-Vingmed).
To determine LV dyssynchrony, the sample volume was placed in the basal portions of the septum and the LV lateral wall; peak systolic velocities and time-to-peak systolic velocities were obtained, and the delay in peak velocity between the septum and the LV lateral wall was calculated as an indicator of LV dyssynchrony (referred to as the septal-to-lateral delay) (9,19,20). Interventricular dyssynchrony was assessed by comparing the delay between peak systolic velocity of the RV free wall and the LV lateral wall (11).
Based on previous observations, a septal-to-lateral delay >60 ms was considered to represent severe LV dyssynchrony (9). Inter- and intraobserver agreement for assessment of the septal-to-lateral delay were 90% and 96%, respectively (21).
Assessment of mitral and tricuspid regurgitation
The severity of mitral and tricuspid regurgitation was graded semiquantitatively from color-flow Doppler images. For quantification of mitral and tricuspid regurgitation, the apical four-chamber images were used. Mitral and tricuspid regurgitation were classified as: mild = 1+ (jet area/atrial area <10%), moderate = 2+ (jet area/atrial area 10% to 20%), moderately severe = 3+ (jet area/atrial area 20% to 45%), and severe = 4+ (jet area/atrial area >45%) (22,23).
Continuous-wave Doppler examination was also performed to estimate pulmonary artery systolic pressure from the transtricuspid maximal regurgitant flow velocity.
All echocardiographic measurements were obtained by two independent observers without knowledge of the clinical status of the patient.
Pacemaker implantation.
The LV pacing lead was inserted transvenously via the subclavian route. First, a coronary sinus venogram was obtained during occlusion of the coronary sinus using a balloon catheter. Next, the LV pacing lead was inserted in the coronary sinus with the help of an 8-F guiding catheter and positioned as far as possible in the venous system, preferably in the (postero)lateral vein. The right atrial and RV leads were positioned conventionally. When a conventional indication for an internal defibrillator existed, a combined device was implanted. For each patient the atrioventricular interval was adjusted to maximize the mitral inflow duration using pulsed-wave Doppler echocardiography. No adjustments were made to the V-V interval during the first six months of CRT.
Cardiac resynchronization therapy device and lead implantation was successful in all patients without major complications (Contak TR or CD, Guidant Corp., Minneapolis, Minnesota, and Insync III or CD, Medtronic Inc., Minneapolis, Minnesota). Two types of LV leads were used (Easytrack 4512 to 80, Guidant Corp., or Attain-SD 4189, Medtronic Inc.).
Statistical analysis.
Continuous data were expressed as mean values ± SD and compared with the two-tailed Student t test for paired and unpaired data when appropriate. Univariate analysis for categorical variables was performed using the chi-square test with Yates’ correction. For all tests a p value <0.05 was considered statistically significant.
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Results
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Fifty-six consecutive patients were included in this study (44 men, age 64 ± 11 years). Baseline patient characteristics are summarized in Table 1.
Follow-up after CRT.
Clinical parameters and LV remodeling
QRS duration at baseline was 176 ± 30 ms (range 122 to 240 ms) and shortened to 149 ± 23 ms (p < 0.001, range 92 to 198 ms) immediately after implantation, which remained unchanged (153 ± 22 ms, range 86 to 202 ms) at six months after CRT.
At six-month follow-up, a significant improvement in clinical status was observed, in combination with an improvement in LVEF and a significant LV reverse remodeling (Table 2).
LV dyssynchrony
The day after implantation of the pacemaker, TDI demonstrated a significant reduction in septal-to-lateral delay from 114 ± 57 ms to 37 ± 32 ms (p < 0.001), indicating LV resynchronization. Resynchronization was maintained after six months of CRT, as evidenced by a septal-to-lateral delay of 40 ± 36 ms (p < 0.001 vs. baseline, p = NS vs. immediately after implantation). Mean interventricular (RV-LV) dyssynchrony at baseline was 51 ± 36 ms, which decreased significantly after six months of CRT to 37 ± 27 ms (p < 0.05).
RV remodeling
In line with the reverse remodeling of the LV, CRT also resulted in a significant reverse remodeling of the RV at six-month follow-up (Table 2). All three parameters reflecting RV chamber size showed a significant decrease after six months of CRT. The TV ANN showed a significant decrease from 37 ± 9 mm to 32 ± 10 mm (p < 0.01), RV SAX decreased from 29 ± 11 mm to 26 ± 7 mm (p < 0.001), and RV LAX showed a reduction from 89 ± 11 mm to 82 ± 10 mm (p < 0.001). Of note, RV reverse remodeling did not occur immediately after CRT (e.g., the RV SAX was 29 ± 11 mm before CRT and 30 ± 10 mm immediately after CRT, p = NS).
Patients were subsequently divided into quartiles according to the baseline values for each RV size parameter. Right ventricular reverse remodeling was most outspoken in patients with the largest RV dilation at baseline (Figs. 2A to 2C). A significant reduction in TV ANN was demonstrated in the third and fourth quartiles, whereas the patients with smaller TV ANN at baseline (first and second quartiles) showed no significant reduction in size (Fig. 2A). Similarly, RV SAX and RV LAX showed a significant reduction after six months of CRT in patients with larger baseline values (Figs. 2B and 2C). Of note, 6 of 14 patients in the fourth quartile had signs of right-sided heart failure.
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Figure 2 (A) Tricuspid valve annulus (TV ANN) at baseline and after six months of cardiac resynchronization therapy (CRT). Patients are divided into quartiles according to baseline TV ANN. (B) Right ventricular (RV) short-axis (SAX) at baseline and after six months of CRT. Patients are divided into quartiles according to baseline RV SAX. (C) Right ventricular long-axis (LAX) at baseline and after six months of CRT. Patients are divided into quartiles according to baseline RV LAX. Open bars = baseline; solid bars = six-month follow-up. *p < 0.05.
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Right ventricular reverse remodeling was associated with a significant reduction in tricuspid regurgitation from 1.8 ± 0.8 to 1.3 ± 1.0 (p < 0.001; Table 2). Moreover, CRT also resulted in a significant reduction of pulmonary artery pressure from 40 ± 12 mm Hg to 30 ± 11 mm Hg (p < 0.001).
Reverse remodeling versus LV dyssynchrony.
Patients with severe baseline LV dyssynchrony were defined as having a septal-to-lateral delay >60 ms on TDI before implantation of the pacemaker. Accordingly, 44 (79%) patients had significant LV dyssynchrony (mean septal-to-lateral delay 137 ± 41 ms, with an immediate decrease to 40 ± 40 ms after CRT, p < 0.001), and 12 (19%) patients did not have substantial dyssynchrony on TDI (mean septal-to-lateral delay 41 ± 27 ms, which remained unchanged after CRT, 38 ± 25 ms, p = NS). Baseline characteristics were not statistically different between the two groups (Table 3).
The changes in LV volumes, LVEF, and RV diameters in patients with and without LV dyssynchrony are summarized in Table 4. Patients with severe LV dyssynchrony before implantation showed reverse LV remodeling, whereas LV volumes did not decrease significantly after six months of CRT in patients without LV dyssynchrony at baseline. Moreover, LVEF increased significantly after six months of CRT in the patients with LV dyssynchrony only. Similarly, a significant reduction in RV dimensions was observed only in the patients with LV dyssynchrony at baseline.
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Table 4. LV Volumes, LV Ejection Fraction, and RV Dimensions at Baseline and After Six Months of CRT in Patients With (n = 44) and Without LV Dyssynchrony (n = 12) at Baseline
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Of note, in the patients with significant LV dyssynchrony at baseline, 86% showed an improvement of at least one NYHA functional class after six months of CRT.
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Discussion
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The main findings can be summarized as follows. In patients with LV dyssynchrony, CRT induces not only LV reverse remodeling, but also a significant reverse remodeling of the RV. This effect was most outspoken in patients with severe RV dilatation at baseline.
At present, CRT is considered a major breakthrough in the treatment of patients with moderate-to-severe heart failure and has been demonstrated to result in a sustained improvement in symptoms and LV systolic function (5,13). Similar benefits were demonstrated in the current study. Despite the reproducible positive clinical results, the exact mechanism underlying the benefit of CRT is still not entirely clear but may be related to: 1) an improvement of LV systolic function; 2) reduction of mitral regurgitation; and 3) reverse remodeling of the LV. The presence of LV dyssynchrony appears mandatory for these effects to occur as demonstrated in previous studies (9–11,13). In the present study, LV dyssynchrony (assessed by TDI before CRT) was significant with a septal-to-lateral delay of 114 ± 57 ms. In particular, 79% of patients exhibited significant LV dyssynchrony (defined as a septal-to-lateral delay >60 ms), and 21% of patients did not show LV dyssynchrony. In the patients with LV dyssynchrony, resynchronization was obtained immediately after CRT, which persisted during six-month follow-up. A significant improvement in LVEF was observed in the dyssynchronous patients with significant reverse LV remodeling, in line with previous studies (9,11,12). However, these beneficial effects were not observed in the absence of dyssynchrony at baseline (Table 4), confirming previous observations (9,11).
No data were yet available regarding the effects of CRT on RV function. Because CRT causes an improvement in LV function, reduces mitral regurgitation, and normalizes neurohormonal status, it seems plausible that CRT may also have beneficial effects on pulmonary artery pressure, RV function, and RV dilation. In the current study, the effects of CRT on RV size, tricuspid regurgitation, and pulmonary artery pressure were evaluated. Right ventricular chamber size was evaluated using three echocardiographic measurements that were introduced previously by Foale et al. (17,18). This standardized echocardiographic approach for the assessment of RV dimensions has been demonstrated to adequately reflect RV size. The current results illustrate that CRT not only induced LV reverse remodeling, but also resulted in a significant reverse remodeling of the RV. Of interest, the effect was most outspoken in patients with more severe RV dilation at baseline. Moreover, RV reverse remodeling was associated with a reduction in the severity of tricuspid regurgitation and a significant decrease in pulmonary artery pressure. The precise mechanism underlying the beneficial effects on the RV is unclear. Similar to LV reverse remodeling, RV reverse remodeling was related to the presence of LV dyssynchrony at baseline. Patients without baseline LV dyssynchrony did not exhibit RV reverse remodeling after six months of CRT (Table 4). Still, the reduction in RV dimensions appears not related by an acute recovery in LV dyssynchrony. An acute reduction in septal-to-lateral delay occurred after initiation of CRT (from 114 ± 57 ms at baseline to 37 ± 32 ms immediately after CRT, p < 0.01), but this reduction was not accompanied by an acute reduction in RV dimensions (the baseline RV SAX was 29 ± 11 mm as compared to 30 ± 10 mm immediately after CRT). It thus appears that a more coordinated motion of the interventricular septum after CRT was not responsible for the reduction in RV dimensions. Possibly sustained improved LV performance has led to a reduction in pulmonary artery pressure (observed in the current study), resulting in an improved RV function (as evidenced also by a reduction in tricuspid regurgitation). Although improvement in RV size and function after CRT have been demonstrated in the current study, the inclusion of a control group could potentially have contributed to a better understanding of the mechanism involved. Future studies are needed to further resolve these issues.
Conclusions.
The clinical benefit of CRT on improvement in LV function was confirmed in the current study. The benefit from CRT was related to the presence of LV dyssynchrony before CRT. In addition, this is the first study to demonstrate reverse RV remodeling after CRT, which was associated with a reduction in tricuspid regurgitation and a decrease in pulmonary artery pressure; reverse RV remodeling was most outspoken in severely dilated RVs and only observed when LV dyssynchrony was present at baseline. These findings may lead to a better understanding of the beneficial effects of CRT on cardiac function as RV reverse remodeling, decreased tricuspid regurgitation, and reduced pulmonary artery pressure are likely to contribute to the symptomatic benefit from CRT in patients with drug-refractory heart failure.
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Footnotes
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Dr. Bleeker is supported by the Dutch Heart Foundation, grant 2002B109. Dr. Molhoek is supported by the Dutch Heart Foundation, grant 2001D015.
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References
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Abstract
Methods