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Ann Thorac Surg 2007;83:1356-1360
© 2007 The Society of Thoracic Surgeons
a Department of Cardiovascular Surgery, Hokkaido University Hospital, Sapporo, Hokkaido, Japan
b Department of Medical Technology, Hokkaido University School of Medicine, Sapporo, Hokkaido, Japan
Accepted for publication October 27, 2006.
* Address correspondence to Dr Shingu, 1-28-706, Nishi 3 chome, Kita 18 jo, Kitaku, Sapporo, Hokkaido 001-0018, Japan (Email: fwpc1650{at}mb.infoweb.ne.jp).
| Abstract |
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Methods: Twelve patients (mean age, 61 ± 12 years) with chronic type B aortic dissection were enrolled in this study. Patients in group I had double-barrel aortic dissection that had expanded the patent false lumen and narrowed the true lumen (n = 7, 58.3%), and patients in group II had a wider-caliber true lumen with a thrombosed false lumen (n = 5, 41.7%). We evaluated the left ventricular diastolic function with the transmitral flow pattern (E and A waves) with the pulsed Doppler method and flow propagation velocity (FPV) with color M-mode Doppler images, and classified its severity into grade I (abnormal relaxation), grade II (pseudonormalization) and grade III (restriction).
Results: All patients in group II had grade I diastolic dysfunction, with an E/A of less than 1.0. By contrast, 4 of the 7 patients in group I had grade II diastolic dysfunction, with an FPV/E of less than 0.6 and a pseudonormalized (> 1.0) E/A ratio (p = 0.081). Consequently, the E/A ratio was higher in group I than in group II (1.16 ± 0.39 versus 0.68 ± 0.18; p < 0.05).
Conclusions: It is suggested that left ventricular diastolic function is severely reduced in the patients having aortic dissection with a double-barrel and narrowed true lumen.
| Introduction |
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| Material and Methods |
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The study population was divided into two groups. Patients in group I had double-barrel aortic dissection with an enlarged patent false lumen and narrowed true lumen (n = 7, 58.3%), whereas those in group II had a wider-caliber true lumen with a thrombosed false lumen (n = 5, 41.7%). Operative indication was aneurysmal dilatation in all cases, and patients with rupture or ischemic complications related to dissection were not included. Use of the clinical records for research was approved by the Institutional Ethics Review Board. Our committee waived the need for patient consent.
Echocardiography and Doppler Studies
Echocardiographic studies were performed a few days before operations in all cases using a SONOS 5500 ultrasound system (Phillips Medical Systems, Tokyo, Japan) with a 3S transducer (3 to 5 MHz), a Vivid Seven system (GE/Vingmed, Milwaukee, Wisconsin) with an M3S (2.5 to 3.5 MHz) transducer, or an Aplio system (Toshiba Medical Systems, Tokyo, Japan) with a 2.5-MHz transducer by experienced examiners. The following basic variables were measured from parasternal long-axis and short-axis views: LV end-diastolic and end-systolic dimensions (mm); the ejection fraction (%) by the Teichholz method; the left atrial dimension (mm); the interventricular septal thickness; and the LV posterior wall thickness (mm) [5]. The LV mass index, estimated by LV cavity dimension and wall thickness at end-diastole, was also calculated according to the report by Devereux and colleagues [6].
On an apical long-axis color Doppler flow image, a sample pulsed-Doppler volume was located at the tip of the mitral valve leaflets to obtain the transmitral flow velocity. Peak early and late transmitral flow velocities (E and A, respectively [cm/s]), the ratio of early to late peak velocities (E/A), and deceleration time (DT [ms]) of early transmitral flow velocity were measured. Furthermore, isovolumic relaxation time (IRT [ms]) was measured as the period from the end of aortic flow to the onset of mitral inflow using continuous-wave Doppler echocardiography from the same echo window.
A color M-mode Doppler image of LV filling flow in early diastole was also recorded using the apical approach. The ultrasound beam was interrogated from the apex of the heart toward the center of the mitral orifice as close to parallel as possible to the filling flow. The propagation velocity of early diastolic flow (FPV [cm/s]) was measured as the slope of the peak velocity of early diastolic filling flow on the color M-mode Doppler image, as we reported previously [7, 8]. The FPV/E ratio was also calculated to correct the influence of preload on FPV [7]. Five different cardiac cycles were analyzed, and mean values were used for each measurement.
The severity of diastolic dysfunction was classified into three grades, based on the report by Nishimura and colleagues [9]. Grade I diastolic dysfunction (abnormal relaxation) was defined as an E/A ratio of less than 1.0 with prolonged IRT (> 90) and DT (> 240). In grade II diastolic dysfunction, increased filling pressure results in pseudonormalization of the E/A ratio (> 1.0). In this setting, IRT and DT may also be pseudonormalized. Patients with grade III diastolic dysfunction have a restrictive filling pattern on the mitral flow. The E/A ratio becomes more than 2.0 [5, 9, 10]. The FPV/E decreases parallel to the progression of diastolic dysfunction [11]. Significant LV relaxation abnormality (grade I or more) was considered to be present when FPV was less than 50 cm/s or FPV/E was less than 0.6 (Fig 1) [1114].
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Statistical Analysis
All the descriptive data are given as mean ± SD. Statistical analysis was performed with the SPSS version 10.0 software (SPSS, Chicago, Illinois). The Student t test was used for comparing the continuous variables, and the
2 test or Fishers exact test was used to compare frequencies between the groups. A p value of less than 0.05 was considered statistically significant.
| Results |
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The short-axis minimum dimension of the true lumen calculated by computed tomography scanning at the level of the right pulmonary artery was 10.7 ± 2.1 mm and 37.6 ± 9.3 mm in group I and group II, respectively (p = 0.002).
The preoperative antihypertensive medications were also similar and the systolic and diastolic blood pressures were not significantly different. The ankle brachial pressure index was normal in both groups (Table 1).
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Operative Results
The perioperative and postoperative data are shown in Table 4. Thoracoabdominal aortic replacement was performed in 4 patients (33.4%), descending aortic replacement in 4 (33.3%), and arch replacement with or without a frozen elephant trunk in 4 (33.4%). There was no hospital mortality.
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| Comment |
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Echocardiographic Evaluation
Pulsed Dopper measurement of transmitral flow such as DT, IRT, and E/A has been widely used to assess the left ventricular relaxation abnormality. However, pulsed Doppler-derived indexes are affected by several factors, such as alterations of loading conditions. The abnormality of left ventricular relaxation is concealed in patients with more severe diastolic dysfunction because the transmitral flow pattern is pseudonormalized by an increased atrioventricular pressure gradient (grade II). In these patients, pulsed Doppler-derived indexes show poor correlations with invasive variables of left ventricular diastolic properties [7]. Recently, FPV measured by color M-mode Doppler echocardiography has been used as an index of ventricular relaxation [7, 12, 13]. The FPV strongly correlates with left ventricular peak negative dP/dt and minimal pressure. Furthermore, the ratio of component velocity E over the FPV during early filling, by correcting for the effect of left ventricular relaxation, provides a better estimate of pulmonary wedge pressure or left ventricular end-diastolic pressure than does standard transmitral Doppler flow properties. In this study, we evaluated the FPV and FPV/E to differentiate grade II diastolic dysfunction from the normal relaxation pattern. Because we routinely use the FPV/E, but not the E/FPV based on the clinical experience, we applied the former in this study [7].
Aortic Morphology
We divided the study population into two groups according to the presence of a patent false lumen. In the double-barrel aorta, the true lumen is compressed by an expanded false lumen. Therefore, we hypothesized that the left ventricular afterload is higher in group I than group II, although we did not prove it by direct measurement of central aortic pressures or the augmentation index. Mottram and associates [1] reported that arterial compliance is an independent predictor of diastolic dysfunction in patients with hypertensive heart disease and should be considered a potential target for intervention in diastolic heart failure. Similarly, if we can correct the diastolic dysfunction by surgical intervention to enlarge the true lumen, diastolic heart failure can be an operative indication for type B dissection.
It is well established that LV relaxation is often abnormal in the hypertensives with or without LV hypertrophy, suggesting that abnormal relaxation may be an early response to cardiac overload caused by hypertension [15]. In an experimental study using pressure-overloaded rats, Kuwahara and coworkers [16] found that transforming growth factor-ß played a causal role in myocardial fibrosis and diastolic dysfunction through fibroblast activation after pressure overload. The fibrosis began even before the cardiomyocyte grew in diameter [16]. In our study population, diastolic dysfunction was observed without an increase of LV wall thickness. Our result is in accordance with the report by Kuwahara and associates, suggesting that diastolic dysfunction may precede clinical LV hypertrophy.
Study Limitations
Tissue Doppler imaging of the mitral annulus, which has recently been proposed as a method to evaluate diastolic LV function [17] and is reported as effective as flow propagation velocity to estimate LV filling pressure [18], was not used. This is not a prospective study, and the patients background may not be uniform. Because the number of patients is small and we do not have the predissection or postoperative echocardiographic data, we do not know whether LV dysfunction is induced by dissection or is merely an epiphenomenon, nor do we know whether it is reversible. Further study with a larger volume of patients is thus required.
In conclusion, left ventricular diastolic function can be severely reduced in patients with type B chronic aortic dissection that has a double barrel and a narrowed true lumen.
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