摘要
胎儿心律失常及心脏传导异常在日常临床工作中较为常见，在孕妇的检出率为1．3％～24．9％。主要分功能性和器质性两类，功能性多与胎儿心脏发育不完善或母亲饮用含咖啡因类兴奋剂的饮料、食品、烟酒等有关，多为自限型；器质性胎儿心律失常与胎儿心血管畸形、神经系统畸形或胎儿死亡有关。所以，简单易行、准确且重复性高的检测胎儿微弱房室传导异常的诊断方法，在高危胎儿的监测及危险因素评估中具有重要的临床意义，是目前优生优育工作中具有重要意义的研究课题。
本研究的目的是采用组织多普勒成像(TDI)与脉冲多普勒超声心动图(PD)确立正常胎儿的心脏传导时间参考值，探讨孕龄及心率对该值的影响。
资料与方法
一、研究对象
自2006年12月至2007年6月期间在本院接受产科常规检查或胎儿超声心动图检查的孕妇，随机抽取其中201名，12例因发现胎儿先天性心脏病、持续性心律失常、心脏肿瘤或双胎被排除。其余189例孕妇，年龄19～38岁，平均(28±3)岁，孕龄16～41周，平均(30±6)周，符合以下条件作为本研究对象：单胎，产科常规超声检查未见明显异常，胎儿超声心动图未见明显心血管畸形及持续心律不齐，左室流入道及流出道交界处PD频谱E、A及二尖瓣环TDI频谱Ea，Aa、Sa不融合，能够清晰辨认。189例胎儿中17例为阵发性心律失常，作为心律失常组，与自身窦性心律进行比较。
二、仪器与方法
应用GE VIVID7型、PHILIPS IE 33型及Siemens Sequoia 512型彩色多普勒超声诊断仪，探头为M3S、S5-1、8V3C，频率范围为1．7～8．0MHz。PD频谱及TDI频谱扫描速度为50mm／s，必要时调整到100或150mm／s。
1．一般产科检查：确定胎位，测量双顶径、股骨长，以估算胎儿孕龄。以胎儿胎位、脊柱、肝脏、胃泡、降主动脉、卵圆孔膜方向等判别左、右心室。
2．测量：在四腔心切面或五腔心切面将TDI取样容积置于二尖瓣环，取得二尖瓣环的运动速度曲线；将PD取样容积置于左室流入道和流出道交界处，同时取得左室流出道和流入道的血流频谱。测量时尽量使超声束与血流方向平行或夹角<20°。
测量房室传导时间(AV)及心室开始收缩至下一心动周期心房开始收缩的时间间期(VA)。
TDI：二尖瓣环舒张晚期Aa峰起始处认为心房开始收缩，收缩期Sa峰起始处认为是心室开始收缩，测量两者之间的时间间期认为是房室传导时间(TDI-AV)，同时测量收缩期Sa峰开始至下一心动周期的Aa峰起始处的时间间期(TDI-VA)。
PD：左室流入道血流A峰起始处认为心房开始收缩，左室流出道S峰起始处认为是心室开始收缩，测量两者之间的时间间期认为是房室传导时间(PD-AV)，同时测量S峰起始处至下一心动周期A峰起始处的时间间期(PD-VA)。
以上测量均测3个心动周期，取平均值。对于偶发心律失常的胎儿，测量AV、VA时，取心律失常前或后至少3个窦性心动周期以外开始测量；同时测量心律失常时的AV、VA并与自身窦性心率进行比较。
三、统计学分析
采用SPSS 13．0统计学软件包进行分析。计量资料表示为(?)±s，TDI、PD两种方法比较采用配对t检验，胎儿心脏传导时间与孕周、胎心率进行直线相关与回归分析，不同孕周、不同心率胎儿的心脏传导时间比较采用单因素方差分析。P<0．05认为差异有统计学意义。
结果
一、189例胎儿，心脏结构均正常，心律正常172例，偶发心律失常17例，心率55～175bpm。TDI成功测量AV，VA 179例，占94．71％；PD测量AV，VA 183例，占96．83％，测量成功率无明显差异。
二、TDI测量AV为(126．56±15．33)ms，95％CI：(124．10～129．03)ms；VA为(285．22±24．53)ms，95％CI：(281．27～289．16)ms。PD测量AV为(127．42±12．88)ms，95％CI：(125．35～129．49)ms；VA为(287．42±25．19)ms，95％CI：(283．37～291．47)ms。用配对t检验分析TDI、PD两种方法测量AV差异无统计学意义，t=0．306，P=0．760；测量VA差异无统计学意义，t=1．363，P=0．175。
三、AV、VA与孕周呈正相关，与心率呈负相关。PD、TDI两种方法测量AV在不同心率胎儿的比较差异无统计学意义，VA在不同心率胎儿的比较差异有统计学意义；PD、TDI两种方法测量AV、VA在不同孕周胎儿的比较差异无统计学意义。
四、偶发心律失常胎儿17例：4例为心动过缓：其中1例表现为AV、VA均明显延长，1例AV明显延长，2例VA明显延长。13例为房性期前收缩，其中2例为二联律，早搏周期VA均较窦性心率时缩短，其后代偿间歇周期的VA除2例外均明显延长，早搏周期AV、代偿间歇周期AV与窦性心动周期的AV相比无明显改变。
结论
TDI、PD均可简单快速地定量测定胎儿心脏传导时间，胎儿心脏传导时间与胎心率呈负相关，与孕周呈正相关。胎儿房室传导时间参考值的测定对于胎儿心律失常的评估具有重要的临床应用价值。
Irregular fetal heart rhythms are common in clinical practice. Most ofthem are paroxysmal, and heart anatomies are normal. They can restoresinus rhythm without treatment. A few of them may be associated withfetal hydrops, structural heart disease, neurological complications, andfetal demise. So they usually require aggressive treatment to eliminate therisk of cardiac failure. To identify fetuses with arrhythmia, normal valuesfirst have to be obtained.
The aim of present study was to establish reference values of normalfetal heart conduction time intervals by spectral tissue Doppler and pulseDoppler methods, and to assess the influence of both gestational age andfetal heart rate on those intervals.
STUDY POPULATION AND METHODS
From December, 2006 to June, 2007, we randomly enrolled 201consecutive pregnant women, of whom 189 were recruited into study group (age 28±3 years, range 19～38 years, gestation age 30±6 weeks,range 16～41 weeks). Twelve were ruled out because of congenital heartdisease, sustained arrhythmia or bigeminal pregnancy.
A detailed echocardiographic examination was performed with GEVivid-7, Siemens Sequoia 512, or IE 33 ultrasound system with 1.7～8.0MHz sector transducers.
1. General obstetrics examination: Fetal position was assessed andfetal gestational age was estimated by measuring biparetal diameter andfemur length.
2. Left or right ventricle was distinguished by fetal position, spine,liver, aerogastria, descending aorta or the blood direction of foramenovale. In a 5-chamber view with the septum in a vertical position,velocities generated by both the inflow of blood through the mitral valveduring the diastole and by the outflow through the left ventricular outletduring systole were recorded. All TDI measures were obtained fromannulus of mitral valve. Care was taken to direct the transducer beam asclose as possible to the Doppler beam at <20°in selected planes.
2.1 Measure atrio-ventricular conduction time intervals (AV) and thetime intervals from onset of ventricular contraction to the onset of atrialcontraction of next cardiac cycle (VA).
Using TDI approach, the start of the Aa wave which represented themovement of annulus of mitral valve during lated diastolic stage was taken as onset of atrial contraction, and the start of the Sa wave duringsystolic phase was taken as onset of ventricular contraction. TDI-AV wascalculated from the beginning of Aa wave to the beginning of the Sawave, and TDI-VA was from the beginning of the Sa wave to thebeginning of next Aa wave.
Using the pulse Doppler technique, flow-velocity waveforms throughthe mitral valve were recorded with ejection waves toward the aorta byplacing the sample volume in the lower part of the outflow tract of the leftventricle. On these tracings, atrial contraction corresponded to the start ofthe Doppler A wave, and ventricular contraction to the beginning of theventricular ejection wave (S wave) going in the opposite direction. Withthat approach, PD-AV was measured between the start of A wave to thestart of S wave, and PD-VA was between the start of S wave to the startof next A wave.
2.2 To account for slight variations in measurements, each parameterwas measured in 3 consecutive beats and the values averaged to obtaineach interval duration. In fetuses with intermittent arrhythmia, AV andVA measured when arrhythmia were compared with normal sinusrhythm.
3. Statistic analysis
All statistics were carried out using SPSS 13.0 software. A probabilityvalue <0.05 was considered as statistically significant.
RESULTS
1. Two hundred and one fetal echocardiogaphic examinations wereperformed in 201 fetuses, among them 172with normal cardiac structureand normal rhythm, 17 with intermittent arrhythmia, and 12 withcongenital heart disease, sustained arrhythmia or bigeminal pregnancy.
2. TDI-AV is (126.56±15.33) ms, 95%CI: (124.10～129.03) ms.TDI-VAis (285.22±24.53) ms, 95%CI: (281.27～289.16) ms.PD-AVis (127.42±12.88) ms, 95%CI: ( 125.35～129.49) ms. PD-VA is(287.42±25.19)ms, 95%CI: (283.37～291.47)ms. A paired t test directlycompared two approaches used to measure AV and VA, which revealedno systematic difference (t value is 0.306,1.363, respectively, P>0.05).
3. AV and VA were significantly positively correlated with gestationalage, and negatively correlated with fetal heart rate. We divided all fetusesinto different group according to the gestational age or fetal heart rate.The results revealed that VA had significantly difference among differentheart rate groups. AV had no significantly difference among differentheart rate groups. AV, VA had no significantly difference among differentage groups.
4. Heart conduction time intervals were altered in fetus withparoxysmal arrhythmia.
CONCLUTIONS
This study established the normal values of fetal heart conduction times. AV and VA were significantly positively correlated withgestational age, and significantly negatively correlated with fetal heartrate. This investigation suggests important potential clinical utility of fetalheart conductional times in assessing congenital atrio-ventricular block.Further study is warranted.
引文
1 Copel JA, Liang RI, Demasio K, et al. The clinical significance of the irregular fetal heart rhythm. Am J Obstet Gynecol, 2000,182:813 -819.
2 Strasburger JF, Cheulkar B, Wichman HJ. Perinatal arrhythmias: diagnosis and management. Clin Perinatol, 2007,34:627-652, vii-viii.
3 De Wilde H, Benatar A. Cardiac rhabdomyoma with long-term conduction abnormality: progression from pre-excitation to bundle branch block and finally complete heart block. Med Sci Monit, 2007,13:CS21-23.
4 van Leeuwen P, Schiermeier S, Lange S, et al. Gender-related changes in magnetocardiographically determined fetal cardiac time intervals in intrauterine growth retardation. Pediatr Res, 2006,59:820-824.
5 Sant'Anna AM, Fouron JC, Alvarez F. Neonatal cholestasis associated with fetal arrhythmia. J Pediatr, 2005,146:277-280.
6 Hajdu J, Marton T, Toth-Pal E, et al. Familial association of congenital left heart abnormalities and sustained fetal arrhythmia. Pediatr Cardiol, 1999,20:368-370.
7 Vlagsma R, Hallensleben E, Meijboom EJ. Supraventricular tachycardia and premature atrial contractions in fetus. Ned Tijdschr Geneeskd, 2001,145:295-299.
8 D'Alto M, Russo MG, Paladini D, et al. The challenge of fetal dysrhythmias: echocardiographic diagnosis and clinical management. J Cardiovasc Med (Hagerstown), 2008,9:153-160.
9 Prandstraller D, Perolo A, Bronzetti G, et al. Aggressive maternal therapy for fetal arrhythmia. Ultrasound Obstet Gynecol, 2007,30:628.
10 Leake RD, Strimling B, Emmanouilides GC. Intrauterine cardiac failure with hydrops fetalis. Case report in a twin with the hypoplastic left heart syndrome and review of the literature. Clin Pediatr (Phila), 1973,12(11):649-651.
11 Mastronardi R, Presicci V, Ciasca G. Echographic diagnosis of fetal hydrops and ascites. Description of 2 cases of fetal hydrops and ascites caused by congenital immunodeficiency and feto-fetal transfusion syndrome. Etio-pathogenic considerations.Minerva Ginecol,1987,39(5):337-341.
12 Balducci G, Mautone A, Pintucci R, et al. Fetal hydrops caused by cardiac failure in utero: description of 2 cases and pathogenetic considerations. Pediatr Med Chir,1984,6(4):543-547.
13 Stinstra J, Golbach E, van Leeuwen P, et al. Multicentre study of fetal cardiac time intervals using magnetocardiography. BJOG, 2002, 109:1235-1243.
14 Andelfinger G, Fouron JC, Sonesson SE, et al. Reference values for time intervals between atrial and ventricular contractions of the fetal heart measured by two Doppler techniques. Am J Cardiol, 2001, 88: 1433-1436.
15 Nii M, Hamilton RM, Fenwick L, et al. Assessment of fetal atrioventricular time intervals by tissue Doppler and pulse Doppler echocardiography: normal values and correlation with fetal electrocardiography. Heart, 2006,92:1831-1837.
16 Rein AJ, O'Donnell C, Geva T, et al. Use of tissue velocity imaging in the diagnosis of fetal cardiac arrhythmias. Circulation, 2002,106: 1827-1833.
17 Rein AJ, O'Donnell CP, Colan SD, et al. Tissue velocity Doppler assessment of atrial and ventricular electromechanical coupling and atrioventricular time intervals in normal subjects. Am J Cardiol, 2003,92:1347-1350.
18 Bolnick AD, Borgida AF, Egan JF, et al. Influence of gestational age and fetal heart rate on the fetal mechanical PR interval. J Matern Fetal Neonatal Med, 2004,15:303-305.
19 Dancea A, Fouron JC, Miro J, et al. Correlation between electrocardiographic and ultrasonographic time-interval measurements in fetal lamb heart. Pediatr Res, 2000,47:324-328.
20 Pasquini L, Seale AN, Belmar C, et al. PR interval: a comparison of electrical and mechanical methods in the fetus. Early Hum Dev, 2007,83:231-237.
21 van Leeuwen P, Hailer B, Bader W, et al. Magnetocardiography in the diagnosis of fetal arrhythmia. Br J Obstet Gynaecol, 1999, 106:1200-1208.
22 Verklan MT, Padhye NS, Brazdeikis A. Analysis of fetal heart rate variability obtained by magnetocardiography.J Perinat Neonatal Nurs,2006,20(4): 343-348.
23 Sato M, Kimura Y, Chida S, et al. A novel extraction method of fetal electrocardiogram from the composite abdominal signal. IEEE Trans Biomed Eng, 2007,54(1 ):49-58.
24 Nakai K, Fukuhiro H, Kawazoe K, et al. Development of 64-channel magnetocardiography and clinical application. Rinsho Byori,2006, 54(8):844-849.
25 Hosono T. Fetal magnetocardiography. Rinsho Byori, 2006, 54(5):477-485.
26 Respondek M, Wloch A, Kaczmarek P, et al. Diagnostic and perinatal management of fetal extrasystole. Pediatr Cardiol, 1997, 18: 361-366.
27 Szymkiewicz-Dangel J. Fetal arrhythmia—own experience. Med Wieku Rozwoj, 2003,7:241-254.
28 Zhao BW, Zhang SY, Pan M, et al. Clinical application of
echocardiography in detection of foetal arrhythmia:a retrospectivestudy of 451 foetuses.Chin Med J,2004,117:474-477.
29 赵博文，吕江红，潘美，等．组织多普勒成像在胎儿心律失常中的应用研究．中华超声影像学杂志，2006，15：831-835．
30 Van Bergen AH,Cuneo BF,Davis N.Prospective echocardiographicevaluation of atrioventricular conduction in fetuses withmaternal Sjogren's antibodies.Am J Obstet Gynecol,2004,191:1014-1018.
31 Nii M,Shimizu M,Roman KS,et al.Doppler tissue imaging in theassessment of atrioventricular conduction time:validation of a noveltechnique and comparison with electrophysiologic and pulsed waveDoppler-derived equivalents in an animal model.J Am SocEchocardiogr,2006,19:314-321.
32 Fouron JC,Proulx F,Miro J,et al.Doppler and M-modeultrasounography to time fetal atrial and ventricular contractions.Obstet Gynecol,2000,96(5):732-736.
33 Jaeggi E,Fouron JC,Fournier A,et al.Ventriculo-atrial timeinterval measured on M mode echocardiography:a determiningelement in diagnosis,treatment,and prognosis of fetalsupraventricular tachycardia.Heart,1998,79:582-587.
1 Yurci A, Oflaz H, Meric M, et al. Mitral and tricuspid annular velocities determined by Doppler tissue imaging in hypopituitary, growth hormone-deficient patients. Horm Res, 2005,64:107-114.
2 Rowland T, Heffernan K, Jae SY, et al. Cardiovascular responses to static exercise in boys: insights from tissue Doppler imaging. Eur J Appl Physiol, 2006,97:637-642.
3 Notomi Y, Srinath G, Shiota T, et al. Maturational and adaptive modulation of left ventricular torsional biomechanics: Doppler tissue imaging observation from infancy to adulthood. Circulation, 2006,113:2534-2541.
4 Brili S, Alexopoulos N, Latsios G, et al. Tissue Doppler imaging and brain natriuretic peptide levels in adults with repaired tetralogy of Fallot. J Am Soc Echocardiogr, 2005,18:1149-1154.
5 Tuller D, Steiner M, Wahl A, et al. Systolic right ventricular function assessment by pulsed wave tissue Doppler imaging of the tricuspid annulus. Swiss Med Wkly, 2005,135:461-468.
6 Tutschek B, Zimmermann T, Buck T, et al. Fetal tissue Doppler echo cardiography: detection rates of cardiac structures and quantitative assessment of the fetal heart. Ultrasound Obstet Gynecol, 2003, 21 (1): 26-32.
7 Zilberman MV, Du W, Das S, Sarnaik SA. Evaluation of left ventricular diastolic function in pediatric sickle cell disease patients. Am J Hematol, 2007 Jun;82(6):433-438
8 Acharya G, Rasanen J, Makikallio K, et al. Metabolic acidosis decreases fetal myocardial isovolumic velocities in a chronic sheep model of increased placental vascular resistance. Am J Physiol Heart Circ Physiol, 2008,294:H498-504.
9 Gardiner HM, Pasquini L, Wolfenden J, et al. Myocardial tissue Doppler and long axis function in the fetal heart. Int J Cardiol, 2006,113:39-47.
10 D'Alto M, Russo MG, Paladini D, et al. The challenge of fetal dysrhythmias: echocardiographic diagnosis and clinical management. J Cardiovasc Med (Hagerstown), 2008,9:153-160.
11 Huhta JC, Kales E, Casbohm A.Fetal tissue Doppler～a new technique for perinatal cardiology. Curr Opin Pediatr, 2003 Oct;15(5):472-474.
12 Jamjureeruk V.Some aspects of fetal echocardiogram: 12 years of experience.J Med Assoc Thai,2003,86 Suppl 1:S36-45
13 Steinhard J, Heinig J, Schmitz R, et al. Tissue Doppler imaging of the fetal heart--a new parametric ultrasound technique in prenatal medicine. Ultraschall Med, 2007,28:578-583.
14 Lu Y, Deng Y, Liu Y, et al. Evaluation of normal fetal left cardiac function by tissue Doppler imaging. J Huazhong Univ Sci Technolog Med Sci, 2006,26:251-253
15 Sklansky M. Advances in fetal cardiac imaging. Pediatr Cardiol,2004,25(3):307-321. Review.
16 Harada K, Tsuda A, Orino T, et al. Tissue Doppler imaging in the normal fetus. Int J Cardiol, 1999,71 (3): 227-234.
17 Harada K, Ogawa M, Tanaka T. Right ventricular pre-ejection myocardial velocity and myocardial acceleration in normal fetuses assessed by Doppler tissue imaging. J Am Soc Echocardiogr, 2005,18 (4): 370-374.
18 Paladini D, Lamberti A, Teodoro A, et al. Tissue Doppler imaging of the fetal heart. Ultrasound Obstet Gynecol, 2000,16(6):530-535.
19 Jamjureeruk V. Evaluation of ventricular myocardial velocities and heart motion of the fetal heart by tissue Doppler image. J Med Assoc Thai, 2001,84(8): 1158-1163.
20 Deng J, Rodeck CH. Current applications of fetal cardiac imaging technology. Curr Opin Obstet Gynecol, 2006,18:177-184.
21 Aoki M, Harada K, Ogawa M, et al. Quantitative assessment of right ventricular function using Doppler tissue imaging in fetuses with and without heart failure. J Am Soc Echocardiogr, 2004,17(1):28-35.
22 Chan LYS, Fok WY, Wong JTH, et al. Reference charts of gestation-specific tissue Doppler imaging indices of systolic and diastolic functions in the normal fetal heart. Am Heart J ,2005,150 (4): 750-755.
23 Pacileo G, Paladini D, Russo MG, et al. Echocardiographic assessment of ventricular filling pressure during the second and third trimesters of gestation. Ultrasound Obstet Gynecol, 2000,16(2):128-132.
24 Nagueh SF, Middleton KJ, Kopelen HA, et al. Doppler tissue imaging: a noninvasive technique for evaluation of left ventricular relaxation and estimation of filling pressue. J Am Coll Cardiol, 1997,30:1527-1533.
25 Nii M, Roman KS, Kingdom J, et al. Assessment of the evolution of normal fetal diastolic function during mid and late gestation by spectral Doppler tissue echocardiography. J Am Soc Echocardiogr, 2006,19:1431-1437.
26 Uematsu M, Miyatake K, Tanaka N, et al. Myocardial velocity gradient as a new indicator of regional left ventricular contraction: detection by a two-dimensional tissue Doppler imaging technique. J Am Coll Cardiol, 1995,26:217-223.
27 Rychik J, Tian ZY. Quantitative assessment of myocardial tissue velocities in normal children with Doppler tissue imaging. Am J Cardiol, 1996,77:1254-1257.
28 Acharya G, Pavlovic M, Ewing L, et al. Comparison between
pulsed-wave Doppler- and tissue Doppler-derived Tei indices infetuses with and without congenital heart disease.Ultrasound ObstetGynecol,2008.[Epub ahead of print]
29 Szymkiewicz-Dangel J,Hamela-Olkowska A,Wlasienko P,et al.The possibility of evaluation of the myocardial performance index infetuses at 11,0 to 13,6 week of gestation.Ginekol Pol,2007,78:218-222.
30 Lu G,Wang Z,He S,et al.Changes in the Tei index during acutefetal hypoxemia in the near-term ovine fetus after intermittentumbilical cord occlusion.Ultrasound Obstet Gynecol,2007.[Epubahead of print]
31 Guorong L,Shaozheng H,Zhenghua W,et al.Tei index for prenataldiagnosis of acute fetal hypoxia due to intermittent umbilical cordocclusion in an animal model.Prenat Diagn,2007,27:817-823.
32 章明，周启昌，彭清海等．组织多普勒成像评价正常胎儿左、右室Tei指数的研究．中国超声医学杂志，2005，21(2)：136-138．
33 P.Twining.Myocardial motion imaging:a new application of powercolor flow and frequency-based color flow Doppler in fetalechocardiography.Ultrasound Obstet Gynecol ,1999,13:255-259.
34 Ayres NA.Advances in fetal echocardiography.Tex Heart Inst J,1997,24 (4):250-259.
35 Zhao BW,Zhang SY,Pan M,et al.Clinical application of echocardiography in detection of foetal arrhythmia: a retrospective study of 451 foetuses. Chin Med J (Engl), 2004,117:474-477.
36 Szymkiewicz-Dangel J. Fetal arrhythmia--own experience. Med Wieku Rozwoj, 2003,7:241-254.
37 Hajdu J, Marton T, Toth-Pal E, et al. Familial association of congenital left heart abnormalities and sustained fetal arrhythmia. Pediatr Cardiol, 1999,20:368-370.
38 Todros T, Presbitero P, Gaglioti P, et al. Conservative management of fetal bigeminy arrhythmia leading to persistent bradycardia. Eur J Obstet Gynecol Reprod Biol, 1990,34:211-215.
39 Copel JA, Liang RI, Demasio K, et al. The clinical significance of the irregular fetal heart rhythm. Am J Obstet Gynecol,2000,182:813-819.
40 Robinson HP, Shaw-Dunn J. Fetal heart rates as determined by sonar in early pregnancy. J Obstet Gynaecol Br Commonw, 1973,80:805-809.
41 Jaeggi E, Fouron JC, Fournier A, et al. Ventriculo-atrial time interval measured on M mode echocardiography: a determining element in diagnosis, treatment, and prognosis of fetal supraventricular tachycardia. Heart, 1998,79:582-587.
42 Nii M, Shimizu M, Roman KS, et al. Doppler tissue imaging in the assessment of atrioventricular conduction time: validation of a novel technique and comparison with electrophysiologic and pulsed wave Doppler-derived equivalents in an animal model. J Am Soc Echocardiogr, 2006,19:314-321.
43 Cotton JL. Identification of fetal atrial flutter by Doppler tissue imaging. Circulation, 2001,104(10):1206-1207.
44 Rein AJ, Levine JC, Mr A. Use of high-frame rate imaging and Doppler tissue echocardiography in the diagnosis of fetal ventricular tachycardia. J Am Soc Echocardiogr, 2001,14(2):149-151.
45 Rein AJ, O'Donnell C, Geva T, et al .Use of tissue velocity imaging in the diagnosis of fetal cardiac arrhythmias. Circulation, 2002,106(14):1827-1833.