摘要:背景 右心室出口在心室心律不整所扮演的角色在最近幾年逐漸受到重視。對於不明原因心室心博過速,Brugada氏症候群,心律不整型右心室病變,及先天性心臟病術後的病人,心室心律不整常源起於右心室出口。在這些右心室出口疾病中,法洛氏四重症可以算是一種典型的疾病模式,也是成人族群最常見的右心衰竭原因之一。這些法洛氏四重症病人即使完全矯正後,長期追蹤仍有一定比例的人有心室心律不整及心因性猝死的風險。這些晚期心律不整及死亡的原因有相當多研究,包括機械因子與電氣生理的交互作用,然而確實的電生理機轉仍未知,而心律不整藥物對於這些法洛氏四重症及右心出口疾病病人的預防效果也仍不明。心室心律不整是心因性猝死最主要原因,其電生理機轉在左心室疾病已有許多研究。再極化異質性被認為是一個重要原因,而心電圖上可顯示T波交替(T wave alternans),這些微小T波交替對於擴張性心肌病變及瀕臨猝死病患之後心室心律不整及猝死有好的預測度。不只多型性心室心博過速及心室顫動,再極化異質在同時有結構障礙如疤痕時,也容易誘發出單型性心室心博過速。之前研究在左心衰竭模式發現T波交替的機轉與心肌細胞的動作電位間距交替(Action potential duration alternans)有關。通常動作電位間距交替在越短的電刺激週期時間(pacing cycle length)會越明顯,當數值超過10毫秒及變的不均質化(inhomogeneous)時就容易有心室心律不整。這種不一致交替(discordant alternans)可以導致足夠陡的空間再極化電位梯度,就會造成單一方向傳導障礙極再迴繞,而導致心室顫動。過去許多研就嘗試解釋動電位間距交替的機轉,包括(1)鈣離子循環的異質化及交替,(2)傳導速度回復曲線斜率較陡,(3)細胞內電位去偶合。但是對於正常及有疾病的右心室出口相關的細胞電生理研究卻相當稀少。我們藉由右心出口切開及跨瓣膜補片手術,肺動脈瓣膜破壞,及右側傳導支電燒,建構了一個新的法洛氏四重症狗的動物模式。因為同時合併右心出口心臟衰竭及心室心律不整,所以是研究右心出口心律不整的最佳模式。目標 臨床部分我們回溯性研究我們醫院所有法洛氏四重症術後病人並試圖找出抗心律不整藥物與危及生命事件的相關。基礎部分 藉由心肌細胞光學構圖法(optical mapping),我們首先研究正常右心出口心外膜及心內膜的電氣生理特徵,其次我們藉由同樣實驗,找出法洛氏四重症動物模式心室心律不整機轉,最後,我們研究抗心律不整藥物的效果。方法 臨床部分我們回溯性找出所有在1972至2014年在台大醫院追蹤,且年齡大於15歲的法洛氏四重症病患。紀錄第一次診斷心室心律不整的時間及使用的抗心律不整藥物。我們以死亡,心臟移植,及心內去顫器植入做為研究終點,觀察抗心律不整藥物與研究終點的關係。基礎部分 (1) 正常右心室出口光學構圖法九隻狗將用來研究正常右心室出口,我們取出右心室出口並帶有右冠狀動脈,藉由Langendorff心臟灌流法,我們對於心內膜及心外膜進行雙光學構圖法,同時研究動作電位及鈣離子瞬變電流,並計算動作電位間距交替,鈣離子瞬變電流交替及動作電位間距回復曲線。之後並輸注貝他阻斷劑及amiodarone,重複上述試驗觀察藥物對於上述參數的影響。(2) 疾病右心室出口光學構圖法我們藉由九隻法洛氏四重症動物模式來研究。術後一年進行光學構圖法分析,紀錄心內膜的研究動作電位及鈣離子瞬變電流,重複上述計算。之後並給予輸注藥物來觀察抗心律不整藥物的效果。(3) 我們也將偵測連接蛋白connexin 40和43 及Ito(短暫向外鉀離子電流)的mRNA表現量,並觀察其與動作電位間距交替及心室心律不整之間的關係。初步結果1. 在我們的法洛氏四重症動物模式中,藉由比較第一隻法洛氏四重症術後動物與對照組,我們發現動作電位間距交替及鈣離子瞬變電流交替都在較長的電刺激週期時間即產生,這也暗示動作電位間距交替及鈣離子瞬變電流交替在法洛氏四重症心室心律不整扮演重要角色。2. 在第一隻法洛氏四重症動物模式中,我們見到空間不一致交替較對照組明顯。預期結果1. 藉由臨床研究,我們可以知道心室心律不整發生率及對於法洛氏四重症心室心律不整有效的預防藥物。2. 藉由基礎研究,首先我們可以知道右心室出口特別的細胞電生理變化,可能與左心室不同;其次,藉由法洛氏四重症動物模式,我們可以了解疾病右心室出口的心室心律不整致病機轉;最後,我們也可知道抗心律不整藥物效果及其電生理機轉。
Abstract: BackgroundThe role of right ventricular outflow tract (RVOT) on the genesis of ventricular arrhythmia has gained much attention in recent years. For idiopathic ventricular tachycardia, Brugada syndrome, arrhythmogenic right ventricular dysplasia, and repaired congenital heart disease, ventricular arrhythmia often origin from RVOT. Among these RVOT lesions, repaired tetralogy of Fallot (TOF) is one of the most common causes of right heart failure even in adult population. Even after surgical repair, patients of TOF still pose certain risk of ventricular arrhythmia related sudden cardiac death during long term follow-up. The mechanism of the late mortality and late ventricular arrhythmia in these TOF patients has been studied, and mechano-electrical interaction from hemodynamic factors (RVOT dilatation and right ventricular failure) and electrophysiological factors (prolong QT interval) was proposed as possible important causes. However, the exact electrophysiological mechanism is still unclear, and the effect of antiarrhythmia agents on the prevention of ventricular arrhythmia in repaired TOF and other RVOT disease is still not known.Ventricular arrhythmia is the most important cause of sudden cardiac death, and its mechanisms in left ventricle has been studied for many years. Repolarization heterogeneity, manifested as T wave alternans in surface EKG, is regarded as one of the most important mechanisms. The new diagnostic tools could detect microvolt T wave alternans (MTWA) and is found to have good predictive value for the ventricular arrhythmia and sudden death in dilated cardiomyopathy and aborted sudden cardiac death patients. Not only for polymorphic ventricular tachycardia (VT) or ventricular fibrillation, repolarization heterogeneity could induce monomorphic VT in the presence of structural barrier. Therefore, repolarization heterogeneity is regarded as an important and requisite common pathway of ventricular arrhythmia.In the left heart failure model, the cellular mechanism of T wave alternans was found to relate to action potential duration alternans (APD-ALT). The APD-ALT increased with shorter pacing cycle length, and often exceeded 10ms and became inhomogeneous before ventricular arrhythmia occurred. This discordant alternans can lead to sufficiently steep spatial repolarization gradients so as to produce unidirectional conduction block and functional reentry, resulting in ventricular fibrillation. Several mechanisms have been proposed to explain the APD-ALT, and include (1) spatial heterogeneities and alternans of calcium cycling, (2) steeper conduction velocity restitution slope, and (3) intercellular uncoupling due to down regulation of connexin proteins. Previous studies had proved the importance of above mechanisms on the ventricular arrhythmia in left ventricle. However, the study about cellular electrophysiology in normal and diseased RVOT was very limited.We have created a novel canine repaired TOF model by using right ventricular outflow tract (RVOT) incision with transannular patch creation, pulmonary valve destruction, and right bundle branch ablation. This model is a perfect model to study the mechanism of ventricular arrhythmia in diseased RVOT.Aim Clinical Part We will retrospectively reviewed the all repaired TOF patients in our hospital and try to find out the association of antiarrhythmia medication effect and life-threatening events in these TOF patients.Basic part Using optical mapping methods, first, we will study the electrophysiological characteristics of the epicardium and endocardium of normal RVOT. Second, we will find the underlying mechanism of ventricular arrhythmia using rTOF model. Third, the effect of antiarrhythmia agents will be studied.MethodsClinical Part We retrospectively reviewed the records of all our TOF patients older than 15 years of age in National Taiwan University Hospital between 1972 and 2014. The date of first-time diagnosis as ventricular arrhythmia and antiarrhythmia medication used will be recorded. Then we will find the primary end-point including death, heart transplantation, and implantation of implantable cardioverter defibrillator in these patients. We will correlate the antiarrhythmia medication with the primary end-point to see its effect.Basic part (1) Normal RVOT optical mapping Nine canines will be used for normal RVOT study. We will then harvest the RVOT wedge with right coronary artery pedicle. Using Langendorff perfusion technique, we then perform dual optical mapping on both endocardium and epicardium for APD and Ca transient recording. The conduction velocity, APD alternans, and calcium alternans will then calculated. Then we will perfuse RVOT wedge with the beta-blocker and amiodarone and pace again to see their effects on above parameters.表 C011 共 2 頁 第 1 頁(2) Diseased RVOT optical mapping For the diseased RVOT, we will use repaired TOF model for analysis. One year after intervention, the optical mapping will be performed to analyze these electrophysiological parameters and antiarrhythmia effect.(3) Effect of connexin proteins and transient outward current effect on the APD-ALT and Ca-ALT will be defined by checking the connexin 40, 43 mRNA expression and Ito mRNA expression.Preliminary Result1. We found the pulmonary regurgitation, right ventricular outflow tract dilatation, QRS duration prolongation, and ventricular arrhythmia episodes were all significantly higher with follow-up duration in the repaired TOF animals. From the comparisons of one repaired TOF animal and control animal, we found the APD-ALT and Ca-ALT all began at longer pacing cycle length in the repaired TOF model. This may indicate the APD-ALT may play an important role of ventricular arrhythmia in the repaired TOF.2. In the repaired TOF model, we can see the spatially discordant alternans is more prominent than control group.Predicted Outcome1. From clinical study, we can know the incidence of ventricular arrhythmia in and know the most effective preventive medication in repaired TOF patients.2. From basic part, first, we can know the special cellular electrophysiology of the RVOT which may be different from left ventricle. Second, from the repaired TOF model, we can further define the underlying mechanism of ventricular arrhythmia in repaired TOF and diseased RVOT. Third, the antiarrhythmia effect and its cellular electrophysiological mechanism will be delineated also.