從心室節律刺激模式探討心臟不同步收縮與心衰竭的發生

Abstract

左心室收縮次序的異常因為會造成有協調性的左心室收縮無法維持而被認為是有害的，特別是在極度收縮次序異常的情況，如左隻完全傳導阻斷和右心室電擊刺激的情況。 這些傳導的障礙不但造成了不同步的心臟收縮也造成了不同步的心臟舒張，進而傷害的左心室的整體表現。 許多大規模的臨床研究也證明即使是在維持心房心室同步收縮的情況下，右心室電擊刺激會增加心房顫動的發生率和心衰竭住院的發生率。 雖然只有一小部分的病人在置放了右心室尖端電極導線的心臟節律器刺激後會產生心衰竭，有許多的觀察性研究已經發現右心室電擊刺激會對左心室的功能和型態產生有害的影響。 人工的右心室電擊刺激因為最早的啟動電極波是由右心室尖端經由局部心肌細胞像左心傳遞而不經由His-Purkinje system，而造成左心室的去同步化，這種不正常電波傳導的結果會造成左心室中隔會先收縮並且拉扯遠端尚未收縮的左心室側壁。 接著被拉扯的左心室側壁需要耗費更多的能量去收縮並拉扯已經收縮的其他部位。 這種不正常的拉扯是造成不良的組織再型化過程的關鍵因子。 在右心室尖端施予電擊刺激是用來治療心跳過慢的主要方式，但是在許多的大型臨床研究中已經證明會增加心衰竭的住院率。 在MOST這個大型臨床研究的子研究中也已經證明心衰竭發生的危險性和累積心室擊發的比率成正比，而和心臟節律器的模式是DDD或VVI沒有關係。 最近在新英格蘭醫學期刊發表的臨床研究也顯示，即使在原本收縮功能正常的心臟上，施予傳統右心室尖端電擊刺激會導致左心室射出率的下降和不良的左心室再型化，而這些不良的效應再施予心室節律器的那組病人並沒有出現。 這些臨床的發現暗示經由右心室電擊刺激引起的心室去同步化會引起較高比率的心衰竭發生率。 但是以正常結構心臟模是為研究基礎，右心室電擊刺激引起的的不良效應在分子學階段的證據仍然不足。 為了研究右心室電擊刺激所造成左心室不良再型化的效應，我們收集了116位因為心跳過慢而必須植入永久性心臟節律器的病人，包括80個竇房節功能失常和36個完全房室傳導阻斷的病人，其中76個是接受DDDR型心臟節律器 (其中40個是竇房結功能異常) ，40個是接受AAIR型心臟節律器 (全部都是竇房節功能異常) 。 這些病人都接受血漿中N端原生B型利鈉肽的測量和以心臟超音波測量左右心室間和左心室內機械性心臟不同步收縮的程度，同時在將其他臨床上各種相關因素加入，以回溯性方式做關聯性的研究。 DDDR組和AAIR組兩組病人的心血管功能在心臟節律器裝置之前是相似而沒有差別的，但是在經過平均3.5年的長期節律刺激後，DDDR病人血中N端原生B型利鈉肽的值為503±111 pg/ml，明顯高於AAIR 病人組的194±42 pg/ml，p值為0.002，我們以所有病人血漿中N端原生B型利鈉肽的最高四分位386 pg/ml為截斷值，當成潛在性心衰竭族群，以多變數邏輯性回歸分析探討發現，左右心室間不同步收縮的指標 (左右心室間收縮時間差) 是唯一的決定因素 (每10微秒，p值為0.01) 。 我們將其中8位是因為竇房節功能異常而裝置DDDR型節律器而且合併血中N端原生B型利鈉肽升高的病人，調整其心臟節律器的設定，拉長心房心室收縮延遲後，有效的降低了心室累計擊發的比率，這些病人血中N端原生B型利鈉肽的濃度也同時顯著的下降。 從以上的臨床實驗我們發現主要經由右心室電擊刺激造成的心室間不同步收縮，在具有正常基礎左心室收縮功能的一般病人上，長期DDDR模式右心室尖端電擊刺激後會導致血中N端原生B型利鈉肽濃度不正常的上升。 為了研究在左心室去同步化後，心室內心肌肥厚和心肌收縮相關蛋白表現的改變和細胞外間質再型化的變化，我們採用了一個以狗裝置右心房感應右心室擊發的動物研究模式。 總共六隻狗進行了雙腔室心臟節律器 (DDD) 植入和房室結的電燒灼術，實驗組接受了十二個星期的右心房感應右心室擊發的電擊刺激，我們以心臟超音波中的班塊追蹤技術來測量左心室不同步收縮的情形。 另外有四隻狗是對照組，接受假手術植入心臟節律器，但是心臟節律器維持在關閉的狀態。 經過了十二個星期的右心房感應合併強制右心室擊發的電擊刺激後，左心室被拿下來區分為左心室中隔和左心室側壁做進一步的分析。 心肌收縮相關蛋白，包括sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) 和phospholamban，心肌肥厚相關蛋白，包括 phospho-p38、phospho-ERK和phospho-JNK的表現，心肌細胞外間質再型化相關蛋白tissue inhibitors of metalloproteinase-1 (TIMP-1)、TIMP-3表現和matrix metalloproteinase-2 (MMP-2) 、MMP-9凝膠脢譜活性，心臟不同種類膠原蛋白的RNA表現，與及組織學的變化，在左心室內不同的相對位置做進一步的檢查和分析，以確認是否可能有因為右心室擊發引起的細胞外間質再型化。 在接受右心電擊刺激的實驗組和對照組相比，有明顯的電氣性心臟不同步收縮和機械性心臟不同步收縮。 在實驗組中最晚被啟動收縮的左心室側壁和對照組相比，sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) 的表現有23%的下降，phospholamban的表現則有32%的下降，但是，phospho-p38的表現有2.2倍的升高、phospho-ERK的表現有1.9倍的升高、phospho-JNK的表現則有3.6倍的升高，但是在最早收縮的左心室中隔，實驗組和對照組兩組之間收縮和肥厚相關蛋白的表現沒有顯著的差異。 在細胞外間質的分析方面，和對照組相比，實驗組的左心室側壁表現出明顯間質性纖維化的增加和心肌纖維的裂解，實驗組的纖維化比例為8.3 ± 1.5% 而對照組為3.9 ± 0.9%，P值小於0.01。 在實驗組的左心室側壁第二型膠原蛋白的訊息RNA表現和對照組相比有2.10 ± 0.70倍的顯著增加，P值小於0.01。 但是第一型膠原蛋白訊息RNA在實驗組的左心室側壁的表現雖然有增加，和對照組相比仍然未達統計上的意義。 凝膠脢譜活性測量發現在實驗組的左心室側壁和左心室中隔和對照組相比MMP-9的活性都增加了 (在左心室側壁，實驗組有1.88 ± 0.29倍的增加，P值為小於0.01；在左心室中隔，實驗組有1.45 ± 0.19倍的增加，P值小於0.01) ， 但是MMP-2的活性只有在實驗組的左心室側壁增加 (1.58 ± 0.04 倍，P值小於0.01) ，在實驗組的左心室中隔和對照組相比並沒有顯著的差別。 免疫螢光染色的結果也確認在實驗組左心室側壁MMP-2和MMP-9的活性較對照組有顯著的增加。 另外TIMP-1和TIMP-3的蛋白表現在實驗組的左心室側壁較對照組也是有顯著的增加 (TIMP-1在實驗組左心室側壁有1.23 ± 0.16倍的增加，P值小於0.05；TIMP-3在實驗組左心室側壁有1.98 ± 0.27倍的增加，P值為0.01) 。 從以上的動物實驗結果可以發現，右心室尖端電擊刺激造成心肌收縮時間次序的不一致會引起左心室內不同部位蛋白表現的不一致性。 右心室尖端電擊刺激引起的左心室不同步收縮同時也引起左心室內不一致的細胞外間質再型化。 這些發現有助於我們了解左心室去同步化後引起的病理生理機轉。

Activation sequence abnormality in the left ventricle (LV) is considered harmful to the maintenance of orchestrated cardiac contraction, especially in patients with left bundle branch block and right ventricular (RV) pacing. The conduction disturbance creates both dyssynchronous contraction and relaxation of the LV that is harmful to LV global performance. Large clinical studies have demonstrated ventricular pacing is associated with increased atrial fibrillation and hospitalization for heart failure even with maintenance of atria-ventricular (AV) synchrony. Though only a proportion of patients develop heart failure after receiving RV apical pacing, several observational studies have reported detrimental effects of RV pacing on LV function and morphology. Artificial right ventricle (RV) apical pacing creates LV desynchronization by initiating impulse from local myocardium and bypassing His-Purkinje system. The consequence of abnormal impulses conduction is LV septum contracts first and stretches the not-yet-activated remote LV lateral wall. The stretched LV lateral wall requires more energy to contract and stretch the other regions that are already activated. This abnormal stretching is a key mediator of the adverse tissue remodeling process. RV apical pacing as a treatment modality for bradyarrhythmia has demonstrated to increase the incidence of heart failure hospitalization in many long-term clinical studies. The MOST trial demonstrated that the risks of heart failure development were proportional to cumulative ventricular pacing burden regardless of pacing mode. The recent study also reported traditional RV apical pacing resulted in a reduction in the LV ejection fraction and adverse LV remodeling in patient with pre-existing normal systolic function and these effects were prevented by biventricular pacing. These clinical findings implicate that ventricular desynchronization by RV apical pacing is associated with a higher incidence of heart failure development. But molecular evidence of RV pacing associated adverse effects based on a structurally normal heart model is still lacking.

To investigate the contribution of right ventricular (RV) apical pacing to the left ventricular (LV) negative remodeling, we measured the inter- and intra-ventricular mechanical dyssynchrony by echocardiography as well as plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) level in 116 consecutive patients of symptomatic bradyarrhythmias including sinus node dysfunction (SND) in 80 and atrioventricular block (AVB) in 36. DDDR pacemakers were implanted in 76 patients (SND, 40), and AAIR pacemakers in 40 (all SND). Clinical manifestations were retrospectively correlated. After 3.5 years of chronic pacing, DDDR pacemaker patients demonstrated higher plasma NT-proBNP concentration (503±111 pg/ml) than AAIR patients (194±42 pg/ml, p=0.002) despite similar cardiovascular function in baseline. Multivariate regression analysis revealed that the only predictor of the highest quartile of plasma NT-proBNP, i.e.≧ 386 pg/ml, was the IVTD (per 10 msec, p= 0.01). Reprogramming to minimize ventricular pacing % in 8 patients of SND caused parallel reduction of plasma NT-proBNP. Interventricular mechanical dyssynchrony, imposed mostly by RV apical pacing, could lead to abnormal heightening of plasma NT-proBNP concentration after chronic DDDR pacing in common pacemaker patients with normal baseline LV function. To investigate contraction and hypertrophy-related protein expression changes and extracellular matrix (ECM) remodeling of the LV by desynchronization. We performed the animal study with atria-sensed RV apical pacing in dogs. Six dogs underwent dual chamber pacemaker (DDD) implantation and AV nodal catheter ablation. The pacing group received atria-sensed RV apical pacing for 12 weeks. LV dyssynchrony was assessed with speckle tracking technique. Another 4 dogs was sham-operated for pacemaker implantation only and their pacemakers were kept as off status. After 12 weeks of atria-sensed obligatory RV pacing, LVs were separated into septum and lateral wall for analysis. Contraction-related protein, including sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) and phospholamban, and hypertrophy-related protein, including phospho-p38, phospho-ERK and phospho-JNK expression, zymographic activity, including matrix metalloproteinase-2 (MMP-2), MMP-9, tissue inhibitors of metalloproteinase-1 (TIMP-1), TIMP-3, collagen transcript expression, and histology were examined in opposite portions of the LV to identify possible ECM remodeling changes by RV apical pacing. Both electrical and mechanical dyssynchrony were evident in RV paced dogs compared to sham-operated dogs. The late-activated LV lateral wall of paced dogs displayed a 23% reduction in the amount of sarcoplasmic reticulum Ca2+ ATPase, a 32% reduction in phospholamban levels, but a 3.6-fold increase in phospho-JNK expression, a 2.2-fold increase in phospho-p38, and 1.9-fold increase in phospho-ERK expression. There were no significant differences in the early-activated LV septum between paced and sham dogs. For ECM analysis, compared with sham-operated dogs, increased interstitial fibrosis and fragmentation of myofibrils was found in the LV lateral wall in the pacing group (8.3 ± 1.5% in pacing group vs 3.9 ± 0.9% in sham group, P < 0.01);. Collagen type II mRNA showed a significant 2.10 ± 0.70 fold increase in the LV lateral wall in the pacing group (P < 0.01). While collagen type I mRNA was increased, the difference was not significant. Zymography demonstrated MMP-9 activity was enhanced in both the LV lateral wall and septum in the pacing group (1.88 ± 0.29 fold, P < 0.01 in the LV lateral wall and 1.45 ± 0.19 fold, P < 0.01 in the LV septum), but MMP-2 activity was enhanced in the LV lateral wall (1.58 ± 0.04 fold, P < 0.01). Immunfluorescence stain confirmed the activation of MMP-2 and MMP-9 in the LV lateral wall in the pacing group. Protein expression of TIMP-1 and TIMP-3 showed regional differences in the pacing group and both proteins were increased in the LV lateral wall (1.23 ± 0.16, P < 0.05 for TIMP-1 and 1.98 ± 0.27, P < 0.01 for TIMP-3). Temporal dispersion of mechanical activation by RV apical pacing induced spatial dispersion of protein expression in the LV. LV dyssynchrony by RV apical pacing also elicits heterogeneous ECM remodeling in the LV. These findings assist in the elucidation of the pathophysiology of LV desynchronization.