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2018年4月26日 星期四

Harrison 讀書筆記:心臟衰竭的病理機轉與診斷

Heart failure:  Pathophysiology  and Diagnosis


A  complex  clinical  syndrome  that  results  from  structural  or  functional  impairment of ventricular filling or ejection of blood, which in turn leads to the cardinal clinical symptoms of dyspnea and fatigue and signs of HF (edema and rales)


Etiology of HF in patients with a preserved EF differs from that of patients with depressed EF, there is considerable overlap.


In industrialized countries,  CAD has  become the predominant cause in men and women and is responsible for 60–75% of cases of HF. 


Hypertension contributes to the development of HF in 75% of patients, 
including most patients with CAD. Both CAD and hypertension interact to augment the risk of HF, as does diabetes mellitus.

20–30% of the cases of HFrEF, the exact etiologic basis is not known, while a large number of cases of  dilated cardiomyopathy  are  secondary  to  specific  genetic  defects

在收縮功能有明顯異常的病例當中,有百分之二十到三十的患者原因不明;而擴張性心肌病變則多跟基因有關(OS: 好倒楣阿)


Recent advances in the evaluation and management of HF, the development of symptomatic HF still carries a poor prognosis. 

Community-based  studies  indicate  that 
30–40% die within 1 year of diagnosis 
60–70% die within 5 years 

mainly from worsening HF or as a sudden event (eg. ventricular arrhythmia). 


HF may be viewed as a progressive disorder that is initiated after an INDEX EVENT


Although  the  precise  reasons  why  patients  with  LV  dysfunction may remain asymptomatic is not certain, one potential explanation is that a number of compensatory mechanisms become activated in the presence  of  cardiac  injury  and/or  LV  dysfunction to sustain and modulate LV function for a period of months to years. 

Heart Failure with a Reduced Ejection Fraction  HFrEF的機轉


Myocardial  relaxation is an  adenosine  triphosphate  (ATP) dependent process that is regulated by uptake of cytoplasmic calcium into the SR by SERCA2A and extrusion of calcium by sarcolemmal pumps (see Fig. 265e-7). Accordingly, reductions in ATP concentration, as occurs in ischemia, may interfere with these processes and lead to slowed myocardial relaxation.

心肌細胞舒張是需要 ATP 的主動運動,所以如果心肌細胞因為某些原因 —— 缺血、缺氧、受損 —— 而使得細胞內的 ATP 濃度下降,心肌細胞的舒張就會不正常(OS:就像重量訓練完伸展是要主動做的)


Alternatively, if LV filling is delayed because LV compliance is reduced (e.g., from hypertrophy or fibrosis), LV filling pressures will similarly remain elevated at end diastole (see Fig. 265e-11). 


An increase in heart rate disproportionately shortens the  time  for  diastolic  filling,  which  may  lead  to  elevated  LV  filling pressures, particularly in noncompliant ventricles. Elevated LV end-diastolic  filling  pressures  result  in  increases  in  pulmonary  capillary pressures, which can contribute to the dyspnea experienced by patients with diastolic dysfunction. 


In addition to impaired myocardial relaxation, increased myocardial stiffness secondary to cardiac hypertrophy and increased myocardial collagen content may contribute to diastolic failure. Importantly, diastolic dysfunction can occur alone or in combination with systolic dysfunction in patients with HF.