Pathophysiology

• pathophysiology of DHF is not completely understood
  • generally there is impaired left ventricular relaxation, particularly during exercise, probably due to changes in cytoskeletal proteins; and increased left ventricular diastolic stiffness due to increased myocardial mass and fibrosis
    • subtle abnormalities of systolic function are also frequently present
  • impaired left ventricular relaxation is greatly exacerbated during exercise
  • increased large artery stiffness (manifest as systolic hypertension) also appears to play a key role
    • net effect is impaired LV diastolic filling resulting in higher diastolic pressures with consequent pulmonary congestion and a reduced ability to increase cardiac output
    • impairment of left ventricular filling can also result in episodes of acute pulmonary oedema ("flash pulmonary oedema") often precipitated by the development of atrial fibrillation and/or fluid retention
      
      
• Cardiac Physiological Factors
  • Diastolic Dysfunction
    • inability to fill the ventricle to an adequate preload volume, diastolic dysfunction is at the core of heart failure with preserved ejection fraction
      • such as in obesity changes in diastology are a primary dysfunction whereas in others such as prolonged hypertension they reflect other factors that change the loading conditions upon the heart
      • effect of diastolic dysfunction becomes more pronounced upon exercise:
        • the filling time remains prolonged, meaning the ventricle cannot completely fill in between beats, further reducing efficiency
          
          
  • Chronotropic Incompetence
    • inability to increase heart rate on exertion is frequently reported in HFpEF
      • seems to correlate with feelings of breathlessness
        
        
  • Systolic Dysfunction
    • though overall ejection fraction is preserved, deficiencies in global longitudinal strain are identifiable, even in those with ejection fraction greater than 55%, indicating subtle systolic impairment
      • limitations are frequently seen during stress in the HFpEF group
        
        
  • Atrial Dysfunction
    • where the diastolic function of the left ventricle is impaired, the left atrium gains greater importance and HFpEF patients may be more reliant upon the LA's booster function
      • loss of atrial contractile function occurs progressively (again, especially under stress) and it has also been observed that HFpEF patients tolerate atrial fibrillation very poorly
      • when the left atria from patients with HFpEF and HFrEF are compared, there is a greater degree of stiffening in HFpEF, perhaps contributing to the rise in pulmonary pressures
        
        
  • Right Ventricular Dysfunction / Pulmonary Vascular Disease
    • even discounting the effects of elevated pulmonary artery pressures, there is both systolic and diastolic impairment of the right ventricle, much in the same way as the left
    • pulmonary vascular resistance itself is also commonly elevated (raising the PA pressures above the results of left atrial hypertension)

Reference:

• BHF Factfile 4/2010. Diastolic Heart Failure.
• Watson W. Heart Failure with Preserved Ejection Fraction: Pathologies, Aetiology and Directions for Treatment. British Cardiovascular Society Editorials (Accessed 9/11/19)