Posts Tagged ‘heart rate and diastolic function’

Heart is mainly perceived  as  a pumping organ but it need to be realised it  also has a   reservoir function  (Temporarily though , for  about .5 seconds every beat ) . Contrary  to the popular belief heart is not  continuously and tirelessly working  .For every contractile  beat it takes  a brief period of rest .This is called diastole. But , even here it is not a complete rest , as  it has to receive the blood from the atria and get filled and be ready for the next beat.

Many think diastole is an active energy-consuming process . . . but it can be debated still ,  as passive elastic properties may contribute substantially to cardiac relaxation blunting the energy requirement

God is so scientific (Greatest scientist !)  he  made it sure   the resting phase(Diastole)   is slightly more  than the contractile phase (Systole ).

This makes the organ relax a bit more than it stresses  in its entire life time . At  any  given heart rate diastole will be slightly  more than systole  , peculiarly  for the same reason  during tachycardia  diastole suffers more than systole.

What happens in diastolic dysfunction ?

Pathologically the ventricles become stiff  and rigid and the filling of the  ventricle is impaired . The commonest cause for diastolic dysfunction are  hypertension, diabetes, and  ischemic  CAD some forms of myopathies  .In systole ,the calcium  is pumped into actin myosin complex  while in diastole the  same calcium molecules  (Or different !)   are ejected back into the cytosol and sarcoplasmic reticulum. The later process is impaired in many situations of diastolic dysfunction.

It should  also be realised not every one with diastolic dysfunction  has a  calcium release /unloading defect .Many  have structural diastolic dysfunction  like interstitial fibrosis  .Here the mechanism goes beyond  calcium kinetics.These are the patients who get maximum  benefit out of heart rate reduction.

It is all Time  . . . Time as a  lusiotropic  drug !

If the ventricle finds difficult to relax  (or slow /sluggish to relax )  we have  two  options to tackle this .

  • To make relaxation  faster( ie positive lusiotropism )*
  • To  prolong the diastole  itself  .

Prolonging diastole makes it certain , the LV relaxation process is completed   as the excess time compensates for  the slowness of calcium reuptake into the sarcoplasmic reticulum . In fact , we have observed at slow heart rates (<60)  it is very difficult to document diastolic dysfunction  by doppler .

In many of  dilated  cardiomyopathies  the beneficial effect of  beta blockers , could be linked to simple reduction in heart rate and prolongation of diastole .(Note In DCM about 30-40 % have restrictive filling )

Final message

As we have no specific drugs to  augment the  process  of   cardiac diastole,  currently heart rate reduction  could be the simple and best method*  to improve diastolic function  .In many cases  diastolic dysfunction  simply vanishes  at low heart rate.Bradycardia  and  diastolic dysfunction   will remain as foes  forever !  Please give the benefit of this simple concept to all your patients with diastolic dysfunction .Your patients  can breath lot more easier !

*Apart from controlling the underlying cause like DM, SHT and CAD  , anti fibrotic drugs,  interstitial relaxants ,selective cardiac   collagen uncouplers  are the  future areas of research .

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