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Posts Tagged ‘wiggers cardiac cycle’

Ventricular pressure volume loop is an Important ( often feared !) concept to learn for cardiology fellows . . . I would say , It is not that hard to understand !

These loops tell us the secret  hemodynamic story of a 300 gram “mass of muscle” called the heart  and how It handles about 100 ml of blood every beat and successfully ejects around 70 ml into Aorta and Pulmonary artery *

108356heart_beating

While doing this life sustaining job , It would seem the heart muscle  conducts a perfect, non stop, hemodynamic orchestra with 4 electro-mechanically coupled phases which is depicted as classical ventricular pressure volume  loop. Mind you, this loop is plotted pressure volume data from a single heart beat and it can’t be time correlated with heart sounds or ECG as the two parameters loop around in same time cycle.

Watch this animation , carefully and read the appearing annotation that come along with each phase.That should suffice to understand the basic. (For Audio version go the video link in the reference )

Modified from a clipping from Giphy.com.Original source of this Image is not located. Whoever has done this thanks and it’s a great attempt.(I have tried a fusion Image of doppler mitral Inflow in diastole and Aortic pressure curve during ssytole to bring PV loop an anatomical perspective.)

*Note: When we say PV loop it means about by LV by default . We do have seperate RV ,LA (even RA?) PV loops.

Is there clinical application for  PV loops ?

It may not have any direct use , but understanding  how a ventricle works in normal conditions or at distress especially during acute decompensations or after surgery  is vital. With modern gadgets like LV assist devices,  Impella used widely and to assess hemodynamic efficiency of transplanted (Very soon total artificial hearts) , PV loop analysis of both RV/LV will be critical.

Is there any simple Lab modality that can draw this Loop curve instantaneously ?

echocardiography lab methods for ventricular pressure volume loop

 

Very few companies make it . AdInstruments that make power lab monitors, enable us to visualise PV loops invasively .

 

Can we get PV loops non invasively by Echocardiography ?

Echocardiography  provide us both volume  and pressure data.With improving accuracy of data it should be possible to plot the loop manually with some effort. (Still , we can’t get pressure in all points of cardiac cycle )

I guess, sooner 3D volumetric machines with automated online doppler pressure data across the valves  can help us draw the ultimate LV functional  curve live on real time.If that happens cardiologists will be further enriched and hemodynamically enlightened !

Final message

The shape , size , timing and the slopes of this loop  givs us vital info about the functional aspects of ventricle. First one should understand the normal loop , then , we can dwell on the effects of acute and chronic lesions like regurgitations, cardiomyopathy ,cardiogenic shock etc.

Reference 

An excellent knwoledge base on the topic with a  video 

Dr. Richard E. Klabunde, PhD

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The mechanical atrial function   during atrial fibrillation remain a mystery . In fact , the general  belief  is during  AF  the mechanical function of atria is zero. This is why AF  is promotes stasis and   LA clot formation. It may appear theoretically correct  , still   AF especially coarse  still imparts some amount of  mechanical motion .But this usually does not translate to any useful hemodynamic function .

If atrial booster pump is lost (which is said to be 25 % of  LV filling )  suddenly one expects dramatic symptoms  especially if there is associated LV dysfunction or aortic valve disease .

But in real world AF is well tolerated arrhythmia in most  .  We know by land  mark trials AF  is as good as sinus rhythm  if the rate is  is under control

This is a definite evidence the AF  may not compromise  LV filling   even if   it nullifies  the  atrial contractility .

There is one  more evidence for  retention of atrial mechanical activity in spite of AF .It is well recognised , pre-systolic accentuation is preserved  in many cases of mitral stenosis with AF.

*Crazy hemodynamics : For an attached LA clot to  dislodge ,   one needs some amount of LA contraction isn’t ?  Unfortunately  a fibrillating  atria always  tend to  have this one ! This again is a senseless  proof for some  mechanical activity of LA during AF !

How is this possible ?

Is it a  purely volume dependent filling   ? ( Or )  is it  the  Intrinsic LA starling forces that do not depend electrical atrial activation .

This is definitely an  issue to ponder over . A good LV contraction makes the atria empty more completely . This would  somehow  mean , LV relaxation  is facilitating atrial function . During  AF the LV  handles effectively  the additional burden  imposed by the loss of   25  %  booster pump of atria ( Accelerated LV relaxation ? )  A  constantly  changing  RR interval makes LV diastolic function a more complex event .

Final message

Atrial fibrillation is  a well tolerated  arrhythmia in vast  majority of patients  . This  implies either of the two things.

  1. The so called  physiological atrial  booster pump is redundant  or dispensable in otherwise healthy heart
  2. The booster pump is indeed important  . . . but it is less  affected by AF as long as the rate is under control !

It is to be  strongly emphasized , Heart rate and  LV function  will ultimately determine  , how one is going to tolerate the AF  !

It is  a small gesture  from LV  to LA  at it’s hour of crisis  . . . in return  for  it’s lifetime assistance  as a booster pump ! 

Postamble

How  rate control  prevails over rhythm control in spite  zero atrial contractility in the  former  ?

Comments welcome !

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