Feeds:
Posts
Comments

Posts Tagged ‘cardiac reserve’

LV dysfunction is one of the most commonly used terminology by cardiac professionals.It can be systolic, diastolic or global, regional etc. But, before dysfunction sets in, the heart fights. The Left ventricle can behave in many different ways when confronted with stress. It increases the force of contraction, elevates it’s Intra cavitary filling pressure and still accomplishes its task of pumping adequately. Further, It can build fresh muscle (LVH). It can double up with more heartbeats. (All these factors are referred to as cardiac reserve mechanisms)

These reserve mechanisms can be activated in the short or long term. In the long term, autonomic activation with neuroendocrine factors joins the compensation process.  These will work for some time till the circulatory system settles down to new homeostasis. However, they become counterproductive and becomes decompensated, ultimately heart failure sets in(Unless Intervened)

 

Is LV dilatation a mechanism of cardiac reserve ?

No one calls LV dilatation as a reserve or compensatory mechanism. (I wonder, why not ?) I think like RV ,  LV too has some potential to reversibly dilate . The quantum of which we are unable to estimate.This happens usually in response to chronic  volume stress* like regurgitant valves or high output states. Though cardiomegaly and a huge heart convey a sinister outcome, many hearts shrink if the primary issue is corrected.(Typically in Anemia, Beri Berri. We also know LV may transiently dilate in response to some toxic /pregnancy-related cardiomyopathy.

* Mind you LV poorly tolerates acute volume stress as in Acute AR/MR

The critical gap in our understanding is about this question.

When does LV dilate physiologically and when pathological persistent LV dilation sets in (The absolute state of irreversibly lost cardiac elasticity.) We also know dilated LV will consume more oxygen due to enhanced wall stress (Laplace law) and hence its possible LV dilatation begets further dilatation. Optimal timing of mitral and aortic valve replacement in patients with AR and MR directly depend on this knowledge.

Final message

We need clarity in the following queries

  • Is LV dilatation (with normal EF ) a sign of LV dysfunction?
  • If so at what level of dilatation?
  • Since LV dilatation  occurs in diastole can we fit this entity “Isolated LV dilatation” in the already confused spectrum of diastolic dysfunction?

Let us wait for the knowledge to evolve. Young cardiologists could take up this area for research.

Read Full Post »

Left ventricular hypertrophy is one of the most common clinical cardiac entity.It is recognised either by ECG or echocardiography.LVH has a unique place in cardiology as it can imply a  grossly pathological state  or  a marker of healthy heart as in physiological hypertrophy in athletes.

Logic would suggest , in this era of  stem cells and  nano medicine ,  every muscle fibre in ventricle is worth in gold !. So when the nature provides an  extra reserve of myocardium in the form of LVH one should welcome it , if otherwise not harmful.

Is LVH due to systemic hypertension benign ?

Not really, LVH has been shown to be an independent cardiac risk factor. (The famous Framingham study)Further LVH can result in diastolic dysfunction and the risk of cardiac failure increases.

But in spite of these observations, an  astute clinician with considerable experience will appreciate , patients with LVH fare better during an acute coronary syndrome !

This has been a consistent clinical observation . (Shall we call it as class C . ACC /AHA evidence ? )

Is LVH  an asset during ACS ?

  • A hypertrophied heart takes ischemic injury very easy , it doesn’t really hurt much . Another possibility is that in  LVH myocytes are relatively resistant to hypoxia .
  • Patients with LVH rarely show  significant wall motion defect following an STEMI.This is probably because the full thickness transmural necrosis is almost never possible even if extensive MI occurs.
  • This is also reflected in ECG  as these patients   rarely develop q waves in  following STEMI .
  • Persistent ST elevation and failed thrombolysis is very uncommon in pateints with LVH.
  • LVH provides  a relative immunity against development of cardiogenic shock . It requires 40% of LV mass destruction to produce cardiogenic shock.This can rarely happen in LVH. In a  long term analysis we have found none of the patient with LVH developed cardiogenic shock following STEMI.
  • LVH patients  are also protected against development of free wall rupture.

 Concluding message

“Lack of evidence  does not make a fact , a myth”

LVH , either pathological or physiological , has a hither to unreported beneficial effect .It acts as a myocardial  reserve and help limit the impact of STEMI .

Read Full Post »