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Posts Tagged ‘myocardium’

The answer to this question  is not  easy  , as   one  would tend to believe . In fact this question , takes it for granted     revascularisation  will  improve the LV dysfunction in patients  with severe LV dysfunction.

The truth is , we  are not sure   about the mechanisms . How   revasculariastion  will have an effect  on  chronically dying or dead myocardium  ? (Acutely dying myocardium is a different story, where revascualrisation has a profound effect , that is called salvaging the myocardium )

This  issue is  of great clinical significance  in end stage ischemic heart disease  .A typical  myocardial segment in ischemic cardiomyopathy  has millions of  the dead cells  interwoven with dying cells  with  occasional  clusters if live cells scattered all over .Once the process of myocardial apotosis sets in ,  myocardial cell death does not result  in segmental destruction  instead  an universal cell death.(Paracrine signals of  cell death that spills over to adjacent segments  )  The current standards of revascualrisation (PCI and CABG) aims to provide blood flow  in a segmental fashion. Even if the blood flow is restored in an obstructive vessel it is not clear , how it is going to enter the chronically atrophied myocytes.

Meanwhile , many studies are available   suggesting  coronary revascularisation does indeed improve LV dysfunction. These  evidence has never been  conclusive .Real world experience would also  confirm this  simple fact , that   angina relief is definite following revascularisation but not dyspnea  relief  in patients  with LV dysfunction .

So ,  when seeking the  guidelines  for revascularisation  ( PCI or CABG )  in patients  with CAD one need to ask  this  specific  question

Does the patient has

A.Angina alone

B.Angina and dyspnea

C.Only  dyspnea

If the answer is C ,  assess the patient again , rule out systemic causes of dyspnea (Anemia, renal function etc)  rethink  or postpone  revascularisation.If primary  or secondary LV muscle dysfunction has set in revascularisation has little value.

Also read

Viable myocardium

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                                     Hypertension is considered a major cardiovascular risk factor.Hypertension  can have multiple physiological and pathological effects on heart . The common response to  raised arterial pressure is the hypertrophy of the left ventricle ( LVH). This can increase the risk of heart failure in few ( Mainly diastolic failure)  It is a leading cause for stroke  and   less often a  coronary event.

What links Hypertension and  coronary artery disease

                                           Coronary artery disease is almost synonymous with atherosclerosis. There is no separate entity called hypertensive coronary artery disease. But HT can accelerate the process of atherosclerosis. It is widely understood, hypertension can cause  physical endothelial damage and functional impairment of endothelial function.The physical damage ie enothelial disruption , or erosion is a very uncommon phenomenon . So currently  there is sufficient clinical experience  HT is considered dangerous for coronary artery only if it is with the  company of diabetes and hyperlipidemia. (This will seem controversial as it is against the findings of iconic Framingham trial!)

What the medical community refers to hypertension , may not be really so inside  for the coronary arteries.

                                             The relationship between brachial cuff blood pressure and the intra coronary pressure has very little linear relationship. So one should recognise it is the intra coronary hypertension that has a immediate impact on the coronary events. Now only , we are beginning to understand the complexities  of the relationship between HT and CAD. If we analyse a series of individuals HT per se is not a very serious risk factor for CAD* , but it is a number one risk factor for stroke. 

Why HT in isolation  often result in stroke , rather than a MI ?

While HT  is notoriously common to result  intracerebral hemorrhage, the same HT  would not cause  intramyocardial bleeds . Why ?

What is protecting the myocardium against this complication ?

                                      The exact mechanism  is not clear.Acute surges of blood pressure can increase the risk of stroke many times  but  rarely precipitate  a coronary event(  But may cause a LVF) . The reasons could be the coronary endothelial shearing stress is less than the cerebral blood vessels.Both cerebral and coronary circulation has  auto regulatory mechanism . The coronary auto regulation is more robust in that it does not allow  intra coronary pressures to reach critical levels .There is no clinically relevant intra myocardial hemorrhage reported  even during malignant hypertension.

*But a  high intra coronary pressure can sometimes  result in spontaneous coronary dissection and plaque fissure .Lipid mediated injury is vey much facilitated in a high pressure environment.

Has Controlling blood pressure  to optimal levels  , reduced the overall CAD morbidity and mortality ?

                    The answer is yes, ( But not an emphatic yes ! ) Some studies had been equivocal. It is very difficult to say , how much benefit is attributable to BP reduction  per se  and   how much is attributable to indirect effect on atherosclerosis prevention.

Hypertension during ACS

                            High blood pressure during an episode of unstable angina or STEMI can increase the myocardial oxygen demand and worsen the ischemia. It requires optimal control with nitroglycerine ( Preferably ) or beta blocker and ACE inhibitors.Even though HT is commonly associated  with ACS,  one can not be sure the ACS is preciptated by HT. Many times the sympathetic surge during an ACS keeps the blood pressure high.It is a common experience the blood pressure suddenly dropping to normal or hypotensive levels once the pain and anxiety is controlled.

Hypertension during thrombolysis

                           High blood pressure is a relative contraindication for thrombolysis.It need to be emphasised here, It is the  the fear of stroke that make  it contraindicated .The heart can tolerate  thrombolytic agents delivered at high BP .In fact logically ,  hemodynamically and also  practically it is obseved , thrombolytic agents administered at relatively high blood pressure (140-160 systolic) has better thrombolysis than a patient who is lysed at 100mmhg.

                       The coronary pressure head which contain the thrombolytic agent (streptokinase and others ) need to have pressure jet effect on the thrombus.So the  mean coronary perfusion pressure becomes  a critical determinant of success of thrombolysis.

                            It is a paradox of sorts , very high blood pressures are a relative contraindication for thrombolysis and at the same time normal pressure patients fare less well to thrombolysis.

 Final  message

                        Hypertension continues to be a major cardiovascular risk factor.It has direct and indirect effects on the heart.Generally HT is more of a risk factor for stroke than CAD.A slightly high BP ( Just around the  upper limits of normal or just above it ) has a hemodynamic advantage during thrombolysis.(Class C evidence )

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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 .

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The long standing controversy about diastolic heart failure is settled !

The perception that diastolic heart failure ( Now renamed as heart failure with preserved EF ) is less dangerous than systolic HF has been exposed by this land mark study by Owan TE, in 2006 (nejm) But unfortunately this information is not yet fully disseminated among the physician community. Hence this post, with due acknowledgment to NEJM & Owan et all.

Experts from the article

“The nosology of heart failure has been the
subject of much current debate, and some extreme
positions have been taken. The observation
that 22 to 29 percent of patients with diastolic
heart failure die within one year of hospital
discharge, and 65 percent die within five years,
is a reminder that we are facing a lethal condition,
regardless of its name. Owan et al. also
show that, in recent years, there has been little
improvement in survival rate among patients with
diastolic heart failure, in contrast to the improvement
in survival rate over time among patients
with systolic heart failure”

Have a look at the survival curve below, almost similar , surprise surprise ! DHF survival is not only worse ( in many ), than systolic CHF and further they respond poorly to treatment, compared to conventional systolic CHF .

Click below for the link to full text article

Short abstract :

Trends in prevalence and outcome of heart failure with preserved ejection fraction.

Cardiorenal Research Laboratory, Mayo Clinic College of Medicine, Rochester, Minn 55905, USA.

BACKGROUND: The prevalence of heart failure with preserved ejection fraction may be changing as a result of changes in population demographics and in the prevalence and treatment of risk factors for heart failure. Changes in the prevalence of heart failure with preserved ejection fraction may contribute to changes in the natural history of heart failure. We performed a study to define secular trends in the prevalence of heart failure with preserved ejection fraction among patients at a single institution over a 15-year period. METHODS: We studied all consecutive patients hospitalized with decompensated heart failure at Mayo Clinic Hospitals in Olmsted County, Minnesota, from 1987 through 2001. We classified patients as having either preserved or reduced ejection fraction. The patients were also classified as community patients (Olmsted County residents) or referral patients. Secular trends in the type of heart failure, associated cardiovascular disease, and survival were defined. RESULTS: A total of 6076 patients with heart failure were discharged over the 15-year period; data on ejection fraction were available for 4596 of these patients (76 percent). Of these, 53 percent had a reduced ejection fraction and 47 percent had a preserved ejection fraction. The proportion of patients with the diagnosis of heart failure with preserved ejection fraction increased over time and was significantly higher among community patients than among referral patients (55 percent vs. 45 percent). The prevalence rates of hypertension, atrial fibrillation, and diabetes among patients with heart failure increased significantly over time. Survival was slightly better among patients with preserved ejection fraction (adjusted hazard ratio for death, 0.96; P=0.01). Survival improved over time for those with reduced ejection fraction but not for those with preserved ejection fraction. CONCLUSIONS: The prevalence of heart failure with preserved ejection fraction increased over a 15-year period, while the rate of death from this disorder remained unchanged. These trends underscore the importance of this growing public health problem. Copyright 2006 Massachusetts Medical Society.

Other interesting article

Heart failure with preserved ejection fraction: dangerous, elusive, and difficult.

Eur Heart J. 2008 Feb;29(3):339-47. Nielsen OW, Køber L, Torp-Pedersen C.

BMJ editorail 2009

http://www.bmj.com/cgi/content/full/338/jan27_1/b52?ijkey=c7a29d35dc9d9dddf7d0e75c5b8d05014315c564

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Heart is a muscular pump .But it contains more of  non muscular cells than contractile cells.

The average human heart which weighs 300 -400 grams . Contrary  to the popular perception heart is not purely a muscular organ. In fact myocytes constitutes only 30% of heart mass. Rest formed by

1.Fibroblasts

2.Endothelial cells

3.Purkinje cells

4.Interstitial cells

5.Collagen

6.Fibrous skeleton

7.Extracellualr matrix.

Why is this important to recognise ?

Cardiac failure is not synonymous with myocardial failure .

Many times cardiac failure is due to supporting structure failure like in connective tissue disorders.

Exceesive fibroblast proliferation and resulting in fibrosis of heart.

Cardiac interstitial failure is new emerging clincal entity.

In future individual cell based therapy will aim  at replacing specific cells that are defective or depleting.

 

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