Posts Tagged ‘cardiomegaly’

By statistics cardiomegaly   often implies  ventricular enlargement (especially left ventricular) .Right ventricle generally do not enlarge the  CT ratio until late stages .

More important  is the impact of right atrial enlargement on the CT ratio. Here was a  patient referred to echo lab for evaluation of cardiomegaly

The x-ray chest  was suggesting a definite LV enlargement.  To my surprise  the LV was perfectly  measuring a normal dimension .

The right atrium was huge and measuring  more than 5 cms . This increased the CTR.

The following illustration  tries to create echo equivalent of transverse CT diameter by rotating apical 4 chamber view by 90 degrees.

The right and left atrium was significantly dilated . This patient had atrial fibrillation and the atrial enlargement was due to chronic AF.

Final message

Cardimegaly in  X- ray chest do not  necessarily  mean ventricular enlargement.

Pure atrio-megaly  especially right atrial enlargement can dramatically increase the CT ratio.

This is not a big  discovery , still fellows need   to reinforce  this fact  , as  mistakes are most often committed in well  known things !

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Let ventricle is an elliptical or ovoid chamber .The pattern of LV enlargement can vary considerably in different pathologies. We know a dilated , globular heart is the typical feature of terminal congestive heart failure. But in the early stages of cadiac enlargement there are some distinct differences in the contour. (Aortic stenotic lesions retain the ellipitical shape till late in the course )

LV enlargement due to mitral regurgitation is somewhat different from aortic regurgitation. A globular configuration occurs more often in severe MR than AR. This is due to the fact, the long axis and short axis ratio of LV  is maintained till late in the course  of aortic valve disease . Cardiac long axis enlargement is more pronounced in aortic valve disease than in MR. The AR jet reaches LV  at a higher pressure gradient (Diastolic pressure of aorta) than mitral inflow velocity . (Often mimic physiological flow with an S3)

For a given degree of regurgitant volume AR will cause more cardiac enlargement than MR. In the same note , one should realise  the LA becomes huge in MR which receives high pressure regurgitant jet . Further ,mitral valve disease is more likely to result in early PAH and that results in right sided chamber enlargement giving the cardiac contour a more globular configuration

Is the cardiac contour different in rheumatic and degenerative(Myxamatous) mitral regurgitation ?

Yes , rheumatic MR results in less enlargement of the base of the heart as the fibrotic process restricts and restrains LV and prevents uncontrolled LV dilatation . In fact , giant LV are often  reported in mitral regurgitation due to mitral valve prolapse than rheumatic MR.

Why the configuration of LV important in the management of cadiac failure ?

The globular configuration of LV implies , the papillary muscles are attached in a disadvantaged angle and keep the free wall stress high. Specialized procedures are required to restore the LV shape especially in secondary to mitral annular dilatation. Isolated aortic valve disease rarely require LV remodeling surgeries , even if AVR is done late stages.

What is the maximum dimension of LV reported in cardiac failure ?

The upper limit of normal for LV diastolic dimension is 5.6cms. In MR it often reaches 6-7 cms . The maximum of 10cm has been reported with AR. An LV beyond this level looses it’s elasticity and likely to be incompatible with survival unless LV reduction surgeries like Batista are performed.

Is secondary valvular cardiomyopathy an accepted entity ?

 The  term cardiomyopathy when originally defined decades ago ,  required exclusion of all known cases of cardiac enlargement. But now we have a more liberal working concept , if the LV enlarges disproportionate to the loading conditions of the valvular lesions  , secondary cardiomyopathy is said to be present. If cadiomyopathy sets in,  the cardiac shape invariably takes in a globular configuration irrespective of the valvular lesions. So, the simple parameter of shape of LV in X ray chest can give us a clue regarding the outcome in valvular heart disease.

Further reading

Also read sphericity index by echocardiography A spherical LV can be easily quantified by echocardiography

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Thorax is a rigid bony  box  with a fixed space.The intra thoracic organs are snugly  arranged  within the cavity.The two lungs on either side with the heart in the middle fill the major volume of the mediastinum .In  physiological conditions the volume of mediastinum remain almost constant , except for the respiratory swings.

heart lungs pulmonary function test dyspnea cardiomegaly ct ratio

It is to be noted the two major organs inside the thorax has a distinct behavioral pattern.  Lung  a very pressure sensitive  structure tend to collapse   whenever confronted  with external pressure .This is evident in all cases of large pleural effusion (Note :The heart collapses only in a fraction of patients with  large pericardial effusion -ie tamponade) . Similarly in any mediastinal syndromes , first  the lung function is affected , logics then dictate ,  the  low pressure venous system to get compressed resulting in SVC /IVC syndrome.Finally the   right  heart chambers may get interfered with .This is due the  dynamic  intracardiac  pressures   that resists any compression from exterior.

So, it is obvious  ,  lung function is affected with raised intrathoracic volume or pressure .The increase in intrathoracic volume can be due to any thing .

cardiomegaly massive dyspnea mechanism lvedp

The volume of heart in cardiac failure can  increase very significantly .For a fraction  raise of CT ratio there is many fold raise in it’s volume.A CT ratio of 75% can cause a huge ” housing & accommodation ” problem for the lungs on either side . As we have discussed , the lung is  passive organ  has absolutely  no other option  but to bow down like a touch me not plant . The  lung , reduces it’s ventilatory   function impairing  the already poor exercise capacity .The terminal respiratory units collapse  significantly. This collapse is not visible in x rays as there is no intrinsic obstruction within the airways as happens in lung pathology.

The course of events in progressive cardiomegaly is often  silent and heart successfully encroaches the the human breathing space  until the heart failure is corrected and normal heart  size is restored. Complete reversal of heart size may not be possible always !

A new unrecognized mechanism for cardiac dyspnea ?

Yes,the mechanism of cardiac dyspnea always been  centered around elevated LVEDP , lung congestion etc and the resultant stimulation of lung receptors.

Now we realise  a reduction in the lung ventilatory  capacity  may also  contribute significantly in every patient with cardiac  failure and cardiomegaly.

When a person with single pnemonectomy lead a comfortable life what is the big issue of heart compressing few respiratory segments of a patient ?

It is true a single normally functioning lungs is sufficient for living but what we are dealing here is patients with compromised cardiac function.Recruitment or non recruitment  of even few  respiratory bronchooles may have a bearing on  patients symptoms and exercise capacity.

Final  message

Cardiomegaly  is not an  inert  consequence  of cardiac  failure. It can have important functional  impact on the pulmonary ventilatory  and perfusion capacity .It should be emphasised  this mechanical encroachment on the lung space is over and above the hemodynamic effects on pulmonary capillary circulation .

Youngsters  should recognise  this fact  as this offers  one more explanation for cardiac dyspnea. This is not often discussed in the clinical  classes.

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