Dr.S.Venkatesan MD

A combination of  low voltage  qrs  and high voltage  qrs is a well known marker of dilated cardiomyopathy . classically patients with  severe forms  of  dilated cardiomyopathy show high voltage qrs complex in V1 to V6 and significantly low voltage in limb leads.

Why this happens ?

This happens due to two reasons.

1 .We know , chest leads are unipolar and picks up the electrical activity directly beneath the lead. In dilated  cardiomyopathy the enlarged heart (Usually more than 6 cm in diastole , may reach 9cm ) brings the myocardium closer to chest .This increases the electromotive forces reaching the lead.

2. The enlarged LV increases the  residual  end systolic and  end diastolic  volume , this increase in blood volume independently increases the electrical  conductivity and inscribes a high voltage complex.

This is some  times called as Brody effect .The same phenomenon occurs  in physiological conditions  as in stress testing  where excercise increases the qrs voltage due to increased

Why  limb leads do not show this high voltage ?

The limb leads are bi polar leads  hence as a rule , they record a smaller voltage than chest leads.In many patients with cardiomyopathy , the muscle mass  is  replaced by fibrotic tissue (Interstitial fibrosis ) and this brings down the net electrical energy draining from the heart.

Note : In spite of this, a dilated LV  records high voltage in precardial leads as explained above

When can limb leads  record high voltage in cardiomyopathy ?

It should be realised conduction defects can cause an increase in qrs voltage irrespective of the status of the muscle .This happens due to LAFB,LBBB, non specific IVCD. Because  , these conduction defects are very common in cardiomyopathy ,  there is very poor correlation of LV mass verses  high  voltage  qrs .

What is the correlation of low voltage to LV muscle mass ?

This has better correlation a very poor voltage < 5 mm( the largest qrs ) in the limb leads  predicts a very badly scarred LV .