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Posts Tagged ‘concentric lvh’

LVH is one of the commonest ECG abnormality . We know the hall mark  of LVH is increased QRS voltage .We also know , ECG is not a fool proof method to detect LVH .It has very good specificity , but little sensitivity , meaning that increase in  QRS voltage is  fairly accurate in predicting LVH  but absence of  which cannot exclude LVH.

Why Increased QRS voltage does not occur in many with LVH ?

Even though we think myocardial mass  is  the  sole determinant of QRS  voltage  , in reality  it   is determined by many other factors.

  • Distance between the ECG lead , and the myocardium is an important factor. In classical concentric LVH , the LV  cavity is not enlarged ,in fact it may shrink a little as the hypertrophy grow inwards and obliterate the LV cavity.(We do not know yet , how much of LVH grow out and how much  muscle grow in ! )
  • The blood volume within LV is a very good conductor of electricity.A good volumed LV may augment a QRS voltage.
  • This can be observed in some of the patients with DCM , where high voltage QRS  is recorded mimicking LVH.

But ,what really matters is the fine balance of blood volume and myocardial mass that determine the incidence and magnitude of LVH pattern in ECG.

QRS voltage as a tool to differentiate pathological from physiological  LVH

We know QRS current is generated from within the myocytes .If the myocytes  are  uniformly hypertrophy without altering the  basic mechanical and electrical architecture QRS complex will be amplified in a sm0oth manner and result in  classical high voltage  QRS  of LVH.

If the hypertrophy occurs in a disorganised fashion, where in myocardial fibres slips out of plane  with adjacent muscle bundles, the QRS  voltage may not increase and even be slurred or notched as we see in many cases of LVH with non specific intravascular conduction defects

The classical disarray of myocardial fibers that occur in HCM causes  pathological q waves.

* Other factors that determine LVH include bundle branch conduction delay or blocks which is not discussed here.(Ex: An incomplete LBBB can amplify the qrs without any LVH )

LVH with fibrosis

Fibrosis is not a standard feature of LVH. It occurs in few who are genetically predisposed , and  mediated by heightened sensitivity to circulating growth factors.

  • Fibrosis can have wide impact on the electrical as well as mechanical function of heart.
  • Fibrotic heart has a  potential to  blunt the  high voltage  QRS complex.
  • It  may even cause  pathological q waves .It predispose to ventricular arrhythmia
  • It prevents regression of LVH , even after the loading conditions corrected.

Other conditions that  attenuate LVH features in ECG

  • Diabetic hypertensive show less ECG voltage than isolated HT .
  • CKD patients often do not show ECG features of LVH inspite of LVH

Final message

Diagnosis  of  LVH by ECG is a  simple clinical exercise , but we realise now , the underlying mechanisms are too complex .

A simple question , ie  Why  every one  with LVH  do not increase  their  QRS voltage  ?  . . . exposes  our ignorance on the subject!

But one thing is clear, physiological LVH (Meaning LVH ,  purely due to loading conditions including SHT/Aortic stenosis)  more often result in high voltage , while  in true pathological LVH(infested with fibrosis ) the  increase in voltage is not consistent .

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ECG of an athlete is many times difficult to interpret. The influence of autonomic tone in  athlete’s heart is an complex one.Contrary to our expectations the parasympathetic tone is higher in well trained athletes. The resting heart rate can be as low as 30/mt which is 99.9 times pathological in non athletes.This happens due to a concept called accentuated antagonism.The athletes who have episodic surge of high catecholamines keep stimulating the para sympathetic neurones in a constant fashion.

LVH is the most common feature.Here there is simple myocyte hypertrophy, without pathological fibrosis.This differentiates athlete’s, heart from HOCM .

Many ECG abnormalities are reported in athletes.

Excerpts from the ACC recommendation

1. Electrocardiographic findings that are common and training-related and that do not require additional evaluation are sinus bradycardia, 1° atrioventricular block (AVB), incomplete right bundle branch block (BBB), early repolarization, and isolated voltage criteria for left ventricular hypertrophy (LVH).

2. Uncommon and training unrelated electrocardiographic findings that mandate further evaluation include T-wave inversion, ST-segment depression, pathological Q waves, atrial enlargement, a hemiblock, right ventricular hypertrophy, a BBB, or a Brugada-pattern of ST-segment elevation.

3. Training-related electrocardiographic findings are more common in men than women, athletes of African descent, and high-endurance athletes such as cyclists.

4. Sinus rates <30 bpm and sinus pauses >2 seconds are common in highly trained athletes, particularly during sleep.

5. A normal chronotropic response to exertion and the absence of bradycardia-related symptoms distinguishes training-related sinus bradycardia from sinus node dysfunction.

6. 1° AVB and Mobitz I 2° AVB are common, but Mobitz II 2° AVB or 3° AVB should not be assumed to be training-related and require evaluation.

7. Early repolarization in Caucasian athletes most commonly consists of upwardly concave ST-segments and tall and peaked T waves; in black athletes, there often is convex ST-segment elevation and negative T waves, mimicking a Brugada pattern.

8. In the presence of voltage criteria for LVH, pathological hypertrophy should be suspected if there is left atrial enlargement, left-axis deviation, repolarization abnormalities, or pathological Q waves.

9. T-wave inversion ≥2 mm in ≥2 adjacent leads should prompt evaluation for structural heart disease.

10. Electrophysiological testing for risk stratification with possible catheter ablation is appropriate in athletes with ventricular pre-excitation.

Source :  Fred Morady, M.D., F.A.C.C.

http://www.ncbi.nlm.nih.gov/pubmed/19933514?dopt=Abstract

For an excellent article on the topic click here

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