Q waves are neither sacred nor sinister waves . It represents either of the following .
- Electrical activity that goes away from the recording electrode.
- Or whenever there is a electrical insulation or hurdle that interrupts the flow of current towards the electrode ( and if it is sustained ) it can result in q waves (Minor interruption produces a notch or slurs . Please note a major slur becomes a q wave equivalent )
Here is young women of 42 years with a diagnosis of old anterior MI for over 5 years ( Getting a dedicated care from a cardiologist! The prescription included Imdur/Betaloc/ Statin/Clopidogrel and Aspirin )
This was the ECG . It was very convincing for old ASMI.
It happened , I did an echo for her .
She lacked wall motion defects even after a meticulous search . Instead she had a good layer of epicardial fat measuring 9 mm .That was more localised in anterior wall extending little to LV apex.Her EF 65 % .
*She was a fairly obese (not gross ) individual with a BMI of 34 .The fat pad thickness was not that huge , I thought , still it was producing the q waves . I have seen much thicker fat pads with good R waves in ECG . I wonder , is it the type of fat that adds up to electrical insulation ?
This patient was sent back to me again for ruling out ASMI . Echo was done two weeks later . No evidence for ASMI could be detected.
What is the normal thickness of epicardial fat pad ?
It is less than few mm . Exact normality is not known .(Empirically < 5mm ) it is very rare for fat deposition in infero posterior aspect , except in morbid obesity.
What is the function of epicardial fat ?
- Long considered inert . Now , found to be a metabolically active lipid pool.
- We also know heart consumes more fatty acid than an other organs for moment to moment energy consumption .
- Inflammatory mediator in atherosclerosis ?
- It may also act as a mechanical cushion effect along with pericardium
- Rarely fat infiltration can compress the heart and may result in restrictive AV filling defects in doppler .(May explain the unexpanded dyspnea in many obese patients )
Subcutaneous vs Epicardial fat.
We know thick chest wall can also interfere with ECG. Epicardial fat is more likely to record q waves than sub cutaneous fat , as the insulation is more closer to heart in epicardial fat . In thick chest wall current leaks from heart and well scattered hence poor R wave is more common in such situations rather than q waves !
Following things can generate q waves (Other than Infarct )
- Fibrosis-Myocardial /Interstitial
- Thickened pericardium
- Thick chest wall/ Epicardial fat
- Air/Fluid in pericardial space
In obese men and women anterior Q wave can be misleading .Such medical errors can be so convincing .
If epicardial fat can extinguish R waves and replace it with q waves , these innocuous looking fat pads has every reason to influence the ST segment shifts during an episode of ACS as well ! . Isn’t ? . If so . . . how reliable is our ECG criterias to diagnose acute coronary syndromes in grossly obese men and women ?