Like it? Share it!

Monday, 25 February 2013

First Degree Heart Block


Discussion

#ECGclass case 25.

A 72yr old lady comes to see you complaining of mild fatigue, and occasional shortness of breath. She finds her house-work a little more tiring than she used too. She laughs as she tells you that her family say she just  "does too much" and "doesn't recognise that she needs to slow down".  She thinks they may be right, but just wanted your opinion and a check up.

She denies any chest discomfort during these episodes.
She has no past history of, or risk factors for, IHD other than her long standing hypertension.

Her BP has been well controlled for many years on Atenolol 50mg.  On the basis of more recent evidence, and hypertension guidelines, you discussed with her the pros and cons of changing this at her last medication review, but she was keen not to 'meddle', as it suited her well.

Respiratory and Cardiovascular examination are normal.
In particular, she has no creps, no ankle swelling, and no murmurs.
She is of slim build and looks clinically well.

You decide to check her ECG and BNP.
Other bloods (including FBC, U&E's, eGFR and TFTs) were all done within the last 3months and were all normal.

Her BNP comes back at 56 pg/ml and her ECG is below:


Q1.  What do you think of the machine analysis "Normal Sinus Rhythm"?

        Remember the definition of Normal Sinus Rhythm ?

        Regular QRS complexes. (Rate around 60bpm) - yes
        Regular P waves - yes
        P waves upright and positive in the inferior leads - yes
        Every P wave is followed by a QRS - yes
        The PR interval is constant, and < 0.02 sec  -  no. 
           

Q2.  What do you think of the machine analysis "Anteroseptal infarct, probably old" ?
       Less certain here. It's the Q-waves in V1 and V2 that the machine is getting excited about. Not      very convincing, but possible I suppose. (see Pathological Q waves). I suspect these are non-pathological Q waves, but we could do we a closer look, to exclude a small R wave preceding them, like the one we start to see in V3.

Q3.  Is there any voltage criteria LVH? 
     No. None convincing.  See Voltage criteria for LVH if you need refreshing.

Q4.  What is the PR interval?
    Aha. Now we're talking. For ease of measurement, look on the long lead two and choose a complex where the start point of the p-wave sits just nicely on a 5mm marking.  On this ECG that's the P wave before either the 4th (or 8th) QRS complex. It looks about 12 small squares to me? That is  12 x0.04sec = 0.48 seconds. (Normal range is 3-5 small squares, or 0.11- 0.20 seconds).
The PR interval is long. This is First Degree Heart Block

Q5.  What action might you take next?
Common causes of First degree Heart block include 

  • AV nodal disease
  • Enhanced vagal tone (athletes)
  • Myocarditis
  • Acute Myocardial Infarction (commonly Acute Inferior MI)
  • Electrolyte disturbances
  • Medication (rate limiting calcium channel blockers, beta-blockers, cardiac glycosides)

Most of these causes can be excluded in the history above, apart from medication (and AV nodal disease). 

This lady needs her beta-blocker stopping. 

If she needs an alternative treatment for BP control, then treat in accordance with current Hypertension guidelines (e.g. Consider a non-rate-limiting calcium antagonist, such as Amlodipine, or an ACE).

I suspect that a repeat ECG, just one week after stopping her beta-blocker, will be completely normal. You may just have prevented her from progressing to a more serious conductive system defect. 

In summary, I think her presenting symptoms are probably incidental. You may just want to exclude angina, by more detailed history taking and finding out more about her exercise tolerance and it's predictability, but her family are probably right in their assessment!  

First degree heart block is usually completely asymptomatic. 
However, her presentation has at least uncovered a potential future problem, which you can now pre-empt, and address. 

Thanks for taking part. :)






No comments:

Post a Comment