Wednesday, 7 December 2016

ECG of the Week - 5th December 2016 - Interpretation

The following ECG is from a 57 yr old male who presented with diarrhoea & vomiting. Past medical history of T2DM and  hypertension. The second ECG is from a month prior when the patient had presented with epigastric pain.

ECG during acute presentation
Click to enlarge
Key features:
  • Regular ventricular rhythm
  • Ventricular rate 96 bpm
  • QRS Morphology same as prior ECG - see below
  • Notching in terminal portion of T wave
    • Best seen leads II, III
  • QT 400ms (QTC 515ms)
  • ? Due to superimposition of p wave in terminal QRS

ECG From 1 Month Prior
Click to enlarge
Key features:
  • Regular sinus rhythm
  • Rate 84 bpm
  • Normal / inferior axis
  • Marked 1st degree AV block 
  • PR interval 320ms
  • QT 350 (QTc 420ms)
The debate

These ECG's have divided opinion regarding the rhythm of the first 'acute' ECG and I have to admit that I don't have a conclusive answer. 

There are two major thoughts:

  1. Sinus rhythm with the P wave superimposed in the T wave due to PR prolongation
  2. Accelerated junctional rhythm

I'm waiting on the opinion of our blog's electrophysiologists to hopefully settle the debate and I'll update the post once I hear off them.

In addition the patient's point of care electrolytes were normal.

The second ECG is relatively straight forward and we've covered marked 1st degree AV block before, but here's a refresher.

There are multiple potential causes of PR prolongation including:
  • Ischaemia 
  • Athletic heart
  • Increased vagal tone
  • Electrolyte disturbance
  • Myocarditis
  • Drugs
  • Valvular disease
  • LV Dysfunction
  • Hypothermia
In this case our patient has marked PR prolongation, defined as PR >300ms, which has the potential to cause symptoms. Symptomatic marked 1st degree AV block is a clinical situation similar to Pacemaker Syndrome. Symptoms are due to AV dyssynchrony and retrograde ventriculoatrial conduction. Cardiac output may be compromised as marked PR prolongation can have effects on cardiac function, including:
  • Atrial contraction before complete atrial filing
  • Compromised ventricular filling
  • Increased pulmonary capillary wedge pressure
  • Decreased cardiac output
Whilst treatment of symptomatic marked 1st degree AV block should initially focus on treatment and correction of underlying cause pacemaker insertion may be considered. 

The following are excerpts from the AHA 2008 'Guidelines for Device-based Therapy of Cardiac Rhythm Abnormalities' concerning 1st degree AV block:
  • Class IIa Recommendation
    • Permanent pacemaker implantation is reasonable for first or second-degree AV block with symptoms similar to those of pacemaker syndrome or haemodynamic compromise.(Level of Evidence: B) 
  • Class III Recommendation
    • Permanent pacemaker implantation is not indicated for asymptomatic first-degree AV block. (Level of Evidence: B)
Is it as benign as we think it is ?

1st degree AV block is usually considered a benign clinical entity with little to no effect on patient morbidity and mortality. 
I've included links in the reference section to some interesting papers looking at 1st degree AV block in patients with heart disease, older age groups, and a review article of 1st degree AV block. I'll let are interested readers go through these articles themselves, but in brief:
  • Cheng et al, This article was published in JAMA in 2009. Prospective cohort study using data from patients enrolled in the Framingham Heart Study.. Of the total study group, n=7575, 124 (1.6%) patients had 1st degree AV block. Those patients with 1st degree AV block had increased risks of atrial fibrillation, pacemaker implantation, and death.
  • Crisel et al. This article was published in European Heart Journal in 2011. Prospective cohort study of patients with stable coronary artery disease from the Heart and Soul Study. Of the total study group, n=938, 87 (9.3%) patients had 1st degree AV block.  Over a mean follow-up of 6.2 years the group with 1st degree AV block had increased risk of hospitalisation for heart failure, cardiovascular death, and all-cause mortality.
  • Holmqvist et al. A new review article, May 2013, from the Annals of Noninvasive Electrocardiology. This paper covers the available evidence for the implications of 1st degree AV block in a number of patient groups including young healthy people, community populations, coronary heart disease, and congestive cardiac failure. The authors conclude that 1st degree AV block is not entirely benign but pose the interesting question as to whether 1st degree AV block helps us identify high risk patients or represents part of the pathological problem ?
I will point out that I haven't attempted to critically appraise the above articles, but I would encourage our readers to look at the papers, and draw their own conclusions.

References / Further Reading

Life in the Fast Lane

  • Accelerated junctional rhythm
  • 1st Degree AV Block 
  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.

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