Wednesday, 21 August 2013

ECG of the Week - 19th August 2013 - Interpretation

Again unfortunately no clinical information on this case, but that's never stopped us before.
Check out the comments on our original case post here. 






Click to enlarge
Rate:
  • ~69 bpm
Rhythm:
  • Regular
Axis:
  • Normal (30 deg)
Intervals:
  • PR - Prolonged (~420ms)
  • QRS - Normal (80ms)
  • QT - 440ms (QTc Bazette ~ 470 ms)
Additional:

  • T flattening leads III, aVL
  • Notched P wave lead II
  • rSr' QRS pattern leads aVR, V1

Interpretation:

  • Marked PR prolongation
    • PR >300ms
  • Non-specific T wave flattening
I don't have any further clinical information regarding the case specifics or the clinical outcome.

1st Degree AV Block

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.

VAQ Corner

A 57 yr old female presents to the Emergency Department she complains of 2 days of atypical chest pain. She is normally fit & well. She takes no medication.
Her ECG is above.

a) Describe and interpret (100%)

References / Further Reading

Articles

  • Crisel RK, Farzaneh-Far R, Na B, Whooley MA. First-degree atrioventricular block is associated with heart failure and death in persons with stable coronary artery disease: data from the Heart and Soul Study. Eur Heart J. 2011 Aug;32(15):1875-80. PMID: 21606074  Full Text Here
  • Cheng S, Keyes MJ, Larson MG, McCabe EL, Newton-Cheh C, Levy D, Benjamin EJ, Vasan RS, Wang TJ. Long-term outcomes in individuals with prolonged PR interval or first-degree atrioventricular block. JAMA. 2009 Jun 24;301(24):2571-7. PMID: 19549974   Full Text Here
  • Holmqvist F, Daubert JPFirst-degree AV block-an entirely benign finding or a potentially curable cause of cardiac disease? Ann Noninvasive Electrocardiol. 2013 May;18(3):215-24. PMID: 23714079
  • Epstein AE, Dimarco JP, Ellenbogen KA, Estes NA 3rd, Freedman RA, Gettes LS, Gillinov AM, Gregoratos G, Hammill SC, Hayes DL, Hlatky MA, Newby LK,Page RL, Schoenfeld MH, Silka MJ, Stevenson LW, Sweeney MO; American College of Cardiology; American Heart Association Task Force on Practice Guidelines; American Association for Thoracic Surgery; Society of Thoracic Surgeons. ACC/AHA/HRS 2008 Guidelines for device-based therapy of cardiac rhythm abnormalities. Heart Rhythm. 2008 Jun;5(6):e1-62. PMID: 18534360  Full text here
Life in the Fast Lane
  • 1st Degree AV Block here
Textbook
  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.