ECG of the Week - 29th July 2013 - Interpretation

This ECG is from a 49yr old who presented complaining of palpitations and feeling lightheaded.
On multiple medications including amiodarone, ACE-inhibitor, digoxin, and a beta-blocker.
Hx of cardiomyopathy with AICD in situ.

Check out the original post of this case including a number of excellent comments here.

Click to enlarge

Rate:

• Ventricular rate ~120 bpm

Rhythm:

• Regular rhythm

Axis:

• LAD (-60 deg)

Intervals:

• PR - nil p wave seen
• QRS - Prolonged (160ms)
• QT - 440ms (QTc Bazette ~ 610 ms)

Segments:

• ST depression V2 - up-sloping
• Subtle ST depression V6

Additional:

• T wave inversion leads I, aVL
• Pacing spikes noted
• Apex of alternate QRS complexes
• Cycle length 1000ms (60 bpm)
• No evidence of capture associated with spikes
• Nil concordance
• No fusion / capture beats

Interpretation:

• Broad complex tachyarrhythmia
• DDx:
• Ventricular Tachycardia
• Hyperkalaemia
• Drug toxicity
• Pacing signal with:
• Failure to sense
• Failure to capture
• Failure of anti-tachycardia / shock sensing

What happened ?

The patient had normal electrolyte profile without evidence of drug toxicity.
Pacemaker was reprogrammed with subsequent resolution of the 'slow' VT.

Comments & Questions

We had a great selection of comments and questions from this week's case, including:

• The signals themselves are simply not being sensed by the device. If they were being sensed, the pacing spikes would be inhibited. Under-sensing could  possibly be related to the slow rise time of the signals in VT.
• Can anyone explain why the ICD doesn't defibrillate? Is it because the rate is "too slow" for a regular VT?
• Could it be that the rise time (frequency) of the signal is slow that it is outside the sensing frequency range? Combo of cardiomyopathy and amio?

I have forwarded these questions to the blog team cardiologists and I will update this post when I hear back from them.


VAQ Corner

A 49 year old presents to your Emergency Department complaining of palpitations and feeling lightheaded.
Vital signs: BP 106/52, RR16, Sats 98% on room air, afebrile.
On multiple medications including amiodarone, ACE-inhibitor, digoxin, and a beta-blocker.
Hx of cardiomyopathy with AICD in situ.
An ECG is performed - see above

Describe and interpret the ECG (100%)

References / Further Reading

Life in the Fast Lane

• Pacemaker Function Overview here
• Pacemaker Related Problems here

Textbook

• Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.