ECG Blog #360 — The Patient has Cancer ...

The ECG in Figure-1 was obtained from an older woman. She presented with shortness of breath. The patient was known to have cancer. 

QUESTIONS:

• How would YOU interpret this ECG?
• Why is every-other-beat changing? 

Figure-1: ECG obtained from an older woman with shortness of breath. (To improve visualization — I've digitized the original ECG using PMcardio).

MY Thoughts on the ECG in Figure-1:

The ECG in Figure-1 — shows a regular, supraventricular (ie, narrow-QRS) rhythm at a rate of ~90-95/minute. All intervals (PR,QRS,QTc) and the frontal plane axis are normal. There is no chamber enlargement.  ST-T wave changes do not look acute.

There are 2 “eye-catching” features on the ECG in Figure-1:

• Diffuse Low Voltage: As discussed in detail in ECG Blog #272 — a series of clinical conditions have been associated with low voltage on ECG. Clinically — the entity of “low voltage” is defined by ECG criteria as the manifestation of a QRS amplitude of ≤5 mm in all 6 limb leads. This low voltage is said to be “diffuse” — IF — in addition to satisfying limb lead criteria, QRS amplitude in all 6 chest leads fails to exceed 10 mm. Regarding the ECG shown in Figure-1 — virtually all 12 leads show diffuse low voltage.
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• Electrical Alternans: As discussed in detail in ECG Blog #83 — The phenomenon of electrical alternans encompasses a beat-to-beat variation in any one or more parts of the ECG recording. It may occur with every-other-beat — or with some other recurring ratio (3:1; 4:1; etc.). Amplitude or direction of the P wave, QRS complex, ST segment and/or T wave may all be affected. Alternating interval duration (of PR, QRS or QT intervals) may also be seen. 
• The ECG in Figure-1 is remarkable — in that further reduction of an already-reduced QRS amplitude is seen in all 12 leads with every-other-beat (The QRS becomes tiny in virtually all 12 leads for every even-numbered beat).

PEARL #1: Regarding Today’s CASE:

Although the list of clinical entities associated with diffuse low voltage and electrical alternans is long (See ECG Blog #272 and ECG Blog #83) — the occurrence of both of these ECG findings in an older patient with known cancer, who presents with shortness of breath — should immediately prompt consideration of a large pericardial effusion as the presumed diagnosis until proven otherwise. 

• Overall — the sensitivity and specificity of ECG for the diagnosis of pericardial effusion is poor. Clinically — it is rare that the ECG even enters into diagnostic deliberations — because the picture of a large, pear-shaped heart on chest x-ray usually prompts immediate consideration of a large pericardial effusion — that can then be rapidly confirmed by bedside Echo. Seeing low voltage on ECG is most often an “after-thought” to the diagnosis.
• The above said — the degree of “low voltage” and the prominence of electrical alternans of every-other-beat in Figure-1 is so extreme — that today’s tracing marks one of those truly rare occasions over my many decades of reviewing ECG cases, in which I found myself immediately thinking, “large pericardial effusion” until proven otherwise.
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• A 3rd ECG finding seen in Figure-1 consistent with the diagnosis of a large pericardial effusion — is the rapid heart rate. While not quite satisfying criteria for sinus “tachycardia” (which is a heart rate ≥100/minute) — the overall heart rate of 90-95/minute adds to our suspicion.
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• To Emphasize: Smaller pericardial effusions often do not produce noticeable ECG abnormalities — which highlights the point that the diagnosis will most often not be made from the ECG. That said, what counts clinically — is appreciation whether an enlarging pericardial effusion is evolving toward pericardial tamponade (which would be a medical emergency). 
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• PEARL #2: While in most cases, the ECG will not predict impending tamponade — an exception may be seen IF there is development of total electrical alternans (ie, of P wave, QRS complex and T wave) — as this finding suggests there may now be tamponade.
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• PEARL #3: Awareness of the above cited ECG findings may be clinically relevant in the patient with a large pericardial effusion that you are following. While definitive diagnosis of a pericardial effusion will have to be made by Echo — Be alert to the following: i) Progressive reduction in QRS amplitude; ii) Increasing heart rate; and, iii) Evolution of electrical alternans into a pattern involving not only the QRS, but also the P wave and T wave. IF you see this combination of ECG findings — Be ALERT to worsening effusion with potential impending tamponade.

Follow-Up in Today’s CASE:

In today's case — malignant metastasis was suspected in the patient whose ECG is shown in Figure-1. Her large pericardial effusion required drainage — with removal of nearly 1 liter of fluid.

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Acknowledgment: My appreciation to Arron Pearce (from Manchester, UK) for the case and this tracing. 

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Related ECG Blog Posts to Today’s Case:

• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
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• ECG Blog #83 — Reviews the phenomenon of Electrical Alternans.
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• ECG Blog #272 — Review the Causes of Low Voltage on ECG.