Friday, December 24, 2010

ECG Interpretation Review #10 (Peaked T Waves, Ischemia vs Hyperkalemia vs Normal Variant)

QUESTION: Interpret the 12-lead ECG below, obtained from an older patient with multiple medical problems (and on multiple medications).
  • Clinically – What do you suspect is going on?
  • Is there ECG evidence of ischemia? (What will have to happen before you'll be able to answer this question? )

Figure 1: ECG obtained from an older patient with multiple medical problems.












      
INTERPRETATION:  The rhythm is sinus at a rate just under 100/minute. The PR and QRS intervals are normal.  The QT looks to be about half the R-R interval, so that it is borderline prolonged. The axis is abnormal. The small amplitude but predominantly negative QRS complex in lead I indicates RAD (Right Axis Deviation) of at least +100 degrees.  There is no chamber enlargement.
  • Q-R-S-T Changes – There appear to be Q waves in leads I,aVL – and QS complexes in V1,V2.  Transition may be slightly delayed, with the QRS becoming more positive only in lead V5. However, the most remarkable finding are the very tall, peaked T waves with narrow base ("Eiffel Tower" effect) in several precordial leads (Figure 2).  This strongly suggests Hyperkalemia.  In addition – T waves are inverted sharply in leads III and aVF of Figure 1, and there is some straight ST segment depression in inferior and anterolateral leads.

Figure 2: Blow-up of Figure 1 — showing tall, peaked T waves ("Eiffel Tower effect" ) of hyperkalemia.


Clinical PEARL: The ECG is the net result of the heart's electrical activity. It is difficult to know the clinical significance of RAD and the ST depression/T wave inversion seen here given the setting of superimposed hyperkalemia.  One will not know the "true" ECG story until the electrolyte disorder (and the ECG changes of hyperkalemia) have been corrected . . .
  • Axis deviation – QRS widening with changes in QRS morphology – and peaked T wave inversion are all examples of ECG abnormalities that may simply be due to the hyperkalemia.

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ECG Changes of Hyperkalemia: In general – the ECG correlates well with the degree of serum potassium elevation  (Figure 3).

Figure 3:  ECG Manifestations of Hyperkalemia.

  • Panel A  – shows a normal ST-T wave.
  • Panel B  – T wave peaking is the earliest change of hyperkalemia.
  • Panel C – The T wave becomes taller and more peaked (K+ ~ 7-8 mEq/L); it almost looks like the Eiffel Tower (tall, peaked, with narrow base) – in contrast to the T wave that is sometimes seen in healthy individuals (lower right box in Figure 3), in which the T wave is rounded, its sides are not symmetric, and it has a broad base.
  • Panel D – P wave amplitude decreases, the PR interval lengthens, and the QRS widens (K+ >8 mEq/L).
  • Panel E – P waves disappear (sinoventricular rhythm) and the QRS becomes sinusoid (K+ >10 mEq/L).  V Fib usually follows.
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    Final Point: All that produces tall, peaked T waves is not necessarily hyperkalemia! Instead, the finding of Twave peaking should prompt one to consider a differential diagnosis of 3 possible causes – with the clinical situation (as well as specific ECG features) providing KEY clues as to which of the 3 is likely to be present.
    1. Hyperkalemia — Suspect as the cause of T wave peaking when the clinical setting is one likely to produce hyperkalemia (ie, renal failure, volume depletion, acidosis, potassium-retaining drugs) – and – when T waves are tall, pointed with steep ascent and near equally steep descent with a narrow base (as seen in Figure 2 ).
    2. Normal (Repolarization) Variant — Suspect when T wave peaking has a more rounded summit with assymetric ascent and descent and a broader base – especially IF the patient is otherwise healthy and without any apparent reason to have hyperkalemia (We saw this in Figure 1 of ECG Review #6).
    3. Ischemia — Although a much less common cause of T wave peaking than hyperkalemia and normal repolarization variants – it should be appreciated that myocardial ischemia (in the area of the left ventricular posterior wall) may sometimes present with the ECG finding of tall, peaked T waves in the anterior leads. Be aware of ischemia as a possible cause of T wave peaking in leads V1,V2,V3 when a patient with known (or suspected) coronary artery disease presents with chest pain – especially if there is other evidence on the tracing to suggest ischemia or infarction (ie, inferior T wave inversion or ST depression).

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    Posted by ECG Interpretation at 12:18 PM