Page 61 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answers 3, 4 ECG Cases

Answer 3
VetBooks.ir 1 ECG 3 shows sinus tachycardia.

2 • The average heart rate is 200 bpm and the rhythm is regular. There is a normal P, QRS, and
T wave for each beat.
• Sinus tachycardia is mediated by increased sympathetic tone and can be a normal response to stress
or exercise, or secondary to systemic conditions such as sepsis, fever, hypovolemia, shock, or heart
failure.
• Sinus tachycardia can be differentiated from SVT through its gradual acceleration and deceleration in
response to stress and the absence of other clinical signs in instances of excitement or exercise.

Answer 4

1 ECG 4 demonstrates a particular type of polymorphic VT called torsade de pointes.
2 • There is a characteristic illusion of a twisting of the QRS complex around the baseline. The ECG has
an undulating appearance with varying QRS amplitudes. Torsade de pointes can degenerate into VF,
which is a terminal arrhythmia if not quickly defibrillated.
• Various causes have been implicated in this dangerous arrhythmia, including adverse effects from
certain sodium- or potassium-channel blocking antiarrhythmic drugs, and/or electrolyte or metabolic
disturbances (hypokalemia, hypocalcemia, hypomagnesemia, acidosis) that prolong the QT interval.
VPCs in the presence of long QT intervals predispose the patient to an R-on-T phenomenon,
where the R wave of a subsequent beat occurs during the relative refractory period at the end of
repolarization (T wave) of the preceding beat, and thus may initiate torsades or fibrillation.
• For this arrhythmia, treatment is directed at withdrawal of the offending agent, infusion of
magnesium sulfate, and/or electrical defibrillation.

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