ECG 62A Analysis: Ventricular tachycardia (sustained monomorphic)
ECG 62A shows a regular rhythm at a rate of 220 bpm. The QRS complex duration is increased (0.18 sec), and the morphology is not typical for either a right or left bundle branch block. Although there are no obvious P waves seen, there are inconsistent abnormalities of the ST-T waves, best seen in leads I (↑) and V1 (↓) .
The variability in the ST-T waves may be due to superimposed P waves or may be differences in repolarization. There is also variability in the QRS complex morphology seen in lead V1 (^). Such variability is not seen in a supraventricular tachycardia in which depolarization and repolarization are uniform, as the activation of the ventricle follows the same pathway each time. Thus, every QRS complex and ST-T wave is the same. In ventricular tachycardia, the activation of the left ventricle is not using the normal His-Purkinje system, but rather an alternative pathway that results in direct ventricular activation. The activation sequence may be variable, accounting for differences in the QRS complex. The abnormalities in ventricular depolarization is associated with abnormalities in ventricular repolarization, accounting for the ST-T wave changes.
ECG 62B Analysis: Normal sinus rhythm, right atrial hypertrophy (abnormality), first-degree AV block (prolonged AV conduction), old lateral and anteroapical myocardial infarction, left ventricular aneurysm, low voltage in limb leads
ECG 62B shows a regular rhythm at a rate of 78 bpm. There is a P wave before each QRS complex (+) and the PR interval is constant (0.26 sec). The P waves are positive in leads I, II, aVF, and V4–V6.
Hence this is a normal sinus rhythm with a first-degree AV block (prolonged AV nodal conduction). The P waves are tall and peaked in leads II and aVF and all positive in lead V1, consistent with right atrial hypertrophy or a right atrial abnormality. The QRS complex duration is normal (0.08 sec) and there is a normal axis between 0° and +90° (positive QRS complex in leads I and aVF).
There is low QRS voltage in the limb leads (< 5 mm in each lead). The QT/QTc durations are normal (380/430 msec). There are Q waves in leads I and aVL (^), consistent with a lateral wall myocardial infarction. There is also a QS complex in leads V1–V2 (↓), suggestive of an anteroseptal myocardial infarction. Seen in leads I and V4–V5 (▼) are ST-segment elevations, suggesting that there is a left ventricular aneurysm as a result of the previous infarction.
Lastly, there are T-wave abnormalities (↑) in leads I, II, aVR, aVF, and V4–V6. Sustained monomorphic ventricular tachycardia in a patient with a previous myocardial infarction and a left ventricular aneurysm is related to scar with resultant reentrant circuit and is not a result of ischemia.