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Sinus Pauses example two



Look at the brief pauses, and the T-waves in leads II and III.  Following the T-waves, there is an extra deflection called a U-wave.  This can be caused by hypokalemia, or by antiarrhythmic drugs such as quinidine.  This is an abnormality of delayed repolarization: note that the Q-T interval is 0.48 seconds, and the Q-U interval is close to 0.60 seconds.  The U-waves seen here are of moderate size.   Their presence, taken together with the prolonged QT, a slightly prolonged QRS of 0.10 seconds, and the irregular rate, suggest that these are quinidine effects.