Stem: 77 year old woman had back pain yesterday, and several episodes of feeling faint today. She has not experienced any anterior chest discomfort. On arrival her blood pressure was 110/80 mm Hg, her JVP was 0.5 cm, and there was no leg oedema. Examination of the lungs and heart and abdomen was normal.
+ List the significant findings in the ECG and provide the most likely or important diagnosis
- The rhythm is regular, and the ventricular rate is about 26 beats per minute
- The QRS complexes have a right bundle branch block morphology and left axis deviation is present i.e a bifasicular block is present (1)
- Each QRS complex is preceded by three P waves, only one of which is conducted. The PR interval of the conducted P waves is constant (at 0.20 seconds). The atrial rate is about 80 beats per minute. The underlying rhythm is sinus rhythm with 3:1 AV block; this is termed advanced 3:1 AV block rather than Type II second degree heart block
- The QT interval is prolonged at 600 msec (2)
- Horizontal ST depression is present in Leads I, II, V4 to V6; sagging ST depression is seen in Lead V3 (3)
- Relevant normal observations: The transition zone is between V2 and V3
- The PR interval of the conducted P waves is at the upper limit of normal; if it was longer than the 0.20 seconds seen in this case the term trifasicular block would be used.
- Measurement of the QT interval is complicated because P waves merge into the end of each T wave. The QT interval is prolonged in both congenital heart block and acquired heart block; this prolongation can lead to the development of torsade de pointes. The QTc in this case (using the Framingham formula for QTc [QTc = QT + 0.154(1-RR) where RR = 60/HR]) is still prolonged at 598 msec.
- These changes raise the possibility of ischaemia
- The patient received an intravenous infusion of isoprenaline to increase the ventricular rate to 50 beats per minute, and had a permanent pacemaker inserted the next day.