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Sinus Bradycardia



This strip shows a rate slower than 60 beats per minute (it is 45) , with a P-wave preceding each QRS and a QRS following each P-wave.  Thus the rhythm is sinus bradycardia.   Other notable features of this strip are these:  the P-R interval is normal (0.18 seconds).  The QRS shape is abnormal, and the QRS duration is prolonged (0.12 seconds), both indicating an intraventricular conduction delay.  The T-waves are inverted, and the Q-T interval is 0.56 second, well above the upper limit of normal for this heart rate.   These suggest either myocardial ischemia, a resolving myocardial infarction, cardiomyopathy, or a medication effect.  So, in this strip we see abnormality of rate (the bradycardia), abnormality of depolarization, implicating the specialized conduction system (the prolonged QRS duration and the QRS shape), and abnormality of repolarization (the prolonged QT interval).