Why is this a high-grade AV block? If at least 3 P-waves are not conduced and there is normal AV conduction before and after, this can be considered a high-grade AV block. In this Holter strip, P1, P2 and all P-waves from P6 onwards are conducted, albeit with a prolonged PR interval (first-degree AV block). P3, P4, P5 are not conducted. A junctional escape beat is seen before P5. P5 can also not be conducted because the specific conduction system is still refractory at this time due to the junctional escape beat.

Furthermore, a long QT time is observed!