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Vol. 73. Issue 12.
Pages 1064 (December 2020)
ECG Contest
DOI: 10.1016/j.rec.2020.04.015
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Response to ECG, November 2020
Respuesta al ECG de noviembre de 2020
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Giampaolo Vettaa, Bruna Creab, Pasquale Creaa,
Corresponding author
pasqualecrea@hotmail.it

Corresponding author:
a Cardiology Unit, Department of Clinical and Experimental Medicine, University of Messina, Messina, Italy
b Internal Medicine, San Luigi Gonzaga Hospital, Orbassano, University of Turin, Turin, Italy
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Rev Esp Cardiol. 2020;73:95110.1016/j.rec.2020.04.014
Giampaolo Vetta, Bruna Crea, Pasquale Crea
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The correct response is 2. Bradycardia-dependent or phase 4 block is a typical phenomenon of a pathological intraventricular conduction system, depending on spontaneous diastolic depolarization. During a long diastole, the tissue fibers undergo progressive hypopolarization. As a result, the tissue will not be able to depolarize. The ability to depolarize can only be recovered with an escape or premature beat, as it restores the membrane's potential to its physiological resting potential. In the ECG (figure 1) the pause after a nonconducted premature atrial beat started phase 4 III degree atrioventricular block. An escape junctional beat permitted recovery of atrioventricular conduction.1

Figure 1
(0.21MB).

Response 4 is obviously wrong because phase 3 block is a tachycardia-dependent block that occurs when an early impulse arrives at the conduction tissue during the refractory period and is not conducted.

Atrioventricular block due to vagal hypertonia is usually nocturnal and anticipated by progressive sinus rhythm slowing and PR interval prolongation (response 1, incorrect).

The absence of manifested junctional extrasystoles or other indirect signs of concealed junctional extrasystole, such as abrupt PR interval prolongation, makes this hypothesis unlikely (response 3, incorrect).2

References
[1]
M.B. Rosenbaum, M.V. Elizari, R.J. Levi, G.J. Nau.
Paroxysmal atrioventricular block related to hypopolarization and spontaneous diastolic depolarization.
Chest., 63 (1973), pp. 678-688
[2]
L. Schamroth, B. Surawicz.
Concealed interpolated A-V junctional extrasystoles and A-V junctional parasystole.
Am J Cardiol., 27 (1971), pp. 703-707
Copyright © 2020. Sociedad Española de Cardiología
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