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Vol. 72. Issue 11.
Pages 967 (November 2019)
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Vol. 72. Issue 11.
Pages 967 (November 2019)
ECG Contest
DOI: 10.1016/j.rec.2018.11.005
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Response to ECG, October 2019
Respuesta al ECG de octubre de 2019
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Pasquale Creaa,
Corresponding author
pasqualecrea@hotmail.it

Corresponding author:
, Angela Nicoterab, Teresa Creac
a Cardiology Unit, Department of Clinical and Experimental Medicine, University of Messina, Italy
b Cardiology Unit, Papardo Hospital, Messina, Italy
c Internal Medicine, Department of Clinical and Experimental Medicine, University of Messina, Italy
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Rev Esp Cardiol. 2019;72:86610.1016/j.rec.2018.11.006
Pasquale Crea, Angela Nicotera, Teresa Crea
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The correct answer is number 3. As shown in Figure 1, the P-P cycle exactly doubles. This finding strongly suggests a 2:1 sinoatrial (S-A) block. Sympathovagal imbalance and respiratory sinus arrhythmia would have generated a gradually lengthening and shortening of the P-P cycle in a cyclical fashion, usually corresponding to the phases of the respiratory cycle or other autonomic reflexes. Thus, answers 1 and 2 are incorrect. A concealed atrioventricular (A-V) node reentry cannot explain sinus node depression. Moreover, the ECG would have shown a trigger, preceding the pause, such as a Wenckeback phenomenon or a premature atrial impulse.1 For this reason, answer 4 is incorrect.

Figure 1
(0.2MB).

The sinus impulse is only recorded by the ECG once it has left the sinus node and activated the atrium, thereby resulting in the P wave.2 Delay in conduction at the S-A junction, such as that occurring during a first-degree S-A block is, therefore, not visible electrocardiographically. Second-degree S-A blocks can be revealed by a careful analysis of the ECG. A Wenckebach conduction defect at the S-A level will present as progressive acceleration of the P-P intervals, analogously to the progressive acceleration of the R-R intervals in an A-V Wenckebach disturbance. Pause is less than twice the preceding P-P cycle.3 In contrast, an abrupt doubling of the P-P cycle excludes a second-degree Mobitz type 2 or a 2:1 S-A block. It is worth noting that sinus bradycardia and 2:1 S-A block are indistinguishable on an ECG, unless an abrupt change in heart rate clarifies the underlying mechanism. Advanced S-A block will be revealed by a pause that is a multiple of> 2 of the P-P cycle. ECG of third-degree S-A block is analogous to sinus arrest.

References
[1]
G. Oreto, A. Consolo, I.M. Scimone.
Manifest and concealed AV nodal reentry in Wenckebach type of AV conduction with AV junctional escape rhythm.
J Electrocardiol., 29 (1996), pp. 333-336
[2]
M.A. de Almeida Henriques, L. Schamroth.
Sinus rhythm complicated by second-degree sino-atrial block.
Heart Lung., 5 (1976), pp. 137-138
[3]
L. Schamroth, E. Dove.
The Wenckebach phenomenon in sino-atrial block.
Br Heart J., 28 (1966), pp. 350-358
Copyright © 2018. Sociedad Española de Cardiología
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