Abstract
Supraventricular tachyarrhythmias may be caused by macroreentry circuits involving the AV node and accessory pathways. This paper reports a case of suspected orthodromic atrioventricular reciprocating tachycardia in an 18-month-old Dalmatian admitted with dyspnea and a lifelong history of fatigue. Cardiac auscultation documented a regular fast pace with no heart murmurs. The electrocardiogram characteristics were consistent with supraventricular tachycardia, with very regular RR interval and narrow QRS complexes. At lead II, we identified negative P waves buried within the ST segment, which resulted in a RP-to-PR ratio of 0.60, but in aVR these P waves were positive, suggesting a retrograde conduction of electrical impulses throughout the atrial myocardium. The echocardiographic study showed volume overload, and a decreased fractional shortening was calculated when SVT was sustained, highlighting its impact on systolic function. This is likely the first description of an orthodromic atrioventricular reciprocating tachycardia in a Dalmatian, and although cardiac mapping was not available to confirm this suspicion, all electrocardiograpic features were supportive of such arrhythmia.
Highlights
Supraventricular tachycardias (SVT) include all forms of tachycardia that arise above the bifurcation of the bundle of His or have dependent mechanisms of it [1]
This paper reports a case of suspected orthodromic atrioventricular reciprocating tachycardia in an 18month-old Dalmatian admitted with dyspnea and a lifelong history of fatigue
At lead II, we identified negative P waves buried within the ST segment, which resulted in a RP-to-PR ratio of 0.60, but in aVR these P waves were positive, suggesting a retrograde conduction of electrical impulses throughout the atrial myocardium
Summary
Supraventricular tachycardias (SVT) include all forms of tachycardia that arise above the bifurcation of the bundle of His or have dependent mechanisms of it [1]. The OAVRT requires a reentrant circuit containing an atrioventricular accessory pathway [3], which is constituted by muscle fibers capable of generating action potentials and electrical conduction parallel to the atrioventricular node and His-Purkinje system between the atrium and ventricles [4]. These accessory pathways are either single or multiple, usually have bidirectional conduction capability and can be classified according to its location over the atrioventricular sulcus. This is different from the classical Wolff-Parkinson-White syndrome, in which the accessory pathway is solely used to conduct impulses antegradely [3]
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