Discussion Electrocardiograma 4
The ECG shows an irregular rhythm. that consists of one to three consecutive sinus beats at 88 per rninute. followed by runsof tachycardia of three to five beats in duration at approximately 150 per rninute.
The ORS complexes are the same in the sinus and tachycardia beats indicating that the tachycardia is supraventricular- The first beat of each run of tachycardia is initiated by a premature P wave (superimposed on the T wave} with a longer PR interval than that of the sinus beats. The second and subsequent beats during the tachycardia are preceded by P waves that have a different morphology than the initiating atrial premature beat- They are inverted in the inferior leads consistent with retrograde atrial activation- The retrograde P waves fall closer to the following ORS complex than to the preceding one. Thus. this is a long RP tachycardia.
This pattern is characteristic of a reentrant tachycardia in which the retrograde conduction is through a slowly conducting pathway- The mechanism is similar to that of atypical AV nodal reentrant tachycardia (AVNRT`)- The retrograde pathway is slow resulting in the long RP interval. Ectopic atrial tachycardia can also cause a long RP tachycardia with inverted P waves in the inferior leads. The mode of onset indicates the reentrant mechanism in the present case.
When a long RP tachycardia continually starts and stops and is present for rmuch of the 24 hours per day, it is usually designated as the perrnanent forrn of junctional reciprocating tachycardia (PJRT)- Typical and atypical AVNRT usually occur in discrete paroxysms lasting longer, but occurring at intervals more widely separated in time, than the nearly continuous runs of tachycardia seen in PJRT. The rate of PJRT is often in the range of 110 to 140 in adults, contrasted with the usually faster rates of 150 to 220 in AVNRT. The present case is intermediate with regard to the rate. PJRT is usually classified with the tachycardias caused by reentry via accessory pathways. However, the accessory pathway in PJRT is physiologically similar to AV nodal tissue. and is also usually located close to the AV node. Such pathways have even been termed “accessory AV nodes”. PJRT is particularly likely to induce the tachycardia-related reversible cardiomyopathy syndrorne, because it is often present nearly continuously for months or years. It can usually be cured by radiofrequency catheter ablation.
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