[Wide QRS complex tachycardia: an old and new problem].
The correct diagnosis of wide QRS complex tachycardia is an old problem, but it is still a new problem since no simple approach aimed at solving it is up to now available, despite the amount of research devoted to this topic. A wide QRS tachycardia can be: 1) ventricular tachycardia; 2) supraventricular tachycardia with bundle branch block that may be either preexisting or due to aberrant conduction, namely tachycardia-dependent; a further possibility is the effect of antiarrhythmic drugs, which slow down intraventricular conduction, resulting in marked QRS complex widening; 3) supraventricular tachycardia with conduction of impulses to the ventricles over an accessory pathway (preexcited tachycardia). The origin of a wide QRS complex tachycardia can be reliably identified using a "holistic" approach, namely taking into account all of the available items: no single criterion, thus, is able to provide a simple and quick solution to the problem in all cases. The electrocardiographic signs are, without any exception, suggestive of ectopy, namely ventricular origin of the impulses; supraventricular tachycardia with aberrant conduction may be diagnosed only by excluding all of the items favoring ectopy. The classic diagnostic criteria include: 1) atrio-ventricular dissociation, characterized by absence of any relationship between QRS complexes and P waves; this phenomenon is at times immediately recognizable but more often can be discovered only by means of a detailed analysis of the tracing; 2) second degree ventriculo-atrial block, characterized by a relationship between QRS complexes and P waves, but with more ventricular complexes than P waves; 3) fusion and/or capture beats; 4) concordant precordial pattern, a sign that can be also expressed as absence of RS (or even rs, Rs, rS) complexes in the precordial leads; 5) an interval > 100 ms from the beginning of the QRS complex to the nadir of S wave in any precordial lead. Vagal maneuvers and analysis of previous ECGs recorded during sinus rhythm, if available, can provide further keys to the diagnosis. Some criteria proposed in the past, such as QRS axis or ventricular complex duration, are nowadays no longer considered; in addition, it has been demonstrated that items such as age, hemodynamic status, heart rate and regularity of R-R intervals may be misleading and should not be taken into account. Analysis of QRS configuration in leads V1 and V6 is a keystone in distinguishing the origin of wide QRS tachycardia: diagnostic criteria rely upon the assumption that aberration is due to a functional bundle branch block, whereas ectopy derives from a totally abnormal activation of the ventricles. Aberration, thus, results in a "typical" bundle branch block morphology, whereas ectopy is expressed by an "atypical" bundle branch block. Specific criteria, based on analysis of leads V1 and V6, have been developed to distinguish the two conditions from each other. The criteria based on QRS configuration, however, suffer from limitations since unexpected complicating factors, such as a previous myocardial infarction, can result in an "atypical" form of bundle branch block even in the presence of supraventricular tachycardia. A new algorithm has recently been introduced, based on analysis of lead aVR only. Any of the following features, observed in this lead, pinpoints a diagnosis of ventricular tachycardia: 1) a dominant R wave (R or Rs complexes); 2) an initial q or r wave with duration > 40 ms (qR or rS complexes); 3) a notch in the descending Q wave limb in a negative (Qr or QS) complex. In the absence of these signs, the ratio between the voltages recorded during the first and the last 40 ms of the QRS complex helps distinction between ectopy and aberration: a ratio < or = 1 suggests ventricular tachycardia whereas a ratio > 1 indicates supraventricular tachycardia. A hard diagnostic problem is associated with preexcited tachycardia, the condition resulting whenever supraventricular tachycardia impulses are conducted to the ventricles over an accessory pathway. This situation is far more rare than ectopy and aberration, and can be ruled out in the presence of negative precordial concordance (QS complexes in all the chest leads) or deep q waves in a precordial lead other than V1. A QRS morphology not consistent with any of the typical patterns observed in the various locations of the accessory pathways rules out a preexcited tachycardia, too.
Oreto
Giuseppe
G
Dipartimento di Medicina e Farmacologia, Università degli Studi, Messina. oretogmp@tin.it
Luzza
Francesco
F
Satullo
Gaetano
G
Donato
Antonino
A
Carbone
Vincenzo
V
Calabrò
Maria Pia
MP
D003663:Decision Trees; D004562:Electrocardiography; D006801:Humans; D013610:Tachycardia / Q000175:diagnosis* / Q000503:physiopathology