Patient: 62-year-old man with severe dilated cardiomyopathy; syncopal episode;
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Analysis of the QRS pattern and diagnosis of ventricular tachycardia
ECG: wide QRS tachycardia; highly fragmented QRS, extreme-right axis; the negative concordance in the precordium (QRS all negative from V1 to V6) is strongly suggestive of the diagnosis of ventricular tachycardia (low probability of having a left bundle branch block-type aberration with a negative QRS in V6; low probability of having a right bundle branch block with negative QRS in V1);
ECG 2: 81-year-old patient with severe ischemic cardiomyopathy; the electrocardiogram shows a wide QRS tachycardia; left delay, right axis; certain elements of this tracing are suggestive of a ventricular tachycardia: right axis, interval of 100 ms between the beginning of the QRS and nadir of the S wave in V2;
ECG 3: 64-year-old man with ischemic cardiomyopathy; wide QRS tachycardia with right delay, left axis; in the setting of a tachycardia with left delay, certain elements are suggestive of a ventricular tachycardia: monophasic pattern (exclusive R) in V1, S wave taller than R wave in V6, left axis deviation; analysis of atrial activation shows a 1:1 retrograde conduction;
ECG 4: 71-year-old patient with an extensive anterior infarction ten years prior with major alteration of left ventricular ejection fraction and apical aneurysm; syncope; the electrocardiogram shows a wide QRS tachycardia; left delay, left axis; certain elements of this tracing are suggestive of a ventricular tachycardia: q wave and qR pattern in V6; greater negative deflection in V2 and V3 than in V1; slow notched intrinsicoid deflection in V1; notch present in the descending branch of the S wave in V1; interval between the beginning of the QRS and nadir of the S wave > 80 ms in V1; a 2:1 retrograde conduction confirms the diagnosis of ventricular tachycardia (P’ wave present in 1 QRS out of 2);
ECG 5: The sinus rhythm electrocardiogram recorded in this patient shows extensive anterior necrosis with persistent elevation (inferior territory and anterior territory) attesting to the left ventricular aneurysm;
Comments: In the presence of a wide QRS tachycardia, various electrocardiographic criteria can be used to differentiate a ventricular tachycardia and a supraventricular tachycardia with conduction aberration.
- The presence of an identical QRS pattern between the sinus rhythm complexes and the tachycardia complexes allow confirming the diagnosis of supraventricular tachycardia although an electrocardiogram in sinus rhythm is not always available at the time of analysis of tachycardia. A change in pattern and width of the QRS is suggestive of a ventricular tachycardia although the discriminative value is limited (possible conduction aberration).
- The detection of capture or fusion complexes during tachycardia confirms the diagnosis of ventricular tachycardia.
- The presence of atrioventricular dissociation is quasi-pathognomonic of ventricular tachycardia even if it is necessary to eliminate certain relatively rare diagnoses (Hisian or nodal tachycardia with ventricular aberration and retrograde block, tachycardia due to Mahaim fibers in the anterograde direction and nodal block). Moreover, the pinpointing of P waves is sometimes difficult.
The rate and regularity of the tachycardia are not distinctive features; the discriminative value of the duration of the QRS complexes is also low. Ventricular tachycardias have on average wider ventriculograms than supraventricular tachycardias, although certain exceptions limit the discriminative value of this parameter: the QRS complexes can be relatively narrow (sometimes < 120 ms) in septal or fascicular ventricular tachycardias; conversely, certain patients with severe cardiomyopathy have extremely wide sinus QRS complexes invalidating this criterion for differentiating the origin of the tachycardia. It nevertheless appears that in a patient with a prior narrow QRS and without antiarrhythmic treatment or ventricular preexcitation, a tachycardia QRS > 140 ms is suggestive of a ventricular origin.
Analysis of the ventriculogram patterns can also allow discriminating the origin of the tachycardia. Different algorithms have been proposed but are only of relevance if the patient has no major abnormalities of the baseline ECG (extensive sequela of necrosis with very broad QRS) or anterograde atrioventricular pre-excitation and is not under a class I antiarrhythmic treatment (which induce a widening of the rate-dependent QRS complexes). Many of these criteria overlap. The morphological analysis of QRS complexes has certain limitations, one example being branch-to-branch tachycardias where the pattern will, by definition, be that of a typical bundle branch block despite its ventricular origin.
Various parameters can be analyzed in order to differentiate the origin of a wide QRS tachycardia:
- QRS axis: extreme axis deviations between 90 and 180 degrees are rarely observed but are specific to a ventricular origin; in the case of a tachycardia with right delay, a left axis deviation also suggests a ventricular origin;
- absence of RS complex in precordial leads, presence of positive concordance (QRS complexes all positive) or negative concordance (QRS complexes all negative) throughout the precordium (V1-V6) are all suggestive of a ventricular tachycardia;
- the diagnosis of ventricular tachycardia is probable if the interval between the beginning of the R wave and the nadir of the S wave in a precordial lead is greater than 100 ms;
- in the presence of a tachycardia with right delay, various criteria are indicative of a ventricular origin: monophasic (exclusive R) or biphasic (QR) pattern in V1, S wave taller than the R wave in V6, left axis deviation; on the other hand, a triphasic pattern with a large positive late deflection in V1 and a S wave smaller than the R wave in V6 tends toward a conduction aberration and a supraventricular tachycardia;
- in the presence of a tachycardia with left delay, various criteria point to a ventricular origin, none of which taken individually have a very high value: a QRS axis deviated to the right, deeper negative deflections in V2 or V3 than in V1, a large R wave (> 30 ms) in V1 or V2, a slow and sometimes notched intrinsicoid deflection in V1, a notch in the descending branch of the S wave in V1 or V2; the V6 lead is not very contributory unless there is a Q wave with QR pattern.
The Brugada criteria have been proposed, with satisfactory results, for discriminating the origin of a large QRS tachycardia based on the surface electrocardiogram.
This algorithm is decomposed into 4 steps but can only be used in the absence of antiarrhythmic treatment:
- step 1: the absence of RS complexes in precordial leads is pathognomonic of a ventricular tachycardia,
- step 2: the presence of RS complexes whose peak occurs 100 ms after the QRS onset is also suggestive of ventricular tachycardia,
- step 3: search for an atrioventricular dissociation,
- step 4: when the tachycardia is not classified after the first 3 steps, the analysis of the morphological criteria in V1 and V6 as explained above are applied.
Take-home message: in the presence of a wide QRS tachycardia, various electrocardiographic criteria can be used to differentiate ventricular tachycardia from supraventricular tachycardia with conduction aberration: an identical QRS pattern in sinus rhythm and in tachycardia is suggestive of a supraventricular origin; the detection of capture or fusion complexes confirms the diagnosis of ventricular tachycardia; the presence of atrioventricular dissociation is quasi-pathognomonic of ventricular tachycardia. In absence of these criteria, analysis of the QRS pattern may allow discriminating the origin of the arrhythmia (typical bundle branch block pattern indicative of a supraventricular origin, distant pattern of a bundle branch block indicative of a ventricular origin).
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