Entrainment of ventricular tachycardia in postoperative tetralogy of Fallot

Electrocardiographic recognition of benign and malignant right ventricular arrhythmias

Ventricular arrhythmias (VAs) can originate from different anatomical locations of the right ventricle. Ventricular arrhythmias originating from right ventricle have unique electrocardiographic (ECG) characteristics that can be utilized to localize the origin of the arrhythmia. This is crucial in pre-procedural planning particularly for ablation treatments. Moreover, non-ischaemic structural heart diseases, such as infiltrative and congenital heart diseases, are associated with the VAs that exhibit particular ECG findings. This article comprehensively reviews discriminatory ECG characteristics of VAs in the right ventricle with and without structural right ventricular diseases.

Transient entrainment: the evolution of a medical concept from description to prescription

Entrainment is a phenomenon that has come to have considerable utility in cardiac electro-physiology diagnosis and treatment; specifically, to identify a zone of slow conduction in a reentrant circuit, a zone hypothetically vulnerable to intervention from the application of RF energy. The observation of entrainment has gone through an evolutionary sequence in the literature, from the initial simple observations of the phenomenon to the present stage of relatively fixed criteria of identification. This article follows the evolution of the specific features of the criteria of entrainment to their current crystallization into features that are suggested to prescribe sites for attempted ablation. This examination of the evolutionary course of the development of the conception of entrainment is of interest not only to cardiac electrophysiology, but also to philosophers of science, by illustrating how scientists emphasize and develop certain observations with the ultimate aim of applying the observations for successful intervention in pathological entities.

Mechanoelectrical interaction in tetralogy of Fallot. QRS prolongation relates to right ventricular size and predicts malignant ventricular arrhythmias and sudden death

BACKGROUND

Life-threatening ventricular arrhythmia and sudden death remain serious late complications after tetralogy of Fallot repair. Nevertheless, there remains no clear way of predicting which patients are at risk.

METHODS AND RESULTS

The study population included a total of 178 adult survivors (mean follow-up, 21.4 years) of tetralogy of Fallot repair who were currently attending our clinic. Mechano-electrical relations were sought in 41 of the patients (mean follow-up, 23.6 years) who were operated on by one surgeon and who were prospectively studied with a 12-lead ECG, chest radiography, and two-dimensional and Doppler echocardiography. Nine patients (mean follow-up, 17 years) from the total group of 178 were identified as having had sustained ventricular tachycardia (8 with near-miss sudden death), and their ECGs, Holter monitor readings, electrophysiological studies, and chest radiographs were reviewed. The case notes of an additional 4 patients with postoperative sudden cardiac death also were available for review. QRS duration in the 41 patients in whom mechanoelectrical interaction was sought ranged between 90 and 200 milliseconds and correlated with cardiothoracic ratio (CTR) on chest radiography (r = .64, P < .001) and with right ventricular size on echocardiography (r = .43, P < .02). Twenty of the 41 patients had restrictive right ventricular Doppler physiology (reduced ventricular compliance) with mean QRS duration of 129.3 +/- 20 milliseconds and mean CTR of 0.51 +/- 0.03. The remaining 21 patients with no evidence of right ventricular restriction had prolonged QRS duration of 157.5 +/- 13.2 milliseconds (P < .001) and CTR of 0.55 +/- 0.04 (P < .04) compared with the restrictive. In the 9 patients with ventricular tachycardia, the QRS duration ranged from 180 to 230 milliseconds (mean, 198.9 +/- 17.6 milliseconds), and the CTR ranged from 0.54 to 0.9 (mean, 0.67 +/- 0.12) (P < .0001 and P < .01, respectively, compared with patients without life-threatening arrhythmias). All patients with documented sustained ventricular tachycardia and the 4 patients with sudden death had a QRS duration of > or = 180 milliseconds (100% sensitivity).

CONCLUSIONS

Chronic right ventricular volume overload after tetralogy of Fallot repair is related to diastolic function and correlated with QRS prolongation. The risk of symptomatic arrhythmia is high when marked right ventricular enlargement and QRS prolongation develop. A QRS duration on the resting ECG of > or = 180 milliseconds is the most sensitive predictor of life-threatening ventricular arrhythmias yet described.

Surgical treatment of ventricular tachycardia after surgical repair of tetralogy of Fallot. Relation between intraoperative mapping and histological findings

BACKGROUND

The mechanism of ventricular tachycardia (VT) after correction of tetralogy of Fallot (TF) is poorly understood. The purpose of this study was to examine the histopathology of the arrhythmogenic area detected by intraoperative mapping.

METHODS AND RESULTS

The patients were three men who underwent radical surgery for TF at age 3, 3, or 5 years, respectively. VT developed at 8, 9, or 11 years, respectively, after surgery, and shock developed during VT in every case. The ECG revealed monomorphic VT in two cases and polymorphic VT in one case. Induction of VT resulted in a wide left-axis deviation-pattern QRS with cycle lengths varying between 260 and 330 milliseconds. The VT origin was identified at the right ventricular outflow tract (RVOT). A radical operation was performed with the patient under cardiopulmonary bypass. On epicardial mapping, delayed activation of the RVOT was recorded during sinus rhythm, and clockwise circus movement of the macroreentry current during VT on the right ventricular free wall was documented in each case. The VTs were treated successfully by surgical resection and cryoablation of the myocardium. In every patient, histology of the myocardial specimens showed degeneration, adiposis, fibrosis, inflammatory cell infiltration, and scattered myocyte islets. These lesions corresponded anatomically to the area of myocardium in which delayed activation was evident during epicardial mapping.

CONCLUSIONS

The results of this study indicate that patients with VT after radical correction of the TF have abnormal histopathological findings at the site of the prior right ventriculotomy scar. These lesions were noted within the region of delayed activation found during epicardial mapping and were found to be a part of the reentrant circuit.

Radiofrequency catheter ablation of right ventricular outflow tract tachycardia late after complete repair of tetralogy of Fallot using the pace mapping technique

While surgical repair of tetralogy of Fallot has improved the long-term outlook for this patient population, sudden death late after repair remains a problem. Ventricular tachycardia (VT) originating in the right ventricular outflow tract (RVOT) is a well described, clinically important finding following surgical repair of tetralogy and a number of investigators suggest that this VT plays a critical role in the etiology of sudden death. We report two patients with RVOT VT late after repair of tetralogy who underwent successful radiofrequency ablation of their tachycardia.

Ventricular tachycardia after surgical repair of tetralogy of Fallot: results of intraoperative mapping studies

OBJECTIVES

Four patients with previous repair of tetralogy of Fallot and ventricular tachycardia underwent map-guided surgery to ablate the arrhythmias.

BACKGROUND

Although patients with repaired tetralogy of Fallot are at increased risk of sudden death due to ventricular tachycardia, little is known of the origin and mechanism of this arrhythmia.

METHODS

A customized right ventricular balloon with 112 electrodes was used to record endocardial activation and, where possible, simultaneous epicardial recordings were obtained with a sock electrode array. Three patients had an aneurysm of the right ventricular outflow tract and one had a septal aneurysm. All had moderate to severe pulmonary valve insufficiency. Preoperative electrophysiologic study demonstrated inducible rapid (cycle length 180 to 300 ms) hemodynamically unstable monoform ventricular tachycardias.

RESULTS

Intraoperatively, five different tachycardias (two in one patient) were induced and mapped. The sites of earliest activation were located in the subendocardium of the right ventricular outflow tract in all, but they varied widely among the septum, free wall and parietal band and could not be identified by visible scar. All were due to a macroreentrant circuit initiated by a critical delay in activation beyond a functional arc of block. Two patients treated by cryoablation while the heart was beating and perfused at normal temperature had inducible ventricular tachycardia postoperatively. In the two subsequent patients, the application of cryoablation under anoxic cardiac arrest resulted in noninducibility of arrhythmia.

CONCLUSIONS

Ventricular tachycardia in tetralogy of Fallot in these four patients was caused by macroreentry in the right ventricular outflow tract. Surgical success depends on detailed mapping and cryoablation under anoxic cardiac arrest. In patients at risk of sudden death, map-directed surgery may offer distinct advantages over either implantable devices or drug therapy.

Electrocardiographic signal-averaging during atrial pacing and effect of cycle length on the terminal QRS in patients with and without inducible ventricular tachycardia

Electrocardiographic signal-averaging during sinus rhythm (61 to 99 beats/min) and atrial pacing (100 to 171 beats/min) were performed to determine the effect of heart rate on late potentials in 15 patients without (group 1) and 7 patients with (group 2) inducible sustained ventricular tachycardia (VT). In sinus rhythm (79 +/- 12 vs 77 +/- 12 beats/min, difference not significant), the duration of the low-amplitude signal less than 40 microV was longer in group 2 than group 1 (43 +/- 21 vs 26 +/- 8 ms, p = 0.034) and more patients had late potentials (57 vs 7%, p = 0.021), but QRS duration (121 +/- 32 vs 98 +/- 19 ms) and terminal voltage (33 +/- 33 vs 50 +/- 26 ms) were not significantly different. With atrial pacing in group 1 (128 +/- 16 beats/min), 3 patients developed a simultaneous decrease in terminal voltage and an increase in terminal QRS duration consistent with a late potential, but mean total and terminal durations were unchanged. Terminal voltage increased (50 +/- 26 to 59 +/- 40) but not significantly. With atrial pacing in group 2 (119 +/- 12 beats/min) all patients either had a late potential or developed a simultaneous decrease in terminal voltage and an increase in terminal QRS duration (p = 0.001 vs group 1). Root mean square (p = 0.001 vs group 1). Root mean square voltage decreased (33 +/- 23 to 22 +/- 23) and became significantly different from group 1 (p = 0.017). Mean QRS duration, root mean square terminal voltage and low-amplitude terminal QRS duration, however, were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Entrainment onset in atrioventricular reciprocating tachycardia: value in bypass tract localization and relationship to the preexcitation index

The timing of entrainment onset has been shown to correlate with the conduction time to critical elements of a tachycardia circuit in a pacemaker model of reentrant ventricular tachycardia (VT). The utility of this method in evaluating clinical reentrant tachycardias was therefore evaluated in 24 patients with symptomatic Wolff-Parkinson-White syndrome and single bypass tracts (left free wall in 17, posteroseptal in 5, anteroseptal in 1, and right free wall in 1). Right ventricular apex (RVA) pacing during orthodromic atrioventricular reentrant tachycardia (oAVRT) at 10-70 msec less than tachycardia cycle length demonstrated concealed entrainment of the tachycardia in all patients studied. An entrainment index (EI), defined as the minimal prematurity of the ventricular stimulus that first resulted in atrial reset, was calculated from multiple entrainments in each patient. The EI was 121 +/- 25, 83 +/- 19, and 55 msec for left free wall, septal, and right free-wall bypass tracts, respectively (P = 0.004 for difference between left free wall and septal). A corrected EI, derived by subtracting the amount of atrial reset from the EI, gave values of 108 +/- 22 and 71 +/- 17 msec for left free wall and septal bypass tracts (P = 0.001). These values were compared to the preexcitation index (PI) by linear regression analysis in these patients. The PI correlated closely with both the EI and the corrected EI (r = 0.90 and 0.93, respectively), but the PI could only be derived in 12/17 (71%) left free-wall tachycardias versus the EI in 17/17 (100%) (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Entrainment onset in a pacemaker model of reentrant ventricular tachycardia: insight into localization of critical elements of a reentrant circuit

We investigated entrainment in a pacemaker model of reentrant ventricular tachycardia (VT) created in the intact dog heart using a VAT pacemaker with both electrodes on the ventricular epicardium. This produced an incessant wide QRS tachycardia originating from the pacing site with a cycle length equal to the conduction time between the sensing and pacing site plus the pacemaker AV delay. The conduction time between entrainment sites and the critical elements of the reentrant pathway (sensing and pacing sites) was determined by pacing at a comparable cycle length during sinus rhythm. Entrainment was achieved in 12 tachycardias with pacing at 1-4 sites at cycle lengths 10-100 msec shorter than tachycardia and confirmed by constant QRS fusion, progressive QRS fusion, and coupling of the first nonpaced QRS or intracardiac electrogram at the entraining cycle length. By least squares regression, the timing of entrainment onset (first reset of pacing or sensing site electrogram) measured by the prematurity of the local electrogram at the entraining site was highly correlated to the shortest conduction time between the entraining site and the circuit (F value of 84.7 and R = 0.752 [P less than 0.001]). Therefore, the timing of entrainment onset maybe useful in predicting the conduction time from the entraining site to critical elements of a reentrant circuit and may assist in localization of the reentrant pathway.

Entrainment of ventricular tachycardia by sinus rhythm

Entrainment of ventricular tachycardia (VT) may be manifest as fixed and progressive QRS fusion with ventricular and, rarely, atrial pacing. Only a single example of spontaneous VT entrainment by another rhythm, rapid atrioventricular nodal tachycardia, has been reported. This article describes an example of fixed and progressive QRS fusion between conducted sinus rhythm and VT consistent with entrainment. In contrast to entrainment with pacing, entrainment of VT by sinus rhythm occurred with drug-mediated arrhythmia slowing and demonstrated progressive QRS fusion at a constant cycle length. However, it did not demonstrate unfused but entrained QRS complexes. The resulting short PR interval and wide QRS mimicked a preexcited rhythm.