Repetitive Monomorphic Ventricular Tachycardia Research Articles

Adenosine-sensitive ventricular tachycardia: a conceptual approach.

Idiopathic ventricular tachycardia (VT) is a term that refers to tachycardia that arises from ventricles devoid of apparent structural abnormalities. This form of VT is now recognized to be related to several distinct entities and includes a reentrant form typically located in the region of the left posterior fascicle, an automatic form that may originate from either ventricle, and a form that originates from the right ventricular outflow tract. This last type can account for up to 80% of cases of idiopathic VT and with few exceptions can be further subdivided into repetitive monomorphic VT and paroxysmal stress-induced VT. Evidence has accumulated suggesting that both forms of VT are related to cAMP-mediated triggered activity. The experimental underpinnings of this conclusion as well as the clinical characteristics of this form of idiopathic VT are elucidated in this review.

Mechanism of Repetitive Monomorphic Ventricular Tachycardia

The most common form of idiopathic ventricular tachycardia (VT) is repetitive monomorphic VT (RMVT), which is characterized by frequent ventricular ectopy and salvos of nonsustained VT with intervening sinus rhythm. Unlike most other forms of idiopathic VT, this tachycardia typically occurs at rest and is nonsustained. The mechanism of RMVT is undefined. Because of a common site of origin, the right ventricular outflow tract (RVOT), we hypothesized that RMVT is mechanistically related to paroxysmal sustained, exercise-induced VT, which has been shown to be consistent with cAMP-mediated triggered activity. Therefore, in this study, we sought to identify (1) the mechanism of RMVT at the cellular level by using electropharmacological probes known to activate either stimulatory or inhibitory G proteins and thereby modify intracellular cAMP levels, (2) potential autonomic triggers of RMVT through analysis of heart rate variability, and (3) whether well-characterized somatic activating mutations in the stimulatory G protein, G alpha s, underlie RMVT. Twelve patients with RMVT underwent electrophysiological study. Sustained monomorphic VT was reproducibly initiated and terminated with programmed stimulation and/or isoproterenol infusion in 11 of the 12 patients (the other patient had incessant RMVT). Induction of VT demonstrated cycle length dependence and was facilitated by rapid atrial or ventricular pacing. Termination of VT occurred in response to interventions that either lowered stimulated levels of intracellular cAMP (and thus decreased intracellular Ca2+)--ie, adenosine (12 of 12), vagal maneuvers or edrophonium (8 of 9), and beta-blockade (3 of 5)--or directly decreased the slow-inward calcium current--ie, verapamil (10 of 12). Analysis of heart rate variability during 24-hour ambulatory monitoring in 7 patients showed that the sinus heart rate is increased and accelerates before nonsustained VT (P < .05), whereas high-frequency heart rate variability is unchanged. These findings are consistent with transient increases in sympathetic tone preceding nonsustained VT. Finally, myocardial biopsy samples were obtained from the site of origin of the VT (typically the RVOT) and from the right ventricular apex from 9 patients. Genomic DNA was extracted from each biopsy sample, and three exons of G alpha s in which activating mutations have previously been described were amplified by polymerase chain reaction. All sequences from these regions were found to be identical to that of control. Although the arrhythmia occurs at rest, the constellation of findings in idiopathic VT that is characterized by RMVT is consistent with the mechanism of cAMP-mediated triggered activity. Therefore, the spectrum of VT resulting from this mechanism includes not only paroxysmal exercise-induced VT but also RMVT.

Tachycardias of Right Ventricular Origin

Ventricular tachycardia arising from the right ventricle usually has a left bundle branch morphology and occurs in a variety of disorders. Uhl's anomaly and right ventricular dysplasia may represent a spectrum of one disorder and are a cause of right heart dilatation, failure, and premature sudden death due to ventricular arrhythmias. Familial forms of the disorder may account for focal clustering in some geographic areas. Management should involve aggressive stratification of arrhythmia risk and may include medical, surgical, or device therapy. In contrast, the syndrome of right ventricular outflow tract tachycardia, including nonischemic exercise-induced and repetitive monomorphic ventricular tachycardia, is a more benign entity. Management often involves beta- and calcium channel blocking drugs or type IC antiarrhythmic drugs. Catheter ablation of the arrhythmia focus in the right ventricular outflow tract has been used in selected patients. In this syndrome the right ventricle is normal, and noninvasive testing as well as electrophysiologic studies can be helpful in distinguishing it from the more malignant right ventricular dysplasia. Ventricular arrhythmias may also be seen after right ventricular incision, as in surgical repair of tetralogy of Fallot and ventricular septal defects. Significant ventricular ectopy associated with an abnormal right ventricle (enlarged or depressed systolic function) is associated with an increased risk for sustained arrhythmia and sudden cardiac death in this group. The optimal indicator(s) of highest risk in these patients remains under investigation but will likely include electrophysiologic testing. Bifascicular block occurs commonly after repair of tetralogy of Fallot, but is usually benign. Isolated right ventricular infarction is rare. Most right ventricular arrhythmias associated with ischemia occur in the setting of iatrogenic catheter manipulation for pacing or hemodynamic monitoring. In conclusion, right ventricular arrhythmias involve an unusual and interesting group of clinical entities and appear to span the spectrum of arrhythmias mechanisms. A macroreentrant activation ring around the ventriculotomy scar may account for the arrhythmias following repair of tetralogy of Fallot. Microreentry at sites of morphologic abnormalities results in the arrhythmias associated with right ventricular dysplasia and ischemia. Triggered activity related to DADs or, less likely, abnormal automaticity, produce repetitive monomorphic ventricular tachycardia and nonischemic exercise-induced ventricular tachycardia, both of which usually originate from the right ventricular outflow tract. Iatrogenic ventricular tachycardia associated with catheter manipulation is especially likely to occur in the presence of right ventricular ischemia and infarction. It is important to recognize these clinical entities because treatment is specific.(ABSTRACT TRUNCATED AT 400 WORDS)

Repetitive Monomorphic Ventricular Tachycardia in a 4‐Year‐Old Boy with Toxic Multinodular Goiter

A case of toxic multinodular goiter associated with repetitive monomorphic ventricular tachycardia (VT) is reported. A 4-year-old boy was found to have asymptomatic VT. When treatment with antiarrhythmic agents turned out to be ineffective, thyrotoxicosis was suspected due to the rapid enlargement of the left thyroid gland and associated thyroid function studies. A diagnosis of toxic multinodular goiter was made on the basis of subsequent scintigraphy and ultrasonography. Treatment with antithyroid drugs and inorganic iodine restored the thyroid function to normal, and was accompanied by the disappearance of VT. A left thyroid lobectomy was performed, and the pathological findings were compatible with toxic multinodular goiter. After the operation, the patient was transiently hypothyroid and had no VT without medication. A review of the literature revealed no previously documented cases of VT with toxic multinodular goiter.

Clinical and electrophysiological characteristics of ventricular tachycardia in children with normal hearts

Characteristics of 18 patients with clinical ventricular tachycardia (VT) and normal hearts documented by physical examination, echocardiography, and angiocardiography were analyzed. There were 13 males and 5 females, aged 1 to 16 years (mean ± SD, 9.7 ± 4.8 years). Six patients had hemodynamic instability during VT and the other 12 patients were hemodynamically stable. Two patients (11%) presented with sustained VT and 16 (89%) with episodes of nonsustained VT at varying intervals (3 of 16 with repetitive monomorphic VT). Among 14 patients on whom exercise tests were performed, seven had exercise-induced VT. During electrophysiologic studies, VT was induced in 16 of 18 (89%) (in 13 patients with morphology identical to clinical VT). VT was induced by programmed stimulation (single, double, and burst stimulation of the right atrium or right ventricular apex during sinus rhythm or during pacind for eight beats) in 5 of 18 (28%) patients; with isoproterenol, VT was aggravated spontaneously in 6 of 15 (40%) patients; and during stimulation VT was induced in 8 of 15 (53%) patients. Among patients whose VT was not induced during programmed stimulation, VT was induced with the addition of isoproterenol in 11 of 12 (92%). All 14 patients in follow-up are in stable condition, seven patients with medication and seven without medication. Pediatric patients with normal hearts and clinically detected VT usually have VT induced by programmed stimulation, either with or without isoproterenol stimulation.

Torsade de Pointes and Other Pause‐Induced Ventricular Tachycardias: The Short‐Long‐Short Sequence and Early Afterdepolarizations

The early afterdepolarization, which is an interruption of repolarization, can evoke a second upstroke or a salvo of action potentials. It is suggested that the electrophysiological characteristics of the early afterdepolarization can produce a lengthening of the QT interval and that the second upstroke and salvo of activity that may follow, it can explain many features of torsade de pointes and of certain other ventricular tachycardias. The early afterdepolarization, torsade de pointes, and repetitive monomorphic idiopathic ventricular tachycardia are all induced by bradycardia or by a preceding long RR interal. The R-on-T phenomenon is also discussed.

Repetitive monomorphic ventricular tachycardia aborted by sleep

A 43-year-old woman with a 12-year history of palpitation was found to have recurrent monomorphic ventricular tachycardia resistent to beta-blockade but abolished by sleep.

Determinants of the spontaneous ectopic activity in repetitive monomorphic idiopathic ventricular tachycardia

Twenty-four hour ambulatory electrocardiographic tape recordings of 30 patients (16 men and 14 women, mean age 42 +/- 17 years) with repetitive monomorphic idiopathic ventricular tachycardia were analyzed using a new computerized system designed to study 15 RR cycles and mean heart rate of the 3 minutes preceding any defined event. The mean (+/- SD) number of events analyzed per patient in 24 hours was 610 +/- 483 for single premature ventricular complexes, 622 +/- 490 for couplets, 260 +/- 411 for runs of 3 complexes, 186 +/- 476 for runs of 4, 108 +/- 173 for runs of 5, 82 +/- 129 for runs of 6 to 10 and 83 +/- 116 for runs of more than 10 complexes. The heart rate was faster before runs of ventricular tachycardia than before isolated extrasystoles (p less than 0.01) and a positive linear correlation was observed between the mean preceding heart rate and the type of extrasystolic activity, the length of the runs increasing with increasing preceding heart rate (r = 0.98, p less than 0.001). A long RR interval just before the occurrence of runs was present in 77% of the cases (23 of 30) with or without an oscillatory pattern of RR intervals due to bigeminy or trigeminy, and the length of the runs correlated positively with the duration of this long preceding diastole (r = 0.90, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Repetitive, monomorphic ventricular tachycardia: Clinical and electrophysiologic characteristics in patients with and patients without organic heart disease

The clinical and electrophysiologic characteristics of 6 patients who had repetitive monomorphic ventricular tachycardia (VT) after a remote myocardial infarction (group A) were compared with those of 22 patients who had this arrhythmia without structural heart disease (group B). VT had a right bundle branch block morphologic pattern in 5 of 6 group A patients and a left bundle branch block morphologic pattern in all group B patients. Endocardial catheter activation mapping was performed in 4 group A patients and in 9 group B patients during VT. In all group A patients, the site of VT origin was on the border of the previous infarction; in all group B patients VT originated at the right ventricular outflow tract. Pacing and programmed stimulation induced VT in 5 of 6 group A patients and 7 of 22 group B patients (p = 0.03). Isoproterenol infusion provoked VT in 4 group A patients and 9 group B patients. Type I antiarrhythmic agents suppressed VT in 4 group A patients and in 14 group B patients, whereas propranolol suppressed VT in 3 of 3 group A patients tested and in 12 of 20 group B patients. Verapamil suppressed spontaneous VT in 1 group A patient and in 4 group B patients. During a mean follow-up of 19 months for group A and 40 months for group B, no patient had died suddenly or had cardiac arrest.

Clinical and electrophysiologic findings in patients with repetitive monomorphic ventricular tachycardia and otherwise normal electrocardiogram

Natural history, structural substrate, electrocardiographic and electrophysiologic characteristics and therapy were evaluated in 18 patients who demonstrated repetitive ventricular tachycardia, defined as repeated episodes of ventricular tachycardia that had a uniform QRS configuration and normal sinus-conducted QRS complexes between the episodes of tachycardia. The patients were young (mean age 37 years) and frequently had a long history of arrhythmia before this evaluation; only two patients had a history of syncope and six were completely asymptomatic. Fourteen patients had no evidence of underlying structural heart disease, three had mitral valve prolapse and one had congestive cardiomyopathy. Episodes of ventricular tachycardia tended to occur in clusters over a 24 hour electrocardiographic recording period. Repetitive ventricular tachycardia was induced in two of nine patients by programmed electrical stimulation, and in seven patients incremental atrial and ventricular pacing suppressed spontaneous arrhythmia. In the one patient whose tachycardia was induced by incremental ventricular pacing there was an inverse relation between pacing cycle length and the interval from the last paced complex to the first complex of ventricular tachycardia, indicating there was overdrive suppression. At a follow-up time of 0.5 to 8 years no patient had died or had worsening of symptoms. Encainide completely eliminated episodes of ventricular tachycardia during acute treatment in five of six patients tested. Seven patients received no antiarrhythmic therapy and the arrhythmia appeared to have spontaneously resolved in four of these patients. Repetitive ventricular tachycardia appears to have distinct clinical and electrophysiologic characteristics. In this series the arrhythmia had a good prognosis and often required no treatment. The electrophysiologic features are consistent with a mechanism of automaticity.