Paradoxical QRST integral changes with ventricular repolarization dispersion

Body surface QRST integral (QRSTI) maps have been shown theoretically to reflect disparity of intrinsic repolarization properties and have been experimentally linked to increased arrhythmia susceptibility. Paradoxically, a lower magnitude of QRSTI in patients with heart disease and at risk for arrhythmias has been reported. We hypothesized that this paradoxical reduction in QRST magnitude is a consequence of increased heterogeneity of repolarization gradients in normal hearts. We generated QRSTI using a previously published heart model to compare QRSTI for aligned and random repolarization gradients. The heart model consisted of 50,000 cubic units in an anatomically correct arrangement that included parameters to simulate anisotropic conduction and inhomogeneous distribution of refractoriness. Body surface potential maps (BSPMs) were generated on a torso surface assuming a homogeneous torso and using the boundary element method for normal alignment of repolarization gradients and spatially reassigned repolarization values that randomized repolarization directions. QT duration was measured by the subtraction of Q onset time from T offset time on the BSPM. T offset was defined as the last potential to be detected at intervals of 3 ms that was above the threshold of 0.1 mV during recovery. The time of T offset showed a consistent tendency to shift to the left posterior and to split. When slow conduction velocities were assigned, BSPMs showed delayed propagation and multiple extrema. QRSTI showed systematic magnitude decrease with increasing randomness of repolarization gradient direction. Ventricular fibrillation (VF) could be induced by successive extrastimuli under the conditions of over 70% deviation and slow conduction of 0.5 m/s for the longitudinal direction. In conclusion, a possible explanation for the paradoxical reduction in QRSTI in the presence of constant repolarization disparity is the change in alignment of repolarization gradients.     

Facilitation of ventricular tachyarrhythmia induction by isoproterenol

Ventricular tachyarrhythmia induction was facilitated during infusion of isoproterenol in 21 of 60 patients with ventricular tachycardia (VT) or ventricular fibrillation (VF) in whom programmed electrical stimulation alone failed to reproducibly induce sustained ventricular tachyarrhythmias. Of 44 patients with no ventricular tachyarrhythmias induced before isoproterenol infusion, 11 had a sustained ventricular tachyarrhythmia and 1 patient had unsustained VT induced by isoproterenol alone or by programmed stimulation during the infusion. In 9 of 16 patients in whom nonreproducible or unsustained ventricular tachyarrhythmias were induced before isoproterenol infusion, more reproducible or more sustained ventricular tachyarrhythmias were induced during the infusion. Tachyarrhythmia induction was facilitated by isoproterenol in 20 of 40 patients with sustained VT clinically, but in only 1 of 20 patients with unsustained VT or VF clinically. Among patients with sustained VT clinically, those with exercise-provoked VT and those who had not been tested with stimulation at a second right ventricular site or in the left ventricle were more likely to have induction facilitated by isoproterenol. Drugs effective against induction of isoproterenol-facilitated ventricular tachyarrhythmias were identified in 13 of 25 trials. These drugs were effective during a mean follow-up of 17 months in 7 of 9 long-term trials.     

The case of the QRS-T angles versus QRST integral maps

This contribution discusses the QRS-T angle as well as the QRST integral map. Both of these topics have been tested in their application in extracting the major features of depolarization and repolarization: their spatio-temporal behaviour, and how much of their global or local nature might be deduced from signals that can be observed clinically. Recently, it is in particular the QRS-T angle that has received considerable attention, a method that stems directly from vectorcardiography, a subdomain of electrocardiography. The QRST integral map is a display of a map on the body surface of the integrals over time of the ECG signals observed at sets of electrodes. The common biophysical background of both techniques is highlighted. In particular it is explained why, in healthy myocardium, both provide a similar view on the global timing of the depolarization and repolarization of all cardiac myocytes, more specifically, on the dispersion of their action potential durations. In the presence of ischemia, the view obtained is of the integral over time of the transmembrane potentials, which comprises a 'mixture' of their timing and magnitude. The analysis of results of a simulation study emphasizes the large discrepancies that may be observed between the QRS-T angle in the frontal plane and its 3D variant. It is shown that the required vector representation of the signals may be derived from the 12-lead ECG by using the transfer matrix proposed in 1990 by Kors and colleagues.     

Encainide for refractory ventricular tachyarrhythmia

Encainide, a new antiarrhythmic agent, was studied in 80 patients with sustained ventricular tachycardia or ventricular fibrillation. Drug efficacy was evaluated by ambulatory monitoring and exercise testing in 63 patients who had frequent or repetitive ventricular premature beats and by means of electrophysiologic testing in 17 patients who did not have significant arrhythmia during a 48-hour control period. Encainide was effective in 36 of 63 patients (57%) as judged by ambulatory monitoring and in 35 of 51 patients (69%) who had exercise tests while taking the drug. Overall, 34 patients (54%) responded to encainide when evaluated by both monitoring and exercise testing. The drug was effective in 7 of 16 patients (44%) who underwent electrophysiologic studies. Daily doses and blood levels of encainide were Comparable in responders and nonresponders. Toxicity occurred in 24 patients (30%) and included nausea, vomiting, headaches, lethargy, tremors and conduction disturbances. In 18 patients (23%) arrhythmia was aggravated. An increase in arrhythmia correlated with larger daily doses of encainide and higher serum blood levels of encainide and its metabolite OD-methyl-encainide, but did not correlate with QRS- or QT-interval widening. Of the 27 patients who were discharged on encainide, 23 were maintained on the drug for an average of 21 months (range 12 to 44). Three patients died suddenly.Thus, encainide is a useful agent for suppression of malignant ventricular arrhythmias. However, it has a high potential for worsening arrhythmias and careful evaluation by both monitoring and exercise testing is necessary to judge its effect.     

室性心动过速的导管消融治疗

室性心动过速（ventricular tachycardia．VT）简称室速,指起源于希氏束分支以下部位的室性快速心律,频率〉100次／min。室速持续30S以上或因严重的血流动力学障碍而需立即终止者,称持续性室速。室速可分为器质性心脏病室速和非器质性心脏病室速．前者是指发生于有器质性心脏病证据患者的室速,如冠心病、心肌病、心脏瓣膜病、心肌炎、致心律失常性右室发育不良、长QT综合征以及各种心脏外科手术后等。临床上以冠心病,特别是心肌梗死后室速最为多见。非器质性心脏病室速又称特发性室速。是指发生于利用目前诊断技术未能查出患者有器质性心脏病证据的室速,     

Traumatic heart block and tachyarrhythmia induced by right ventricular impact

The effect of direct impact on the right ventricle was investigated in an anesthetized open-chest canine preparation. At each of five impact sites, direct local loading produced immediate ventricular asystole followed by varying degrees of AV conduction block, lasting 70 +/- 35 seconds. Sinus rhythm temporarily resumed in most cases for 30 +/- 25 seconds before ventricular tachycardia abruptly intervened for 150 +/- 70 seconds. Recovery to sinus rhythm usually followed the ventricular tachycardia. Impact over the ventricular aspect supplied by the right coronary artery above the conduction bundle branches caused a longer period of asystole than impact over other sites. The duration of the delayed tachyarrhythmia was independent of impact site. Denervation of the heart did not influence the conduction block or the tachyarrhythmia. Intravenous injection of propranolol (1.6 mg/kg) did not affect the immediate conduction block but prevented the ventricular tachycardia.     

Cardiac resynchronization therapy and ventricular tachyarrhythmia burden

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Lorcainide in patients with refractory ventricular tachyarrhythmia

Lorcainide, a new antiarrhythmic agent with local anesthetic or membrane-stabilizing properties similar to those of quinidine, was tested in 76 patients with diverse types of heart disease and recurrent ventricular tachycardia or ventricular fibrillation. Lorcainide was administered for 72 to 96 hours in a dose ranging from 200 to 400 mg daily. Evaluation of drug efficacy involved ambulatory monitoring and exercise stress testing in 60 patients who had high grade ventricular arrhythmia. Invasive electrophysiologic testing was carried out in the remaining 16 patients who exhibited infrequent ventricular ectopic activity during control studies. Lorcainide was effective in 21 (38%) of 56 patients evaluated for suppression of ventricular ectopic activity and in 6 (40%) of 15 who had invasive testing. In five patients, the drug was discontinued because of toxic reactions. Thus, 27 (38%) of the 71 patients who completed the drug study responded to lorcainide. Side effects, reported by 42 patients (55.3%), consisted primarily of insomnia and gastrointestinal symptoms; 7 experienced aggravation of arrhythmia. Fifteen patients were discharged while receiving lorcainide therapy, but in four the treatment was discontinued after 2 months because of side effects. Three patients died, one suddenly. It is concluded that lorcainide is of value in a small subset of patients with life-threatening ventricular arrhythmias who have proven refractory to conventional drugs. Its usefulness is limited by the high frequency of insomnia.     

Identification of susceptibility to ventricular tachycardia after myocardial infarction by nondipolarity of QRST area maps

The QRST area map has been related to susceptibility to ventricular tachyarrhythmias because it reflects the disparity of ventricular recovery properties. However, the clinical value of the nondipolarity of the QRST area map, a marker of nonuniform ventricular repolarization, has not been fully studied in myocardial infarction. The nondipolarity of the QRST area map (residue), the ratio of minimized deviation by an optimal dipole to the total measured potentials, was quantitatively studied in relation to susceptibility to ventricular tachycardia after myocardial infarction. The residue of the QRST area map was higher in 59 patients with myocardial infarction than in 44 normal subjects (25.0 +/- 9.0 versus 17.8 +/- 3.3%, p less than 0.01). Seventeen patients with ventricular tachycardia in the chronic phase (greater than 10 days) of myocardial infarction showed higher residue in their QRST area map (34.5 +/- 10.3%) than that in 29 patients without ventricular tachycardia throughout the study (22.7 +/- 6.7%) or that in 13 patients with ventricular tachycardia only in the acute phase (21.2 +/- 7.5%). QRST area maps with a residue greater than or equal to 25% (mean + 2 SD of normal subjects) identified patients with ventricular tachycardia in the chronic phase of myocardial infarction with a sensitivity of 82% and a specificity of 71%. These results suggest that quantitative assessment of the nondipolarity of the QRST area map is clinically useful for identifying susceptibility to ventricular tachycardia in the chronic phase of myocardial infarction.     

Large dose procainamide therapy for ventricular tachyarrhythmia

The efficacy and toxicity of large dose procainamide therapy (500 to 1,500 mg given orally every 4 hours) for recurrent ventricular tachyarrhythmla were examined in 35 patients referred for electrophysiologic evaluation. In 16 patients procainamide was determined by programmed ventricular stimulation and serial drug testing to be the most effective agent. A long-term oral regimen was begun followed by periodic clinical evaluation and 24 hour ambulatory electrocardlographic monitoring for recurrence of symptomatic arrhythmia. In all 16 patients drug efficacy, acutely, correlated with specific plasma drug levels, which averaged 13.6 ± 8.6 μg/ml (mean ± standard deviation). Dose-dependent effects of procainamide at lower than the acute effective level were observed in six patients and included progressive slowing of the tachycardia and increasing ease of arrhythmia induction. In 14 of 16 patients, efficacy of the long-term oral regimen correlated with the acute effective plasma level. All 11 patients with plasma concentrations maintained at or above the acute effective plasma level have been free of symptomatic arrhythmia for up to 48 months, whereas all five patients with concentrations below the acute effective plasma level have had early symptomatic recurrences. Manifestations of acute toxicity, including hypotension, excessive Q-T prolongation or progression of infranodal conduction disturbances, were not observed. Chronic toxicity was limited to gastrointestinal disturbances in two patients (12.5 percent) and drug-induced lupus erythematosus in four (25 percent). It is concluded that large dose procainamide therapy is quite effective in the treatment of recurrent inducible ventricular tachyarrhythmia, and that the improved efficacy over small dose therapy may be achieved without an increased incidence of toxic side effects.     

Noninvasive evaluation of indecainide for serious ventricular tachyarrhythmia

Indecainide, a new class 1C agent, was administered to 16 patients with a history of ventricular fibrillation or ventricular tachycardia. Evaluation of drug effect consisted of acute testing with 125 mg followed by a period of maintenance therapy. Efficacy, as evaluated with both ambulatory monitoring and exercise testing, was defined as total elimination of runs of ventricular tachycardia, greater than 90% reduction in couplets and greater than 50% decrease in ventricular premature complex. During acute drug testing 9 of the 16 patients responded to the drug. Four patients did not receive maintenance therapy with indecainide, because of toxic side effects. Of the remaining 12 patients, 7 responded to indecainide based on monitoring, 5 responded judged by exercise testing and 4 when both monitoring and exercise testing were considered. There was no correlation between dose, blood level of drug and effect on arrhythmia. In this small group acute drug testing did not appear to predict the response to the drug during maintenance therapy. Neurologic side effects were reported by 5 patients. Aggravation of arrhythmia occurred in 5 patients, 3 of whom had this complication during acute drug testing and 2 during maintenance therapy. Left ventricular ejection fraction, measured before and during therapy, decreased from an average of 43% to 35% (p less than 0.005). A reduction was observed irrespective of baseline left ventricular function. Indecainide is an effective antiarrhythmic agent in a small number of highly selected patients with serious ventricular arrhythmia, but potentially serious side effects limit its usefulness.     

Taser-induced rapid ventricular myocardial capture demonstrated by pacemaker intracardiac electrograms

Introduction : A Taser weapon is designed to incapacitate violent individuals by causing temporary neuromuscular paralysis due to current application. We report the first case of a Taser application in a person with a dual-chamber pacemaker demonstrating evidence of Taser-induced myocardial capture.
Methods and Results : Device interrogation was performed in a 53-year-old man with a dual-chamber pacemaker who had received a Taser shot consisting of two barbs delivered simultaneously. Assessment of pacemaker function after Taser application demonstrated normal sensing, pacing thresholds, and lead impedances. Stored event data revealed two high ventricular rate episodes corresponding to the exact time of the Taser application.
Conclusions: This report describes the first human case of ventricular myocardial capture at a rapid rate resulting from a Taser application. This raises the issue as to whether conducted energy devices can cause primary myocardial capture or capture only in association with cardiac devices providing a preferential pathway of conduction to the myocardium.     

Ventricular aneurysmectomy for the treatment of recurrent ventricular tachyarrhythmia

Resection of a left ventricular aneurysm led to termination of lifethreatening paroxysmal ventricular tachycardia in 2 patients. Preoperative cardiac catheterization and cineangiocardiography are essential for visualization of the aneurysm and mural thrombus. Our living patient has survived over 58 months after aneurysmectomy without recurrence of tachyarrhythmias and is receiving no medication. It is suggested that aneurysmectomy, preferably on an elective basis, may be indicated in the management of recurrent tachyarrhythmias even in the absence of congestive heart failure and systemic embolization.