Milton E. Guevara-Valdivia

The Response of the QT Interval to the Brief Tachycardia Provoked by Standing: A Bedside Test for Diagnosing Long QT Syndrome

OBJECTIVES This study was undertaken to determine whether the short-lived sinus tachycardia that occurs during standing will expose changes in the QT interval that are of diagnostic value. BACKGROUND The QT interval shortens during heart rate acceleration, but this response is not instantaneous. We tested whether the transient, sudden sinus tachycardia that occurs during standing would expose abnormal QT interval prolongation in patients with long QT syndrome (LQTS). METHODS Patients (68 with LQTS [LQT1 46%, LQT2 41%, LQT3 4%, not genotyped 9%] and 82 control subjects) underwent a baseline electrocardiogram (ECG) while resting in the supine position and were then asked to get up quickly and stand still during continuous ECG recording. The QT interval was studied at baseline and during maximal sinus tachycardia, maximal QT interval prolongation, and maximal QT interval stretching. RESULTS In response to brisk standing, patients and control subjects responded with similar heart rate acceleration of 28 +/- 10 beats/min (p = 0.261). However, the response of the QT interval to this tachycardia differed: on average, the QT interval of controls shortened by 21 +/- 19 ms whereas the QT interval of LQTS patients increased by 4 +/- 34 ms (p < 0.001). Since the RR interval shortened more than the QT interval, during maximal tachycardia the corrected QT interval increased by 50 +/- 30 ms in the control group and by 89 +/- 47 ms in the LQTS group (p < 0.001). Receiver-operating characteristic curves showed that the test adds diagnostic value. The response of the QT interval to brisk standing was particularly impaired in patients with LQT2. CONCLUSIONS Evaluation of the response of the QT interval to the brisk tachycardia induced by standing provides important information that aids in the diagnosis of LQTS.

Quinidine, A Life-Saving Medication for Brugada Syndrome, Is Inaccessible in Many Countries

OBJECTIVES The aim of this study was to determine the availability of quinidine throughout the world. BACKGROUND Quinidine is the only oral medication that is effective for preventing life-threatening ventricular arrhythmias due to Brugada syndrome and idiopathic ventricular fibrillation. However, because of its low price and restricted indication, this medication is not marketed in many countries. METHODS We conducted a survey of the availability of quinidine by contacting professional medical societies and arrhythmia specialists worldwide. Physicians were e-mailed questionnaires requesting information concerning the quinidine preparation available at their hospital. We also requested information concerning cases of adverse arrhythmic events resulting from unavailability of quinidine. RESULTS A total of 273 physicians from 131 countries provided information regarding the availability of quinidine. Quinidine was readily available in 19 countries (14%), not accessible in 99 countries (76%), and available only through specific regulatory processes that require 4 to 90 days for completion in 13 countries (10%). We were able to gather information concerning 22 patients who had serious arrhythmias probably related (10 cases) or possibility related (12 cases) to the absence of quinidine, including 2 fatalities possibly attributable to the unavailability of quinidine. CONCLUSIONS The lack of accessibility of quinidine is a serious medical hazard at the global level.

Female gender as independent risk factor of torsades de pointes during acquired atrioventricular block

BACKGROUND Female gender increases the risk of torsades de pointes (TdP) in the long QT syndrome, and this increased risk is assumed to be due to their longer QT interval. OBJECTIVE The purpose of this study was to study the interplay between gender, duration of the QT interval, and risk of TdP during AV block. METHODS We studied 250 patients (48% women) with AV block. QT interval was measured at the time of most severe bradycardia. We then constructed different receiver operating characteristic curves for the QTc of males and females for predicting TdP. RESULTS As expected, patients with TdP had longer QTc intervals than did patients with uncomplicated AV block (564 ± 81 ms vs 422 ± 62 ms, P < .001). This correlation between longer QTc and higher risk of TdP was true for both genders. However, the QT of females with TdP was shorter than the respective value for males with TdP. Despite similar severity of bradycardia, the QT was shorter for females (QT 672 ± 88 ms vs 727 ± 57 ms for females with TdP vs males with TdP, P = .022). The QTc/TdP risk curve for females was shifted to the left in comparison to the pertinent graph for males. Female gender was an independent predictor of TdP. CONCLUSION Women are at increased risk for developing TdP during AV block, but this increased risk is independent of their longer QT interval. Females develop TdP with QT intervals that are not necessarily arrhythmogenic for males.

Long QT syndrome complicating atrioventricular block: arrhythmogenic effects of cardiac memory.

Background— The magnitude of QT prolongation in response to bradycardia, rather than the bradycardia per se, determines the risk for torsade de pointes during atrioventricular block (AVB). However, we do not know why some patients develop more QT prolongation than others, despite similar bradycardia. We hypothesized that in patients who develop significant QRS vector changes during AVB, the effects of cardiac memory lead to excessive QT prolongation. Methods and Results— We studied 91 patients who presented with AVB and who also had an ECG predating the bradyarrhythmia for comparison. We correlated changes in QRS morphology and axis taking place during AVB with the bradycardia-induced QT prolongation. Patients with and without QRS morphology changes at the time of AVB were of similar age and sex. Moreover, despite similar R-R interval during AVB, cases with a QRS morphology change had significantly longer QT (648±84 versus 561±84; P <0.001) than those without. Patients who developed a change in QRS morphology at the time of AVB had a 7-fold higher risk of developing long QT. This risk nearly doubled when the change in QRS morphology was accompanied by a change in QRS axis. Conclusions— Cardiac memory resulting from a change in QRS morphology during AVB is independently associated with QT prolongation and may be arrhythmogenic during AVB.Background—The magnitude of QT prolongation in response to bradycardia, rather than the bradycardia per se, determines the risk for torsade de pointes during atrioventricular block (AVB). However, we do not know why some patients develop more QT prolongation than others, despite similar bradycardia. We hypothesized that in patients who develop significant QRS vector changes during AVB, the effects of cardiac memory lead to excessive QT prolongation. Methods and Results—We studied 91 patients who presented with AVB and who also had an ECG predating the bradyarrhythmia for comparison. We correlated changes in QRS morphology and axis taking place during AVB with the bradycardia-induced QT prolongation. Patients with and without QRS morphology changes at the time of AVB were of similar age and sex. Moreover, despite similar R-R interval during AVB, cases with a QRS morphology change had significantly longer QT (648±84 versus 561±84; P<0.001) than those without. Patients who developed a change in QRS morphology at the time of AVB had a 7-fold higher risk of developing long QT. This risk nearly doubled when the change in QRS morphology was accompanied by a change in QRS axis. Conclusions—Cardiac memory resulting from a change in QRS morphology during AVB is independently associated with QT prolongation and may be arrhythmogenic during AVB.

Radiofrequency ablation of atrioventricular accessory pathways associated with discordant atrioventricular connections.

Discordant atrioventricular connections associated with Wolff-Parkinson-White syndrome increase the challenge of radiofrequency ablation. We report the results and techniques of radiofrequency ablation in three patients with discordant atrioventricular connections, including one patient having double outlet right ventricle with atrioventricular reentry tachycardias. There were two males and one female, aged 14 and 22 years old. We found four accessory pathways during our electrophysiological studies, with two of them manifest on the electrocardiogram, corresponding to left paraseptal and right midseptal regions. The electrophysiological study confirmed this localization, and showed two concealed accessory pathways in the right and left paraseptal regions. Radiofrequency ablation was successful in all cases without recurrence at a mean follow-up of 18.6 months. No complications were observed during the procedures. We conclude that radiofrequency ablation is feasible and effective in the ablation of accessory pathways in patients with discordant atrioventricular connections.

Long QT Syndrome Complicating Atrioventricular BlockCLINICAL PERSPECTIVE: Arrhythmogenic Effects of Cardiac Memory

Background— The magnitude of QT prolongation in response to bradycardia, rather than the bradycardia per se, determines the risk for torsade de pointes during atrioventricular block (AVB). However, we do not know why some patients develop more QT prolongation than others, despite similar bradycardia. We hypothesized that in patients who develop significant QRS vector changes during AVB, the effects of cardiac memory lead to excessive QT prolongation. Methods and Results— We studied 91 patients who presented with AVB and who also had an ECG predating the bradyarrhythmia for comparison. We correlated changes in QRS morphology and axis taking place during AVB with the bradycardia-induced QT prolongation. Patients with and without QRS morphology changes at the time of AVB were of similar age and sex. Moreover, despite similar R-R interval during AVB, cases with a QRS morphology change had significantly longer QT (648±84 versus 561±84; P <0.001) than those without. Patients who developed a change in QRS morphology at the time of AVB had a 7-fold higher risk of developing long QT. This risk nearly doubled when the change in QRS morphology was accompanied by a change in QRS axis. Conclusions— Cardiac memory resulting from a change in QRS morphology during AVB is independently associated with QT prolongation and may be arrhythmogenic during AVB.Background—The magnitude of QT prolongation in response to bradycardia, rather than the bradycardia per se, determines the risk for torsade de pointes during atrioventricular block (AVB). However, we do not know why some patients develop more QT prolongation than others, despite similar bradycardia. We hypothesized that in patients who develop significant QRS vector changes during AVB, the effects of cardiac memory lead to excessive QT prolongation. Methods and Results—We studied 91 patients who presented with AVB and who also had an ECG predating the bradyarrhythmia for comparison. We correlated changes in QRS morphology and axis taking place during AVB with the bradycardia-induced QT prolongation. Patients with and without QRS morphology changes at the time of AVB were of similar age and sex. Moreover, despite similar R-R interval during AVB, cases with a QRS morphology change had significantly longer QT (648±84 versus 561±84; P<0.001) than those without. Patients who developed a change in QRS morphology at the time of AVB had a 7-fold higher risk of developing long QT. This risk nearly doubled when the change in QRS morphology was accompanied by a change in QRS axis. Conclusions—Cardiac memory resulting from a change in QRS morphology during AVB is independently associated with QT prolongation and may be arrhythmogenic during AVB.

Long QT Syndrome Complicating Atrioventricular BlockCLINICAL PERSPECTIVE

Background— The magnitude of QT prolongation in response to bradycardia, rather than the bradycardia per se, determines the risk for torsade de pointes during atrioventricular block (AVB). However, we do not know why some patients develop more QT prolongation than others, despite similar bradycardia. We hypothesized that in patients who develop significant QRS vector changes during AVB, the effects of cardiac memory lead to excessive QT prolongation. Methods and Results— We studied 91 patients who presented with AVB and who also had an ECG predating the bradyarrhythmia for comparison. We correlated changes in QRS morphology and axis taking place during AVB with the bradycardia-induced QT prolongation. Patients with and without QRS morphology changes at the time of AVB were of similar age and sex. Moreover, despite similar R-R interval during AVB, cases with a QRS morphology change had significantly longer QT (648±84 versus 561±84; P <0.001) than those without. Patients who developed a change in QRS morphology at the time of AVB had a 7-fold higher risk of developing long QT. This risk nearly doubled when the change in QRS morphology was accompanied by a change in QRS axis. Conclusions— Cardiac memory resulting from a change in QRS morphology during AVB is independently associated with QT prolongation and may be arrhythmogenic during AVB.Background—The magnitude of QT prolongation in response to bradycardia, rather than the bradycardia per se, determines the risk for torsade de pointes during atrioventricular block (AVB). However, we do not know why some patients develop more QT prolongation than others, despite similar bradycardia. We hypothesized that in patients who develop significant QRS vector changes during AVB, the effects of cardiac memory lead to excessive QT prolongation. Methods and Results—We studied 91 patients who presented with AVB and who also had an ECG predating the bradyarrhythmia for comparison. We correlated changes in QRS morphology and axis taking place during AVB with the bradycardia-induced QT prolongation. Patients with and without QRS morphology changes at the time of AVB were of similar age and sex. Moreover, despite similar R-R interval during AVB, cases with a QRS morphology change had significantly longer QT (648±84 versus 561±84; P<0.001) than those without. Patients who developed a change in QRS morphology at the time of AVB had a 7-fold higher risk of developing long QT. This risk nearly doubled when the change in QRS morphology was accompanied by a change in QRS axis. Conclusions—Cardiac memory resulting from a change in QRS morphology during AVB is independently associated with QT prolongation and may be arrhythmogenic during AVB.