The QT and QS2 intervals in patients with mitral leaflet prolapse

Electromechanical Window and Spontaneous Ventricular Tachyarrhythmias in Takotsubo Syndrome

QT interval prolongation is common in patients hospitalized with Takotsubo syndrome (TTS), however, only a minority experience ventricular tachyarrhythmias. Our aim was to characterize the electromechanical window (EMW) in patients with TTS and to evaluate its association with ventricular tachyarrhythmias. We preformed aretrospective analysis of 84 patients hospitalized with TTS in the Tel-Aviv Medical Center between 2013 and 2022. All patients underwent a comprehensive echocardiographic evaluation and the EMW was calculated by subtracting the QT interval from the QRS onset to the aortic valve closure obtained from a continuous-wave Doppler for the same beat. Of the 84 patients with TTS, 74 (88%) were female and the mean age was 70 ± 11 years. The mean left ventricular ejection fraction was 42 ± 8%. The EMW was negative in 81 patients (96%), and the mean EMW was -69 ± 50 ms. Ventricular tachyarrhythmias occurred in 7 patients (8%). The EMW of patients who experienced ventricular tachyarrhythmias was more negative than patients who did not (-133 ± 23 ms vs -63 ± 48 ms, p = 0.001). In the univariate analysis, EMW and QT were associated with ventricular tachyarrhythmias (univariate odds ratio [OR]EMW 1.03, 95% confidence interval [CI] 1.01 to 1.05, p = 0.003 and univariate ORQTc 1.02, 95% CI 1.01 to 1.03, p = 0.02); however, only EMW remained significant in the multivariate analysis (OREMW 1.03 95% CI 1.03 to 1.05, p = 0.023). EMW was more effective than corrected QT interval in identifying patients who had ventricular tachyarrhythmias (AUCEMW: 0.89, 95% CI 0.82 to 0.97 vs AUCQTc 0.77, 95% CI 0.61 to 0.93, p = 0.02), and a cut-off value of -108 ms was predictive of ventricular tachyarrhythmias with a sensitivity of 86% and a specificity of 79%. In conclusion, EMW is negative in patients with TTS and is associated with increased risk for ventricular tachyarrhythmias. The role of EMW in the risk stratification of patients with TTS warrants further investigation.

Predictive Value of Electromechanical Window for Risk of Fatal Ventricular Arrhythmia

BACKGROUND

As an indicator of electro-mechanical coupling, electromechanical window (EMW) can be used to predict fatal ventricular arrhythmias. We investigated the additive effect of EMW on the prediction of fatal ventricular arrhythmias in high-risk patients.

METHODS

We included patients who had implantable cardioverter-defibrillator (ICD) implanted for primary or secondary prevention. The event group was defined as those who received an appropriate ICD therapy. We acquired echocardiograms at ICD implantation and follow-up. The EMW was calculated as the difference between the interval from QRS onset to aortic valve closure and QT interval from the electrocardiogram embedded in the continuous wave doppler image. We evaluated the predictive value of EMW for predicting fatal ventricular arrhythmia.

RESULTS

Of 245 patients (67.2 ± 12.8 years, 63.7% men), the event group was 20.0%. EMW at baseline (EMW-Baseline) and follow-up (EMW-FU) was significantly different between event and control groups. After adjustment, both EMW-Baseline (odds ratio [OR]_adjust 1.02 [1.01-1.03], P = 0.004) and EMW-FU (OR_adjust 1.06 [1.04-1.07], P < 0.001) remained as significant predictors for fatal arrhythmic events. Adding EMW-Baseline significantly improved the discriminating ability of the multivariable model including clinical variables (area under the curve [AUC] 0.77 [0.70-0.84] vs. AUC 0.72 [0.64-0.80], P = 0.004), while a univariable model using EMW-FU alone showed the best performance among models (AUC 0.87 [0.81-0.94], P = 0.060 against model with clinical variables; P = 0.030 against model with clinical variables and EMW-Baseline).

CONCLUSION

The EMW could effectively predict severe ventricular arrhythmia in ICD implanted patients. This finding supports the importance of incorporating the electro-mechanical coupling index into the clinical practice for predicting future fatal arrhythmia events.

Evaluating corrected carotid flow time as a non-invasive parameter for trending cardiac output and stroke volume in cardiac surgery patients

PURPOSE

The corrected carotid flow time (ccFT) is derived from a pulsed-wave Doppler signal at the common carotid artery. Several equations are currently used to calculate ccFT. Its ability to assess the intravascular volume status non-invasively has recently been investigated. The purpose of this study was to evaluate the correlation and trending ability of ccFT with invasive cardiac output (CO) and stroke volume (SV) measurements.

METHODS

Eighteen cardiac surgery patients were included in this prospective observational study. ccFT measurements were obtained at three time points: after induction of anesthesia (T1), after a passive leg raise (T2), and post-bypass (T3). Simultaneously, CO and SV were measured by calibrated pulse contour analysis. Three different equations (Bazett, Chambers, and Wodey) were used to calculate ccFT. The correlation and percentage change in time (concordance) between ccFT and CO and between ccFT and SV were evaluated.

RESULTS

Mean ccFT values differed significantly for the three equations (p < 0.001). The correlation between ccFT and CO and between ccFT and SV was highest for Bazett's (ρ = 0.43, p < 0.0001) and Wodey's (ρ = 0.33, p < 0.0001) equations, respectively. Concordance between ΔccFT and ΔCO and between ΔccFT and ΔSV was highest for Bazett's (100%) and Wodey's (82%) equations, respectively. Subgroup analysis demonstrated that correlation and concordance between SV and ccFT improved when assessed within limited heart rate (HR) ranges.

CONCLUSION

The use of different ccFT equations leads to variable correlation and concordance rates between ccFT and CO/SV measurements. Bazett's equation acceptably tracked CO changes in time, while the trending capability of SV was poor.

Relationship between life threatening events and electromechanical window in patients with hypertrophic cardiomyopathy: a novel parameter for risk stratification of sudden cardiac death Electromechanical window in patients with hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a leading cause of sudden cardiac death (SCD) in young individuals, largely due to ventricular arrhythmias, which may be associated with electrical disturbances from pathologic myocardial changes.

OBJECTIVES

We investigated electromechanical mismatches in patients with HCM and the relationship between electromechanical mismatches and life-threatening events (LTEs).

METHODS

We performed a retrospective review of patients diagnosed with HCM, aged 1-80 years old. Electromechanical mismatch was evaluated using the electromechanical window (EMW), defined as the interval between the Q wave and aortic valve closure minus the QT interval.

RESULTS

We enrolled 458 patients with a mean age of 52.4±18.8 years. When the EMW of patients with HCM was compared to that of age/sex-matched normal controls, the EMW was more negative in patients with HCM than in normal controls (-51±35 vs. 7±19 ms, p<0.001). LTEs occurred in 25 patients (5.5%). The EMW was more negative in patients with LTEs than in those without (-77±33 vs. -42±31 ms, p<0.001). The cut-off value of EMW to identify patients with LTEs was -54 ms and the c-index of EMW was 0.726. EMW<-54 ms, unexplained syncope, pediatric-onset, and extreme left ventricular hypertrophy were significant risk factors for LTEs on multivariate analysis.

CONCLUSIONS

EMW was more negative in patients with HCM than in healthy individuals, and profound EMW negativity was an independent risk factor for LTEs. EMW can be useful for the risk stratification of SCD in patients with HCM.

Diagnostic characteristics of 11 formulae for calculating corrected flow time as measured by a wearable Doppler patch

BACKGROUND

Change of the corrected flow time (Ftc) is a surrogate for tracking stroke volume (SV) in the intensive care unit. Multiple Ftc equations have been proposed; many have not had their diagnostic characteristics for detecting SV change reported. Further, little is known about the inherent Ftc variability induced by the respiratory cycle.

MATERIALS AND METHODS

Using a wearable Doppler ultrasound patch, we studied the clinical performance of 11 Ftc equations to detect a 10% change in SV measured by non-invasive pulse contour analysis; 26 healthy volunteers performed a standardized cardiac preload modifying maneuver.

RESULTS

One hundred changes in cardiac preload and 3890 carotid beats were analyzed. Most of the 11 Ftc equations studied had similar diagnostic attributes. Wodeys' and Chambers' formulae had identical results; a 2% change in Ftc detected a 10% change in SV with a sensitivity and specificity of 96% and 93%, respectively. Similarly, a 3% change in Ftc calculated by Bazett's formula displayed a sensitivity and specificity of 91% and 93%. Ftc_Wodey had 100% concordance and an R² of 0.75 with change in SV; these values were 99%, 0.76 and 98%, 0.71 for Ftc_Chambers and Ftc_Bazetts, respectively. As an exploratory analysis, we studied 3335 carotid beats for the dispersion of Ftc during quiet breathing using the equations of Wodey and Bazett. The coefficient of variation of Ftc during quiet breathing for these formulae were 0.06 and 0.07, respectively.

CONCLUSIONS

Most of the 11 different equations used to calculate carotid artery Ftc from a wearable Doppler ultrasound patch had similar thresholds and abilities to detect SV change in healthy volunteers. Variation in Ftc induced by the respiratory cycle is important; measuring a clinically significant change in Ftc with statistical confidence requires a large sample of beats.

Characteristics of electromechanical window in anesthetized rabbit models of short QT and long QT syndromes

The current regulatory guidelines recommend the use of QT interval to assess the risk of arrhythmogenic potential of new chemical entities. Recently, the electromechanical window (EMW), the difference in duration between electrical and mechanical systole, has been proposed as markers for drug-induced torsades de pointes (TdP); however, data of EMW in short QT model are not available. This study aimed to characterize the EMW as a marker for drug-induced ventricular arrhythmias in anesthetized rabbit model of long QT syndrome type 2 (LQT2) and short QT syndrome (SQTS) infused with reference compounds known to lengthen or shorten QT intervals. After rabbits were anesthetized with isoflurane, body surface electrocardiograms and left ventricular pressure were recorded. The LQT2 was produced by intravenous infusion with dofetilide (n = 6), quinidine (n = 6) and sotalol (n = 6) whereas the SQTS was induced by intravenous escalating concentrations of nicorandil (n = 7), pinacidil (n = 5) and cromakalim (n = 5). The EMW in anesthetized rabbits ranged from 1.3 to 53.3 msec. All three drugs known to lengthen QT intervals prolonged QT and QTcF interval while the EMW was markedly decreased to negative values. Pinacidil significantly produced QT and QTcF shortening and significantly abbreviated the EMW (p < 0.05). This study demonstrated that the EMW is associated with QT intervals (p < 0.001). It is negative in the presence of QT-prolonging drugs while it is more positive in the presence of QT-shortening drugs. The results suggest that the EMW in anesthetized rabbits can be used in drug safety evaluation in addition to the QT interval.

Role of abnormal repolarization in the mechanism of cardiac arrhythmia

In cardiac patients, life-threatening tachyarrhythmia is often precipitated by abnormal changes in ventricular repolarization and refractoriness. Repolarization abnormalities typically evolve as a consequence of impaired function of outward K⁺ currents in cardiac myocytes, which may be caused by genetic defects or result from various acquired pathophysiological conditions, including electrical remodelling in cardiac disease, ion channel modulation by clinically used pharmacological agents, and systemic electrolyte disorders seen in heart failure, such as hypokalaemia. Cardiac electrical instability attributed to abnormal repolarization relies on the complex interplay between a provocative arrhythmic trigger and vulnerable arrhythmic substrate, with a central role played by the excessive prolongation of ventricular action potential duration, impaired intracellular Ca²⁺ handling, and slowed impulse conduction. This review outlines the electrical activity of ventricular myocytes in normal conditions and cardiac disease, describes classical electrophysiological mechanisms of cardiac arrhythmia, and provides an update on repolarization-related surrogates currently used to assess arrhythmic propensity, including spatial dispersion of repolarization, activation-repolarization coupling, electrical restitution, TRIaD (triangulation, reverse use dependence, instability, and dispersion), and the electromechanical window. This is followed by a discussion of the mechanisms that account for the dependence of arrhythmic vulnerability on the location of the ventricular pacing site. Finally, the review clarifies the electrophysiological basis for cardiac arrhythmia produced by hypokalaemia, and gives insight into the clinical importance and pathophysiology of drug-induced arrhythmia, with particular focus on class Ia (quinidine, procainamide) and Ic (flecainide) Na⁺ channel blockers, and class III antiarrhythmic agents that block the delayed rectifier K⁺ channel (dofetilide).

Impact of hypokalemia on electromechanical window, excitation wavelength and repolarization gradients in guinea-pig and rabbit hearts

Normal hearts exhibit a positive time difference between the end of ventricular contraction and the end of QT interval, which is referred to as the electromechanical (EM) window. Drug-induced prolongation of repolarization may lead to the negative EM window, which was proposed to be a novel proarrhythmic marker. This study examined whether abnormal changes in the EM window may account for arrhythmogenic effects produced by hypokalemia. Left ventricular pressure, electrocardiogram, and epicardial monophasic action potentials were recorded in perfused hearts from guinea-pig and rabbit. Hypokalemia (2.5 mM K(+)) was found to prolong repolarization, reduce the EM window, and promote tachyarrhythmia. Nevertheless, during both regular pacing and extrasystolic excitation, the increased QT interval invariably remained shorter than the duration of mechanical systole, thus yielding positive EM window values. Hypokalemia-induced arrhythmogenicity was associated with slowed ventricular conduction, and shortened effective refractory periods, which translated to a reduced excitation wavelength index. Hypokalemia also evoked non-uniform prolongation of action potential duration in distinct epicardial regions, which resulted in increased spatial variability in the repolarization time. These findings suggest that arrhythmogenic effects of hypokalemia are not accounted for by the negative EM window, and are rather attributed to abnormal changes in ventricular conduction times, refractoriness, excitation wavelength, and spatial repolarization gradients.

The electro-mechanical window in anaesthetized guinea pigs: a new marker in screening for Torsade de Pointes risk

BACKGROUND AND PURPOSE

QT prolongation is commonly used as a surrogate marker for Torsade de Pointes (TdP) risk of non-cardiovascular drugs. However, use of this indirect marker often leads to misinterpretation of the realistic TdP risk, as tested compounds may cause QT prolongation without evoking TdP in humans. A negative electro-mechanical (E-M) window has recently been proposed as an alternative risk marker for TdP in a canine LQT1 model. Here, we evaluated the E-M window in anaesthetized guinea pigs as a screening marker for TdP in humans.

EXPERIMENTAL APPROACH

The effects of various reference drugs and changes in body temperature on the E-M window were assessed in instrumented guinea pigs. The E-M window was defined as the delay between the duration of the electrical (QT interval) and mechanical (QLVP(end) ) systole.

KEY RESULTS

Drugs with known TdP liability (quinidine, haloperidol, domperidone, terfenadine, thioridazine and dofetilide), but not those with no TdP risk in humans (salbutamol and diltiazem) consistently decreased the E-M window. Interestingly, drugs with known clinical QT prolongation, but with low risk for TdP (amiodarone, moxifloxacin and ciprofloxacin) did not decrease the E-M window. Furthermore, the E-M window was minimally affected by changes in heart rate or body temperature.

CONCLUSIONS AND IMPLICATIONS

A decreased E-M window was consistently observed with drugs already known to have high TdP risk, but not with drugs with low or no TdP risk. These results suggest that the E-M window in anaesthetized guinea pigs is a risk marker for TdP in humans.

The Electro-Mechanical window: a risk marker for Torsade de Pointes in a canine model of drug induced arrhythmias

BACKGROUND AND PURPOSE

In cardiovascular pharmacology, electrical and mechanical events can be distinguished, and the phrase 'electro-mechanical window' (EMw) describes the temporal difference between these events. We studied whether changes in EMw have potential predictive value for the occurrence of arrhythmias in fentanyl/etomidate-anaesthetized beagle (FEAB) dogs.

EXPERIMENTAL APPROACH

The EMw was calculated as differences between the QT interval and QLVP(end) in FEAB dogs during atrial pacing, treatment with isoprenaline or atropine, body temperature changes and induction of Torsade de Pointes (TdP) in an LQT1 model.

KEY RESULTS

The electrical systole (QT interval) was shorter than the duration of the mechanical event (QLVP(end) ), providing a positive EMw. Atrial pacing, atropine or body temperature changes had no major effects on EMw, despite large changes in QT duration. However, β-adrenoceptor stimulation (with isoprenaline) decreased the EMw (from 90 to 5 ms) and in combination with HMR1556, a blocker of the slowly activating potassium current (I(Ks) ), induced a large negative EMw (-109ms) and TdP. Prevention of TdP by atenolol or verapamil was associated with a less negative EMw (-23 to -16ms). Mexiletine, a poorly effective long QT treatment, did not affect the EMw or prevent TdP induction.

CONCLUSIONS AND IMPLICATIONS

The EMw is a marker, other than QT prolongation, of TdP risk in the FEAB model. Therefore, we suggest examining the EMw as a risk marker in cardiovascular safety studies and as a potential biomarker to improve clinical management of long QT syndrome patients, especially in patients with borderline QT prolongation.

Sudden adult death

In the investigation of sudden death in adults, channelopathies, such as long QT syndrome, have risen to the fore in the minds of forensic pathologists in recent years. Examples of these disorders are touched upon in this review as an absence of abnormal findings at postmortem examination is characteristic and the importance of considering the diagnosis lies in the heritable nature of these conditions. Typically, a diagnosis of a possible channelopathy is evoked as an explanation for a 'negative autopsy' in a case of apparent sudden natural death. However, the one potential adverse effect of this approach is that subtle causes of sudden death may be overlooked. The intention of this article is to review and discuss potential causes of sudden adult death (mostly natural) that should be considered before resorting to a diagnosis of possible channelopathy. Nonetheless, it becomes apparent that many of the potential causes of sudden death can have a genetic basis. Thus, it becomes an important consideration that there may be a genetic basis to sudden death that extends beyond the negative autopsy.

QT interval in anorexia nervosa

OBJECTIVES

To determine the incidence of a long QT interval as a marker for sudden death in patients with anorexia nervosa and to assess the effect of refeeding. To define a long QT interval by linear regression analysis and estimation of the upper limit of the confidence interval (95% CI) and to compare this with the commonly used Bazett rate correction formula.

DESIGN

Prospective case control study.

SETTING

Tertiary referral unit for eating disorders.

SUBJECTS

41 consecutive patients with anorexia nervosa admitted over an 18 month period. 28 age and sex matched normal controls.

MAIN OUTCOME MEASURES

maximum QT interval measured on 12 lead electrocardiograms.

RESULTS

43.6% of the variability in the QT interval was explained by heart rate alone (p < 0.00001) and group analysis contributed a further 5.9% (p = 0.004). In 6 (15%) patients the QT interval was above the upper limit of the 95% CI for the prediction based on the control equation (NS). Two patients died suddenly; both had a QT interval at or above the upper limit of the 95% CI. In patients who reached their target weights the QT interval was significantly shorter (median 9.8 ms; p = 0.04) relative to the upper limit of the 60% CI of the control regression line, which best discriminated between patients and controls. The median Bazett rate corrected QT interval (QTc) in patients and controls was 435 v 405 ms.s-1/2 (p = 0.0004), and before and after refeeding it was 435 v 432 ms.s1/2 (NS). In 14(34%) patients and three (11%) controls the QTc was > 440 ms.s-1/2 (p = 0.053).

CONCLUSIONS

The QT interval was longer in patients with anorexia nervosa than in age and sex matched controls, and there was a significant tendency to reversion to normal after refeeding. The Bazett rate correction formula overestimated the number of patients with QT prolongation and also did not show an improvement with refeeding.

QT prolongation on the electrocardiogram in diabetic autonomic neuropathy

Patients with Type 1 diabetes and autonomic neuropathy have an increased risk of sudden death for which the mechanism remains obscure. Prolongation of the QT interval on the electrocardiogram may occur with sympathetic dysfunction and is also associated with ventricular arrhythmia and sudden death. We have therefore measured the QT interval in patients with Type 1 diabetes with normal, borderline, and definitely abnormal autonomic function tests and in non-diabetic control subjects. The maximum QT interval was measured on 12-lead electrocardiograms recorded at rest and then plotted against the RR interval. The QT interval was above the upper 95% limit for the non-diabetic control subjects in 5 diabetic patients with abnormal autonomic function tests (33%), but in no cases with normal or borderline tests. Multivariate analysis confirmed that autonomic score contributed significantly (p less than 0.025) to the variance in QT interval. The raw Valsalva ratio alone also contributed significantly to the variance in QT interval (p = 0.025). Heart rate variability, heart rate response to standing, age, sex, and the presence of symptoms of autonomic neuropathy did not contribute significantly.

Exercise response in young women with mitral valve prolapse

To detect for possible evidence of autonomic nervous system dysfunction, we assessed exercise response in 198 young women with echocardiographically documented MVP. The same test was used to determine whether patients with or without physical symptoms or with various auscultatory findings responded differently. Compared with 105 age- and sex-matched healthy subjects, the MVP patients showed significantly higher mean heart rate, systolic blood pressure, pulse pressure and rate-pressure (double) product, at both rest and exercise; significantly lower mean near-maximal physical working capacity (PWC170); significantly higher incidence of both arrhythmias and nonspecific ST and T wave changes; and a significantly longer mean corrected QT interval. None of these findings was associated with the presence of physical symptoms or with specific auscultatory or echocardiographic findings. These observations strongly suggest an autonomic nervous system imbalance in some young women with MVP, irrespective of whether physical symptoms are present.

The effects of probucol on QT/QS2 relation and systolic time intervals

The QT, QTc, QS2 intervals, pre-ejection period-left ventricular ejection time ratios and serum lipoprotein levels were measured in 8 patients with primary hypercholesterolemia before and after a 3-month therapy with probucol, 1 g/day. Both QT and QTc intervals increased significantly, whereas no significant changes were observed between the pre- and post-treatment QT/QS2 and pre-ejection period-left ventricular ejection time ratios. These results help to explain why treatment with probucol, while effecting a prolongation of the QTc interval, does not result in serious arrhythmias in man.