The mode of onset of ventricular tachycardia. A patient-specific phenomenon

Enhancing the performance of premature ventricular contraction detection in unseen datasets through deep learning with denoise and contrast attention module

Premature ventricular contraction (PVC) is a common and harmless cardiac arrhythmia that can be asymptomatic or cause palpitations and chest pain in rare instances. However, frequent PVCs can lead to more serious arrhythmias, such as atrial fibrillation. Several PVC detection models have been proposed to enable early diagnosis of arrhythmias; however, they lack reliability and generalizability due to the variability of electrocardiograms across different settings and noise levels. Such weaknesses are known to aggravate with new data. Therefore, we present a deep learning model with a novel attention mechanism that can detect PVC accurately, even on unseen electrocardiograms with various noise levels. Our method, called the Denoise and Contrast Attention Module (DCAM), is a two-step process that denoises signals with a convolutional neural network (CNN) in the frequency domain and attends to differences. It focuses on differences in the morphologies and intervals of the remaining beats, mimicking how trained clinicians identify PVCs. Using three different encoder types, we evaluated 1D U-Net with DCAM on six external test datasets. The results showed that DCAM significantly improved the F1-score of PVC detection performance on all six external datasets and enhanced the performance of balancing both the sensitivity and precision of the models, demonstrating its robustness and generalization ability regardless of the encoder type. This demonstrates the need for a trainable denoising process before applying the attention mechanism. Our DCAM could contribute to the development of a reliable algorithm for cardiac arrhythmia detection under real clinical electrocardiograms.

Premature ventricular complexes and the risk of incident stroke: the Atherosclerosis Risk In Communities (ARIC) Study

BACKGROUND AND PURPOSE

Premature ventricular complexes (PVCs) on a 2-minute electrocardiogram are a common, largely asymptomatic finding associated with increased risk of coronary heart disease and death. They may reflect atherosclerosis or other pathogenic pathways that predispose to arrhythmias and stroke.

METHODS

We conducted a prospective evaluation of the Atherosclerosis Risk In Communities Study cohort (n=14,783) of middle-aged men and women to assess whether the presence of PVCs at study baseline (1987 to 1989) influenced the risk of incident stroke through December 31, 2004.

RESULTS

PVCs were seen in 6.1% of the participants at baseline, and 729 (4.9%) had incident stroke. The unadjusted cumulative proportion of incident stroke in individuals with any PVC was 6.6% compared with 4.1% in those without PVC. The unadjusted hazard ratio of incident stroke in individuals with any PVC compared with those without any PVCs was 1.71 (95% CI, 1.33 to 2.20). Among individuals without hypertension and diabetes at baseline, PVCs were independently associated with incident stroke (hazard ratio: 1.72; 95% CI: 1.14 to 2.59). Among those with either diabetes or hypertension, the presence of any PVCs did not increase the risk of stroke. The association was stronger for noncarotid embolic stroke than for thrombotic stroke and its magnitude increased with higher frequency of PVCs.

CONCLUSIONS

Frequent PVCs are associated with risk of incident stroke in participants free of hypertension and diabetes. This suggests that PVCs may contribute to atrioventricular remodeling or may be a risk marker for incident stroke, particularly embolic stroke.

Mechanisms of ventricular fibrillation initiation in MADIT II patients with implantable cardioverter defibrillators

BACKGROUND

The availability of stored intracardiac electrograms from implantable defibrillators (ICDs) has facilitated the study of the mechanisms of ventricular tachyarrhythmia onset. This study aimed to determine the patterns of initiation of ventricular fibrillation (VF) in Multicenter Automatic Defibrillator Implantation Trial (MADIT) II patients along with associated electrocardiogram (ECG) parameters and clinical characteristics.

METHODS

Examination of stored electrograms enabled us to evaluate the rhythm preceding each episode of VF and to calculate (intracardiac) ECG parameters including QT, QT peak (QTp), coupling interval, and prematurity index.

RESULTS

Sixty episodes of VF among 29 patients (mean age 64.4 +/- 2.5 years) were identified. A single ventricular premature complex (VPC) initiated 46 (77%) episodes whereas a short-long-short (SLS) sequence accounted for 14 (23%) episodes. Of the 29 patients studied, 23 patients had VF episodes preceded by a VPC only, two patients with SLS only, and four patients with both VPC and SLS-initiated episodes. There were no significant differences between initiation patterns in regards to the measured ECG parameters; a faster heart rate with SLS initiation (mean RR prior to VF of 655 +/- 104 ms for SLS and 744 +/- 222 ms for VPC) approached significance (P = 0.06). The two patients with SLS only were not on beta-blockers compared to 83% of the VPC patients.

CONCLUSION

Ventricular fibrillation is more commonly initiated by a VPC than by a SLS sequence among the MADIT II population. Current pacing modes designed to prevent bradycardia and pause-dependent arrhythmias are unlikely to decrease the incidence of VPC-initiated episodes of VF.

Effects of a rate smoothing algorithm for prevention of ventricular arrhythmias: Results of the Ventricular Arrhythmia Suppression Trial (VAST)

BACKGROUND

Rate smoothing, which is available in some pacemakers and implantable cardioverter defibrillators (ICDs), has been used to prevent Torsades de Pointes in patients with long QT syndrome. Its efficacy in general ventricular arrhythmia prevention has not been determined.

OBJECTIVES

The purpose of the Ventricular Arrhythmia Suppression Trial (VAST) was to prospectively investigate whether rate smoothing could significantly reduce the incidence of ventricular tachyarrhythmias in a large, broad population of patients with ICDs.

METHODS

Five hundred sixty-nine patients were enrolled at 57 participating centers and implanted with a commercially available Guidant ICD. A single-blinded crossover design was used in which each patient was randomized at implant to one of two treatment sequences: either rate smoothing on (RS On) followed by rate smoothing off (RS Off), or RS Off followed by RS On. This mode sequence was randomly determined and assigned in a 1:1 fashion using randomized permuted blocks by site. Each mode was followed for 6 months. Programming of rate smoothing was prescribed as 12% Down and 12% Up for the duration of the RS On period.

RESULTS

Of enrolled patients, 281 were randomized to RS Off followed by RS On, and 288 to RS On followed by RS Off. With RS On, 75 (23%) patients experienced a reduction in arrhythmias, 76 (23%) saw an increase in arrhythmias, and the remaining 176 (54%) had no difference. No significant difference (P = .58) in frequency of arrhythmias with RS On vs RS Off was found.

CONCLUSION

Rate smoothing does not result in a reduction in ventricular arrhythmias in a heterogeneous population of patients receiving ICDs.

Initiation of monomorphic ventricular tachycardia: electrophysiological, clinical features, and drug therapy in patients with implantable defibrillators

At least 2 distinct patterns of sustained monomorphic ventricular tachycardia (MVT) have been ascribed during analysis of stored intracardiac electrograms retrieved from implantable cardioverter defibrillators and Holter recordings in patients with ventricular arrhythmia. We aimed to investigate the electrophysiological features of MVT with different initiation patterns in patients with implantable cardioverter defibrillators and to assess whether there is a relationship of the initiation patterns of sustained MVT with clinical characteristics and efficacy of antiarrhythmic therapy. Seventy-four stored intracardiac electrograms in 21 patients (mean age of 68.2 +/- 4.2 years) with MVT were evaluated. Cardiovascular diagnosis included coronary artery disease in 85.7% of the patients. All MVT episodes were classified as those initiating with ventricular premature beats (nonsudden onset MVT) and those without ventricular ectopy preceding tachycardia (sudden onset MVT). There was significant difference in left ventricular ejection fraction between MVTs with different initiation pattern, being the lower in those with nonsudden onset (33.6% +/- 38.4% vs. 38.4 +/- 7.0%, P <.04). Ventricular tachycardia cycle length was shorter in group of MVT with nonsudden onset as compared with sudden onset (338.5% +/- 48.1% vs. 376.8% +/- 57.0%, P <.02). Tachycardia with sudden onset was associated with shorter preceding RR interval than tachycardia with nonsudden onset (821.8 +/- 136.2% vs. 748.7 +/- 107.7%, P <.01). There were no significant differences in the type of antiarrhythmic drug therapy used between groups (P >.05). Monomorphic ventricular tachycardias with nonsudden onset occurred more frequently than with sudden onset, without precipitating RR cycles shortening, are faster in rate, associating with lower ejection fraction. Monomorphic ventricular tachycardias with sudden onset are characterized by preceding shortening of RR intervals, slower cycle length, and less worsening of ejection fraction.

Study of precursors of ventricular tachycardia from data stored in the memory of a dual chamber implantable cardioverter defibrillator

This study was performed to examine precursors of ventricular tachyarrhythmias in patients who experienced a sustained ventricular tachyarrhythmia and received appropriate therapy by ICD. From an overall consecutive population of 77 patients, 18 patients (1 woman, mean age 61.7 +/- 10.8 years) were selected for having experienced a sustained ventricular tachyarrhythmia and received at least one appropriate ICD therapy preceded by 20 minutes of internal information. The number of premature ventricular complexes (PVCs)/min for each of the 20 minutes preceding the onset of ventricular tachyarrhythmia, the shortest coupling intervals between PVC and normal sinus beat, and the presence of short-long-short (SLS) interval sequences were examined. Data were stratified according to underlying disease, left ventricular ejection fraction, rate of ventricular tachyarrhythmia, and antiarrhythmic therapy. One hundred twenty-eight episodes of spontaneous ventricular tachyarrhythmia were retrieved. Rapid ventricular tachyarrhythmia (>160 beats/min) were preceded by a significantly greater mean number (3.71 +/- 6.36)of PVCs than slower ventricular tachyarrhythmia (<or=160 beats/min) (0.63 +/- 0.88, P = 0.0004). The mean shortest PVC coupling interval was significantly shorter in patients with (588 +/- 99 ms) versus without (643 +/- 111 ms, P = 0.03)ischemic heart disease, before episodes of rapid(527 +/- 55 ms)versus slower (636 +/- 105 ms, P = 0.0001)ventricular tachyarrhythmia, and in the absence (538 +/- 80 ms)versus the presence(620 +/- 105 ms, P = 0.006)of amiodarone. SLS sequences preceded 29% of rapid ventricular tachyarrhythmic episodes, versus 8% of the slower ventricular tachyarrhythmia (P < 0.01). Significant differences were found in the characteristics of PVCs preceding ventricular tachyarrhythmic episodes in accordance to their rate and the underlying cardiomyopathy. Though insufficient in isolation, these findings may be helpful when combined with other observations to develop preventive algorithms, or to refine the programming of implantable devices.

Analysis of the corrected QT before the onset of nonsustained ventricular tachycardia in patients with hypertrophic cardiomyopathy

This study examined ventricular repolarization before the onset of 37 episodes of nonsustained ventricular tachycardia (NSVT) in 26 untreated patients with hypertrophic cardiomyopathy (HCM). Fourteen episodes were recorded in patients with a history of cardiac arrest or patients who died suddenly during follow-up. The QT interval was measured beat-by-beat on 24-hour ambulatory electrocardiograms. Mean 24-hour, hourly QTc and QTc of the last 10 beats prior to NSVT, consisted of 4-50 cycles (mean 9 +/- 10), at the fastest rates of 100-175 beats/min (mean 122 +/- 22) were analyzed. NSVT was more prevalent during nighttime (23 episodes), than during daytime (14 episodes, P < 0.05). No significant differences were observed between mean 24-hour, mean hourly QTc during the hour with NSVT, and QTc of the last 10 cycles prior to onset of NSVT. QTc was significantly longer in patients with a history of sudden cardiac death (SCD) or who died suddenly during follow-up than in survivors. The 24-hour QT variability was higher in nonsurvivors than in survivors (-39 +/- 6 vs 33 +/- 6 ms, P = 0.03). Episodes of NSVT in untreated patients with hypertrophic cardiomyopathy were more frequent during the nighttime. The 24-hour QT variability was higher in nonsurvivors than in survivors.

Heart rate variability before the onset of ventricular tachycardia: differences between slow and fast arrhythmias

BACKGROUND

We tested whether or not heart rate variability (HRV) changes can serve as early signs of ventricular tachycardia (VT) and predict slow and fast VT in patients with an implantable cardioverter defibrillator (ICD).

METHODS AND RESULTS

We studied the ICD stored 1000 beat-to-beat intervals before the onset of VT (131 episodes) and during a control time without VT (74 series) in 63 chronic heart failure ICD patients. Standard HRV parameters as well as two nonlinear parameters, namely 'Polvar10' from symbolic dynamics and the finite time growth rates 'Fitgra9' were calculated. Comparing the control and the VT series, no linear HRV parameter showed a significant difference. The nonlinear parameters detected a significant increase in short phases with low variability before the onset of VT (for time series with less than 10% ectopy, P<0.05). Subdividing VT into fast (cycle length <or=270 ms) and slow (>270 ms) events, we found that the onset of slow VT was characterized by a significant increase in heart rate, whereas fast VT was triggered during decreased heart rates, compared to the control series.

CONCLUSIONS

Our data may permit the development of automatic ICD algorithms based on nonlinear dynamic HRV parameters to predict VT before it starts. Furthermore, they may facilitate improved prevention strategies.

Pause-dependent polymorphic ventricular tachycardia during long-term treatment with dofetilide: a placebo-controlled, implantable cardioverter-defibrillator-based evaluation

OBJECTIVES

To compare the incidence of pause-dependent polymorphic ventricular tachycardia (PVT) in patients with implantable cardioverter-defibrillators (ICDs) randomly assigned to the QT-prolonging antiarrhythmic dofetilide or placebo.

BACKGROUND

Drug-related torsade de pointes (TdP) is usually recognized within days of initiating therapy, but its incidence during long-term therapy is unknown.

METHODS

We assessed the frequency of TdP and ICD electrograms compatible with TdP in a multicenter study that randomized ICD patients to placebo (n = 87) or dofetilide (n = 87). As reported elsewhere, the number of patients with a primary trial end point (ICD intervention for VT or ventricular fibrillation) was similar in the two groups. For this analysis, a qualifying event was TdP (on electrocardiogram) or an intracardiac electrogram showing pause-dependent PVT.

RESULTS

A total of 620 electrograms obtained in 131 patients were analyzed blindly by prospectively defined criteria for episodes of pause-dependent polymorphic VT. These were identified in 15/87 (17%) patients receiving dofetilide and 5/87 (6%) patients on placebo (p < 0.05). Five of these episodes were early (<3 days), all of which were TdP on dofetilide. There were 15 late events, 10 on dofetilide and five on placebo (p = 0.29). The median time to a late event was 22 days (range 6 to 107 days) for dofetilide and 99 days (range 34 to 207 days) for placebo.

CONCLUSIONS

Pause-dependent PVT was more common among patients receiving dofetilide, although total VT incidence was similar in the two groups. These data suggest that in ICD patients either long-term dofetilide therapy is associated with an increased risk of TdP or the drug alters VT morphology.

Circadian variation and onset mechanisms of ventricular tachyarrhythmias in patients with coronary disease versus idiopathic dilated cardiomyopathy

To determine the circadian variations and the onset mechanisms of ventricular tachyarrhythmias (VT) in patients with implantable cardioverter defibrillators, stored electrograms of 364 VT episodes occurring in 40 patients with coronary artery disease (CAD) and in 29 patients with idiopathic dilated cardiomyopathy (DCM) were analyzed. A similar circadian distribution of VT episodes was observed in both groups, with a morning peak and less pronounced evening peak. After exclusion of patients with atrial fibrillation, VT onset was classified as (1) sudden if preceded by > or = 8 regular cycles without ventricular premature beats, (2) onset with a short-long-short interval, and (3) a more complex onset with variable patterns of ventricular premature beats before initiation of VT. Sudden onset was found in 26% and 21% of VTs in CAD and DCM respectively. A short-long-short interval preceded 29% of VTs in CAD compared to 14% of VTs in DCM (P < 0.05). A more complex onset was observed in the remaining 45% of VTs in CAD and 65% of VTs in DCM (P < 0.05). In conclusion, patients with DCM and CAD had similar circadian distributions of VT episodes. The majority of episodes were preceded by complex occurrence of ventricular premature beats rather than by the classic short-long-short sequence. These findings have important implications for the development of preventive pacing methods.

Analysis of intracardiac electrograms showing monomorphic ventricular tachycardia in patients with implantable cardioverter-defibrillators

Ventricular tachycardia (VT) initiation and its relation to various clinical factors was studied by reviewing intracardiac electrograms from patients with implantable cardioverter-defibrillators. Events were divided into (1) sudden onset without preceding ventricular premature complexes (VPCs), (2) extrasystolic onset with VPCs, or (3) paced, depending on the type and morphology of the last 5 beats before initiation of VT. Prematurity index, sinus rate, cycle length, and presence of short-long-short sequence for each episode was noted. A total of 268 episodes of VT among 52 patients were analyzed. Extrasystolic initiation was the most frequent pattern (177; 66%) followed by sudden onset (75; 28%) and paced (16; 6%). Among extrasystolic onset, 99 episodes (56%) were due to multiple VPCs and 149 episodes (84%) had different VPC morphology than the subsequent VT. Among pacing-induced VT, 13 of 16 episodes were due to inappropriate pacing due to undersensing of prior R waves. Sudden-onset episodes were slower (mean cycle length 383+/-97 ms) than extrasystolic (mean cycle length 336+/-88 ms, p = 0.002) and paced (mean cycle length 313+/-85 ms, p = 0.01) onset. Patients in the sudden-onset group had better left ventricular ejection fraction (33+/-15%) than the extrasystolic (29+/-11%, p<0.001) and paced (28+/-14%, p<0.01) groups. Extrasystolic onset with multiple, late coupled VPCs was the most common pattern of VT initiation and was associated with lower ejection fraction. Sudden-onset initiation was more common with better preserved systolic function.

Short-term forecasting of life-threatening cardiac arrhythmias based on symbolic dynamics and finite-time growth rates

Ventricular tachycardia or fibrillation (VT-VF) as fatal cardiac arrhythmias are the main factors triggering sudden cardiac death. The objective of this study is to find early signs of sustained VT-VF in patients with an implanted cardioverter-defibrillator (ICD). These devices are able to safeguard patients by returning their hearts to a normal rhythm via strong defibrillatory shocks; additionally, they store the 1000 beat-to-beat intervals immediately before the onset of a life-threatening arrhythmia. We study these 1000 beat-to-beat intervals of 17 chronic heart failure ICD patients before the onset of a life-threatening arrhythmia and at a control time, i.e., without a VT-VF event. To characterize these rather short data sets, we calculate heart rate variability parameters from the time and frequency domain, from symbolic dynamics as well as the finite-time growth rates. We find that neither the time nor the frequency domain parameters show significant differences between the VT-VF and the control time series. However, two parameters from symbolic dynamics as well as the finite-time growth rates discriminate significantly both groups. These findings could be of importance in algorithms for next generation ICD's to improve the diagnostics and therapy of VT-VF.

Comparison of therapy detection times between implantable cardioverter defibrillators with standard dual- and single-chamber pacing

Previous implantable cardioverter defibrillators (ICDs) required patients in need of dual-chamber (DDD) pacing for improved hemodynamic status to undergo implantation of separate devices to treat bradycardia and/or ventricular arrhythmias. An investigation was conducted to verify the performance of a new ICD that combines both therapies.Sixty-nine patients at 17 European and Canadian centers were implanted with VENTAK AV models 1810/1815, ICD's that includes DDD pacing and algorithms designed to differentiate between atrial and ventricular arrhythmias. 36 of the cohort were compared to 32 patients tested at six centers with an external test device (VENTAK MINI). In both cohorts detection times were calculated for ventricular fibrillation (VF) induced at implant. The mean detection times (DT) from the VENTAK AV device were compared to the DT from the VENTAK MINI device. Patient characteristics of the VENTAK AV and the VENTAK MINI control groups were similar. Mean VF detection time (+/-SD) with the VENTAK AV device was 2.21 +/- 0.54 seconds, as compared with 1.87 +/- 0.62 seconds with the VENTAK MINI (p < 0.01), indicating that the difference in means did not exceed one second. The VENTAK AV system function did not demonstrate interaction with the pacemaker function, as indicated by the clinical significance with the detection times of the study device. The difference in detection times between cohorts did not statistically exceed one second. Appropriate detection of the new ICD was not compromised by the addition of the dual-chamber pacing therapy.

Algorithm for the prevention of ventricular tachycardia onset: the Prevent Study

The Prevent Study is designed to investigate the effect of a rate-smoothing algorithm on the onset of ventricular tachycardia in patients with implanted cardioverter defibrillators (ICD) with dual-chamber pacing and sensing function. Included in the study are patients who require ICD therapy for recurrent ventricular tachycardia or aborted cardiac arrest. After giving informed consent to the study, the patients receive a Ventak AV ICD (CPI-Guidant, St. Paul, MN). The patients are randomized to start either with active or inactive rate-smoothing algorithm. After 3 months, all patients cross over to the opposite group. Questionnaires are used to investigate quality-of-life issues. A total of 240 patients will be enrolled in the study, with a minimum follow-up of 6 months.

QT interval and arrhythmic risk assessment after myocardial infarction

To assess ventricular repolarization features as predictors of ventricular tachyarrhythmias (VT) in patients with previous myocardial infarction, we performed a dynamic study of QT interval from 24-hour electrocardiographic data. QT rate dependence was enhanced in patients with VT when compared with patients without VT.