Irregular Ventricular Activation Results in QT Prolongation and Increased QT Dispersion: A New Insight Into the Mechanism of AF-Induced Ventricular Arrhythmogenesis

Association of a simple SACAF score with bystander witnessed sudden death due to ventricular tachyarrhythmias in a multicenter cohort

Out-of-hospital cardiac arrest (OHCA) remains a major threat to public health worldwide. OHCA patients presenting initial shockable ventricular tachycardia/ventricular fibrillation (VT/VF) rhythm have a better survival rate. We sought to develop a simple SACAF score to discriminate VT/VF from non-VT/VF OHCAs based on the Taiwan multicenter hospital-based registry database. We analyzed the in- and pre-hospital data, including demographics, baseline comorbidities, response times, automated external defibrillator information, and the 12-lead ECG recording closest to the OHCA event in bystander-witnessed OHCA patients. Among the 461 study patients, male sex (OR 2.54, 95% CI = 1.32–4.88, P = 0.005), age ≤ 65 years (OR 2.78, 95% CI = 1.64–4.70, P < 0.001), cardiovascular diseases (OR 2.97, 95% CI = 1.73–5.11, P < 0.001), and atrial fibrillation (AF) (OR 2.36, 95% CI = 1.17–4.76, P = 0.017) were independent risk factors for VT/VF OHCA (n = 81) compared with non-VT/VF OHCA (n = 380). A composite SACAF score was developed (male Sex, Age ≤ 65 years, Cardiovascular diseases, and AF) and compared with the performance of a modified CHA₂DS₂-VASc score (Cardiovascular diseases, Hypertension, Age ≥ 75 years, Diabetes, previous Stroke, Vascular disease, Age 65–74 years, female Sex category). The area under the receiver operating characteristic curve (AUC) of the SACAF was 0.739 (95% CI = 0.681–0.797, P < 0.001), whereas the AUC of the modified CHA₂DS₂-VASc was 0.474 (95% CI = 0.408–0.541, P = 0.464). A SACAF score of ≥ 2 was useful in discriminating VT/VF from non-VT/VF OHCAs with a sensitivity of 0.75 and a specificity of 0.60. In conclusion, the simple SACAF score appears to be useful in discriminating VT/VF from non-VT/VF bystander-witnessed OHCAs and the findings may also shed light on future mechanistic evaluation.

Atrial fibrillation increases the risk of recurrent ventricular tachyarrhythmias in implantable cardioverter defibrillator recipients

BACKGROUND

Data regarding recurrences of ventricular tachyarrhythmias in implantable cardioverter defibrillator (ICD) recipients according to atrial fibrillation is limited.

OBJECTIVE

To assess the prognostic impact of atrial fibrillation on recurrences of ventricular tachyarrhythmias in implantable cardioverter defibrillator recipients.

METHODS

A large retrospective registry was used, including all ICD recipients with episodes of ventricular tachycardia or fibrillation from 2002 to 2016. Patients with atrial fibrillation were compared to those without atrial fibrillation. The primary endpoint was first recurrence of ventricular tachyarrhythmias at 5 years. Secondary endpoints comprised recurrences of ICD-related therapies, first cardiac rehospitalization and all-cause mortality at 5 years. Cox regression, Kaplan-Meier and propensity score-matching analyses were applied.

RESULTS

A total of 592 consecutive ICD recipients were included (33% with atrial fibrillation). Atrial fibrillation was associated with reduced freedom from recurrent ventricular tachyarrhythmias (42% vs. 50%, log-rank P=0.004; hazard ratio 1.445, 95% confidence interval 1.124-1.858), mainly attributable to recurrent ventricular fibrillation in secondary-preventive ICD recipients. Accordingly, atrial fibrillation was associated with reduced freedom from first appropriate ICD therapies (31% vs. 42%, log-rank P=0.001; hazard ratio 1.598, 95% confidence interval 1.206-2.118). Notably, the primary endpoint of freedom from first episode of recurrent ventricular tachyarrhythmias was still reduced in those with atrial fibrillation compared to those without atrial fibrillation after propensity score matching. Regarding secondary endpoints, patients with atrial fibrillation still showed a trend towards reduced freedom from appropriate ICD therapies.

CONCLUSIONS

Atrial fibrillation was associated with increased rates of recurrent ventricular tachyarrhythmias and appropriate device therapies in ICD recipients with ventricular tachyarrhythmias.

Prolonged Exposure to Microgravity Reduces Cardiac Contractility and Initiates Remodeling in Drosophila

Understanding the effects of microgravity on human organs is crucial to exploration of low-earth orbit, the moon, and beyond. Drosophila can be sent to space in large numbers to examine the effects of microgravity on heart structure and function, which is fundamentally conserved from flies to humans. Flies reared in microgravity exhibit cardiac constriction with myofibrillar remodeling and diminished output. RNA sequencing (RNA-seq) in isolated hearts revealed reduced expression of sarcomeric/extracellular matrix (ECM) genes and dramatically increased proteasomal gene expression, consistent with the observed compromised, smaller hearts and suggesting abnormal proteostasis. This was examined further on a second flight in which we found dramatically elevated proteasome aggregates co-localizing with increased amyloid and polyQ deposits. Remarkably, in long-QT causing sei/hERG mutants, proteasomal gene expression at 1g, although less than the wild-type expression, was nevertheless increased in microgravity. Therefore, cardiac remodeling and proteostatic stress may be a fundamental response of heart muscle to microgravity.

Atrial Fibrillation Is Associated with Increased Mortality in Patients Presenting with Ventricular Tachyarrhythmias

Heterogenous data about the prognostic impact of atrial fibrillation (AF) in patients with ventricular tachyarrhythmias exist. Therefore, this study evaluates this impact of AF in patients presenting with ventricular tachyarrhythmias. 1,993 consecutive patients presenting with ventricular tachyarrhythmias (i.e. ventricular tachycardia and fibrillation (VT, VF)) on admission at one institution were included (from 2002 until 2016). All medical data of index and follow-up hospitalizations were collected during the complete follow-up period for each patient. Statistics comprised univariable Kaplan-Meier and multivariable Cox regression analyses in the unmatched consecutive cohort and after propensity-score matching for harmonization. The primary prognostic endpoint was long-term all-cause mortality at 2.5 years. AF was present in 31% of patients presenting with index ventricular tachyarrhythmias on admission (70% paroxysmal, 9% persistent, 21% permanent). VT was more common (67% versus 59%; p = 0.001) than VF (33% versus 41%; p = 0.001) in AF compared to non-AF patients. Long-term all-cause mortality at 2.5 years occurred more often in AF compared to non-AF patients (mortality rates 40% versus 24%, log rank p = 0.001; HR = 1.825; 95% CI 1.548-2.153; p = 0.001), which may be attributed to higher rates of all-cause mortality at 30 days, in-hospital mortality and mortality after discharge (p < 0.05) (secondary endpoints). Mortality differences were observed irrespective of index ventricular tachyarrhythmia (VT or VF), LV dysfunction or presence of an ICD. In conclusion, this study identifies AF as an independent predictor of death in patients presenting consecutively with ventricular tachyarrhythmias.

Prognostic Impact of Atrial Fibrillation in Electrical Storm

BACKGROUND

Data regarding the prognostic impact of atrial fibrillation (AF) in patients with electrical storm (ES) is rare.

OBJECTIVES

This study sought to assess the prognostic impact of AF in patients with ES on mortality, rehospitalization, major adverse cardiovascular events (MACE) and recurrence of ES (ES-R).

METHODS

All consecutive implantable cardioverter defibrillator (ICD) patients presenting with ES were included retrospectively from 2002 to 2016. Patients with AF were compared to non-AF patients. The primary prognostic endpoint was all-cause mortality. Secondary endpoints were in-hospital mortality, rehospitalization rates, MACE and ES-R.

RESULTS

A total of 87 ES patients with ICD were included and followed up to 2.5 years; 43% suffered from AF. The presence of AF was associated with increased all-cause mortality (47 vs. 29%, log-rank p = 0.052; hazard ratio [HR] 1.969, 95% confidence interval [CI] 0.981-3.952, p = 0.057), which was no longer present after multivariable adjustment for age, diabetes and dilated cardiomyopathy. Furthermore, AF was associated with increased rates of overall rehospitalization (61 vs. 31%, log-rank p = 0.013; HR 2.381, 95% CI 1.247-4.547, p = 0.009), especially due to AF (14 vs. 0%, p = 0.001) and acute heart failure (AHF) (28 vs. 10%, p = 0.018; HR 3.754, 95% CI 1.277-11.038, p = 0.016). Notably, AF was not associated with differences in MACE (55 vs. 37%, log rank p = 0.339) and ES-R (28 vs. 25%, log rank p = 0.704).

CONCLUSION

In ES patients, presence of AF was univariably associated with increased rates of all-cause mortality at 2.5 years. Furthermore, AF was multivariably associated with overall rehospitalization, especially due to AF and AHF.

Early cardiac electrographic and molecular remodeling in a model of status epilepticus and acquired epilepsy

OBJECTIVES

A myriad of acute and chronic cardiac alterations are associated with status epilepticus (SE) including increased sympathetic tone, rhythm and ventricular repolarization disturbances. Despite these observations, the molecular processes underlying SE-associated myocardial remodeling remain to be identified. Here we determined early SE-associated myocardial electrical and molecular alterations using a model of SE and acquired epilepsy.

METHODS

We performed electrocardiography (ECG) assessments in rats beginning at 2 weeks following kainate-induced SE, and calculated short-term variability (STV) of the corrected QT intervals (QTc) as a marker of ventricular stability. Using western blotting, we quantified myocardial β1-adrenergic receptors (β1-AR) and ventricular gap junction protein connexin 43 (Cx43) levels as makers of increased sympathetic tone. We determined the activation status of three kinases associated with sympathetic stimulation and their downstream ion channel targets: extracellular signal-regulated kinase (ERK), protein kinase A (PKA), Ca²⁺ /calmodulin-dependent protein kinase II (CamKII), hyperpolarization-activated cyclic nucleotide-gated channel subunit 2 (HCN2), and voltage-gated potassium channels 4.2 (Kv_4.2 ). We investigated whether SE was associated with altered Ca²⁺ homeostasis by determining select Ca²⁺ -handling protein levels using western blotting.

RESULTS

Compared with the sham group, SE animals exhibited higher heart rate, longer QTc interval, and higher STV beginning at 2 weeks following SE. Concurrently, the myocardium of SE rats showed lower β1-AR and higher Cx43 protein levels, higher levels of phosphorylated ERK, PKA, and CamKII along with decreased HCN2 and Kv_4.2 channel levels. In addition, the SE rats had altered proteins levels of Ca²⁺ -handling proteins, with decreased Na⁺ /Ca²⁺ exchanger-1 and increased calreticulin.

SIGNIFICANCE

SE triggers early molecular alterations in the myocardium consistent with increased sympathetic tone and altered Ca²⁺ homeostasis. These changes, coupled with early and persistent ECG abnormalities, suggest that the observed molecular alterations may contribute to SE-associated cardiac remodeling. Additional mechanistic studies are needed to determine potential causal roles.