Activated human platelet products induce proarrhythmic effects in ventricular myocytes

Acetylsalicylic acid use is associated with reduced risk of out-of-hospital cardiac arrest in the general population: Real-world data from a population-based study

Aim

Activated blood platelet products facilitate myocardial intracellular Ca2+ overload, thereby provoking afterdepolarizations and increasing susceptibility of ischemic myocardium to ventricular fibrillation (VF). These effects are counteracted in vitro by acetylsalicylic acid (ASA), but no prior study investigated whether ASA is associated with decreased out-of-hospital cardiac arrest (OHCA) risk on a population level. Therefore, we studied whether ASA and other antiplatelet drugs (carbasalate calcium, clopidogrel) are associated with decreased risk of OHCA.

Methods

We conducted a population-based case-control study among individuals (772 OHCA-cases with documented VT/VF, 2444 non-OHCA-controls) who had used antiplatelet drugs in the year before index-date (OHCA-date), and studied the association between current antiplatelet drug use and OHCA-risk with multivariable logistic regression analysis.

Results

ASA use was associated with reduced OHCA-risk (adjusted odds ratio (ORadj) 0.6 [0.5–0.8]), and more so in women (ORadj 0.3 [0.2–0.6]) than in men (ORadj 0.7 [0.5–0.95], Pinteraction 0.021). Carbasalate calcium was associated with decreased OHCA-risk in women (ORadj 0.5 [0.3–0.9]), but not in men (ORadj 1.3 [0.96–1.7], Pinteraction 0.005). Clopidogrel was not associated with reduction in OHCA-risk. Risk reduction associated with ASA in patients with OHCA was similar in the presence of acute myocardial infarction (AMI) (ORadj 0.6 [0.4–0.9]) and in the absence of AMI (ORadj 0.7 [0.4–1.2]).

Conclusion

ASA use was associated with reduced OHCA-risk in both sexes, and more so in women, while carbasalate calcium only protected women. Clopidogrel was not associated with reduced OHCA-risk.

Neurokinin-3 receptor activation selectively prolongs atrial refractoriness by inhibition of a background K+ channel

The cardiac autonomic nervous system (ANS) controls normal atrial electrical function. The cardiac ANS produces various neuropeptides, among which the neurokinins, whose actions on atrial electrophysiology are largely unknown. We here demonstrate that the neurokinin substance-P (Sub-P) activates a neurokinin-3 receptor (NK-3R) in rabbit, prolonging action potential (AP) duration through inhibition of a background potassium current. In contrast, ventricular AP duration was unaffected by NK-3R activation. NK-3R stimulation lengthened atrial repolarization in intact rabbit hearts and consequently suppressed arrhythmia duration and occurrence in a rabbit isolated heart model of atrial fibrillation (AF). In human atrial appendages, the phenomenon of NK-3R mediated lengthening of atrial repolarization was also observed. Our findings thus uncover a pathway to selectively modulate atrial AP duration by activation of a hitherto unidentified neurokinin-3 receptor in the membrane of atrial myocytes. NK-3R stimulation may therefore represent an anti-arrhythmic concept to suppress re-entry-based atrial tachyarrhythmias, including AF.

The cardiac autonomic nervous system produces various neuropeptides, such as neurokinin substance-P (Sub-P), whose function remains largely unclear. Here, authors show that Sub-P causes a receptor-mediated prolongation of the atrial action potential through a reduced background potassium current, and prevents atrial fibrillation.

Altered platelet contents in survivors of early ischemic ventricular fibrillation: preliminary findings

Early ischemic ventricular fibrillation (VF) in the setting of an acute myocardial infarction (AMI) due to thrombotic coronary occlusion remains a major health problem. Several animal studies have shown that platelet-dense granule contents released during thrombus formation can induce arrhythmias. We hypothesize that the platelet release reaction is involved in the predisposition to early ischemic VF. A case-control study was performed in patients who survived VF during a first AMI ("cases," n = 26) and in patients with one previous AMI without arrhythmias ("controls," n = 24). All patients were on aspirin 100 mg OD. Baseline platelet activation was assessed with flow cytometry. Response to activation was assessed with aggregometry, flow cytometry and PFA-100 analysis. Differences in platelet contents and content release were assessed by labeling platelet-dense granules with mepacrine and by measuring serotonin and ADP/ATP content. Patient and infarct characteristics and baseline platelet function tests were similar between groups. The mean time from event was 4.9 (±3.2) years among cases and 4.7 (±2.7) years among controls. Dense granule release was similar in cases versus controls. Platelet serotonin content in cases was higher than in controls (611 ± 118 ng/10E(9) platelets vs. 536 ± 141 ng/10(9), p = 0.048). Even years after the event, elevations in the platelet dense granule contents between VF survivors and controls may be detected. These preliminary findings shed new light on the pathophysiological mechanisms underlying ischemic VF, as platelet-dense granules may contain mediators of early ischemic VF risk.

Lysophosphatidic acid increases the electrophysiological instability of adult rabbit ventricular myocardium by augmenting L-type calcium current

Lysophosphatidic acid (LPA) has diverse actions on the cardiovascular system and is widely reported to modulate multiple ion currents in some cell types. However, little is known about its electrophysiological effects on cardiac myocytes. This study investigated whether LPA has electrophysiological effects on isolated rabbit myocardial preparations. The results indicate that LPA prolongs action potential duration at 90% repolarization (APD₉₀) in a concentration- and frequency-dependent manner in isolated rabbit ventricular myocytes. The application of extracellular LPA significantly increases the coefficient of APD₉₀ variability. LPA increased L-type calcium current (I_Ca,L) density without altering its activation or deactivation properties. In contrast, LPA has no effect on two other ventricular repolarizing currents, the transient outward potassium current (I_to) and the delayed rectifier potassium current (I_K). In arterially perfused rabbit left ventricular wedge preparations, the monophasic action potential duration, QT interval, and Tpeak-end are prolonged by LPA. LPA treatment also significantly increases the incidence of ventricular tachycardia induced by S₁S₂ stimulation. Notably, the effects of LPA on action potentials and I_Ca,L are PTX-sensitive, suggesting LPA action requires a G_i-type G protein. In conclusion, LPA prolongs APD and increases electrophysiological instability in isolated rabbit myocardial preparations by increasing I_Ca,L in a G_i protein-dependent manner.