DIagnostics, Fatty Acids and Vitamin D in SCA
DIagnostics, Fatty Acids and Vitamin D in SCA
Sudden cardiac death (SCD) is a major cause of mortality in industrialized countries and
 represents a major health issue. The survival rate after out-of-hospital cardiac arrest
 (OHCA) is only 10-15%, regardless of first recorded rhythm. Prior heart disease is a major
 risk factor for sudden cardiac arrest (SCA), and coronary artery disease (CAD) is the most
 common underlying cause. A better understanding of pathophysiological mechanisms occurring
 during cardiac arrest (CA), earlier diagnosis of underlying cause as well as identification
 of risk factors related to CA may improve patient treatment and increase survival. In our
 out-of-hospital cardiac arrest (OHCA)-study, we intend to investigate whether biomarkers,
 such as copeptin, hs-cTnT and NT-proBNP in addition to clinical evaluation may improve risk
 stratification and supply information related to pathophysiology.

 Furthermore, we intend to gather additional pathophysiological information related to
 coagulation activation in CA and cardiopulmonary resuscitation (CPR), as intravascular
 thrombosis may impair microcirculation and reduce end-organ blood flow which is associated
 with a poor prognosis. We intend to study coagulation activation during and immediately after
 SCA with regard to outcome, and assess the contribution of the intrinsic system, measured
 together with that of the extrinsic system.

 Low levels of n-3 fatty acids (FA) are reported as a risk factor for SCD. Red blood cell
 eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) may serve as a useful surrogate of
 cardiac omega-3 fatty acid status. The exact mechanism by which FAs might protect against
 serious cardiac arrhythmias is not known, but they are expected to exert a membrane
 stabilizing effect during an ischemic episode. In our study we intend to evaluate the
 association between ventricular fibrillation (VF) and the content of EPA and DHA in red blood
 cells. Furthermore, as vitamin D is associated with n-3 FAs in the diet, we also aim at
 investigating the association between 25-hydroxy (OH)-vitamin D and VF.
Background:

 Sudden cardiac death (SCD), also termed sudden cardiac arrest (SCA), accounts for
 approximately 15 percent of the total mortality in industrialized countries. In Europe, the
 incidence of out-of-hospital Emergency Medical Services (EMS) attended sudden cardiac arrest
 (SCA) is estimated to 81.6/100 000 person-years, 52.5 % of which is presumed to have a
 cardiac cause [1]. Coronary artery disease (CAD) is the most common underlying heart disease
 associated with out-of-hospital cardiac arrest (OHCA) [2]. SCD is the initial presentation of
 CAD in 15 percent of CAD-patients [3]. Furthermore, it is also the most frequent mechanism of
 death in patients with known CAD, accounting for 40-50 percent of CAD-mortality [4]. Compared
 to healthy subjects the incidence of SCD is six- to tenfold higher in the presence of
 clinically recognized heart disease [5], and cardiomyopathies represents the second largest
 cause of SCD [6]. Despite early advanced cardiopulmonary resuscitation (CPR) provided by the
 EMS the mortality rate remains high [1]. Due to the dramatic consequence of SCA,
 understanding of pathophysiological mechanisms and early identification of etiology is
 essential to improve outcome.

 SCA due to VF may be the presenting symptom of acute myocardial ischemia or may be a
 consequence of scarring due to a previous myocardial infarction (MI). Cardiac troponin (c-Tn)
 is the most commonly used biomarker for diagnosing an acute myocardial infarction (AMI) [7].
 Although earlier detection of AMI may be obtained by the introduction of high sensitivity
 (hs)-cTn assays, there still remains a troponin-blind period very early after symptom onset
 [8, 9], with the need for serial blood sampling to diagnose or exclude an AMI [7, 9].
 Furthermore, there are challenges related to the specificity of elevated levels of hs-cTn
 [10, 11]. Therefore, measurement of hs-cTn in a single blood draw in the ambulance or at
 admission may not provide sufficient information for the diagnosis of AMI among patients with
 OHCA.

 Lately, several studies have demonstrated an incremental diagnostic value of copeptin when
 added to conventional cTn or hs-cTn for early detection of AMI [12, 13]. Copeptin levels peak
 early (0-1 h) after symptom onset and are already increased at the time of first medical
 contact in the ambulance for patients with MI [8]. Copeptin used in combination with hs-cTn
 may therefore improve the diagnosis of AMI in very early presenters, and help differentiating
 the underlying cause of SCD.

 Copeptin has also been demonstrated to be an independent predictor of adverse events
 following MI [14] and is shown to be associated with outcome after OHCA [15, 16]. Less is
 known about the prognostic value of troponins in patients experiencing a cardiac arrest (CA).
 Higher values of hs-cTnT are seen in one-year non-survivors as compared to survivors of OHCA,
 although not shown to be an independent predictor of 12-months survival [10]. In our study,
 the objective will be to evaluate the diagnostic and prognostic utility of hs-cTnT and
 copeptin in SCA patients.

 Patients with heart failure are at increased risk for ventricular arrhythmias and SCD. B-type
 natriuretic peptide (BNP) and N-terminal proBNP (NT-proBNP) have been demonstrated to be
 useful diagnostic tools to rule out both chronic and acute heart failure [17]. Little is
 known about the natural course of natriuretic peptides during a SCA event, but BNP is
 demonstrated to be an independent predictor of long-term mortality [18], as well as survival
 to hospital discharge after OHCA of cardiac origin [19]. There is also a well-documented
 association between BNP or NT-proBNP and the short- and long-term risk of death in patients
 with acute coronary syndrome (ACS) [20, 21]. In our study, we intend to investigate the
 diagnostic and prognostic utility of NT-proBNP sampled during or immediately after OHCA.

 The overall survival rate after OHCA is low. Even in successfully resuscitated patients
 admitted to the intensive care unit (ICU), the prognosis remains poor. Former studies have
 shown a marked activation of blood coagulation, with a concomitant inadequate activation of
 the endogenous fibrinolytic system, in resuscitated OHCA-patients [22-25]. Intravascular
 clotting and "no reflow" in the microvasculature represent a barrier to successful end-organ
 perfusion and may influence the outcome in cardiac arrest (CA) patients [26]. Understanding
 the pathophysiological mechanisms of CA is important to guide management and improve outcome.
 Plasma thrombin-antithrombin (TAT) complexes, fibrin monomers (FM) and D-dimer are used as
 specific markers of activated blood coagulation. Previous studies have shown markedly
 increased TAT-levels in patients with nontraumatic OHCA [22, 23]. Admission TAT is also shown
 to be a useful prognostic marker in resuscitated OHCA patients and is independently
 associated with survival after resuscitation from CA [24]. D-dimer levels are found to
 increase after CA and CPR [22, 27]. Accordingly, Adrie et al. [28] demonstrated high
 admission levels of D-dimer in all OHCA patients. Furthermore Szymanski et al. [29] reported
 higher D-dimer concentrations on admission to be a strong and independent predictor of
 mortality in OHCA patients. In our study, we intend to study the activation of blood
 coagulation, including both the extrinsic- and the intrinsic coagulation pathways, during and
 immediately after SCA with regard to outcome.

 Most interventions to date do not directly affect the transient pathophysiologic event
 initializing potentially fatal arrhythmias. Instead, they attempt to alter and prevent
 underlying disease like CAD. Animal studies have shown that fish oils are protective against
 ischemia-induced VF [30]. Support for these data comes from the Physicians' Health Study
 [31], which is a prospective study of 20 551 men aged 40 to 84, free of cardiovascular
 disease at baseline, with a follow-up period of 11 years. As compared to consumption of fish
 less than once a month, fish intake at least once per week was associated with a reduced risk
 of SCD (RR 0.48). In the same study there was no reduction in the risk of total myocardial
 infarction, non-sudden cardiac death or total cardiovascular mortality, and the protective
 effect of fish was suggested to be due to a reduction in fatal ventricular arrhythmias. It
 has been hypothesized that the lower risk of SCD with higher fish intake may be related to
 the long-chain n-3 polyunsaturated fatty acids (PUFAs) EPA and DHA found in fish. Consistent
 with this hypothesis are the observations from the physicians' Health Study [31] that the
 risk of SCD was significantly lower in subjects with blood n-3 FA levels in the highest as
 compared to the lowest quartile. The same potential effect of fish oils to protect against
 SCD was illustrated in the randomized, open-controlled GISSI-prevention study [32]. Patients
 with a recent myocardial infarction receiving n-3 FAs supplements had a significant lower
 incidence in the combined endpoint of death plus nonfatal infarction and nonfatal stroke at
 42 months (12.6 versus 13.9%). After adjustment for risk factors, all of the observed benefit
 was due to a 20 % reduction in the risk of death, mostly due to reduction in SCD. However, a
 study of 200 patients secured with an ICD (implantable cardioverter defibrillator) following
 an episode of ventricular tachycardia (VT) or VF, has not shown a reduction in the recurrence
 of these arrhythmias after supplementation with EPA/DHA. In that study there was actually a
 trend toward a higher incidence of VT/VF in patients randomized to EPA/ DHA substitution
 [33]. In that setting the underlying mechanism for the generation of VF might, however, not
 be ischemic.

 The exact mechanism by which FAs might protect against serious cardiac arrhythmias is not
 known. They are important constituents of cell membranes and may affect several
 electrophysiologic properties, such as resting potential, action potential, repolarization
 and refractory period. Alterations in cellular calcium concentration can contribute
 significantly to changes in both impulse generation and impulse conduction in myocardial
 cells. Incorporation of n-3 fatty acids in the cellular membrane is shown to affect membrane
 fluidity which in turn may have an influence on calcium entry or removal. An alternative
 mechanism may be changes effected by n-3 FAs on myocardial production of eicosanoids. In
 particular the inhibition of thromboxane A2 (TXA2) production is likely to be of significant
 pathophysiological benefit, since TXA2 is shown to be implicated in myocardial ischemia and
 arrhythmogenesis [34].

 A recent study by William S. Harris et al. [35] has shown that levels of EPA/ DHA in cell
 membranes of red blood cells (RBC EPA/ DHA) highly correlate with the cardiac EPA/ DHA level.
 The RBC response to supplementation was also very similar to that observed in the heart.
 Therefore RBC EPA+ DHA may serve as a useful surrogate of cardiac omega-3 fatty acid status.
 The investigators expect n-3 FAs to exert a membrane stabilizing effect during an ischemic
 episode, and hypothesize that patients suffering VF during the initial phase of their first
 AMI presentation have lower levels of RBC EPA/ DHA than matched controls.

 Over the last years vitamin D is another dietary supplement found to be associated with
 cardiovascular disease. This fat-soluble vitamin, primarily derived from sun-exposure and
 fatty fish, has been demonstrated to influence cardiac contractility and myocardial calcium
 homeostasis [36], and insufficiency of this vitamin may have deleterious effects on cardiac
 autonomic functions as evaluated by heart rate turbulence and heart rate variability [37]. In
 prospective studies, severe vitamin D deficiency has been strongly associated with total
 mortality, cardiovascular events and SCD [38-42]. In one study of 3299 patients who were
 routinely referred to coronary angiography, the authors demonstrated hazard ratios for death
 due to heart failure and for SCD of 2.84 (1.20-6.74) and 5.05 (2.13-11.97), respectively,
 when comparing patients with severe vitamin D deficiency [25(OH)D <25 nmol/liter)] with
 persons in the optimal range [25(OH)D ≥ 75 nmol/liter] [43]. Demonstrated effects on
 electrophysiology,contractility, and cardiac structure suggest that vitamin D deficiency
 might actually be a causal factor for development of cardiac diseases. The pronounced effect
 on SCD found in several studies might be an indication of a possible protective effect of
 high vitamin D-levels against ventricular arrhythmias. This is, however, not well studied and
 the optimal cut-off-value for protection is not well defined. Therefore, a comparison of the
 25-OH-vitamin D levels between different OHCA categories of patients, with and without an
 acute coronary event, may be appropriate.

 Statistical methods

 Statistical analysis will be performed using the statistical package SPSS (Statistical
 Package for the Social Sciences). A statistically significant level of p < 0.05 will be
 applied for all tests.

 EPA/ DHA and vitamin D in the different clinical patient categories will be compared to
 controls collected from the RACS (Risk markers in the Acute Coronary Syndromes) database
 (NCT00521976).

 Ethics and confidentiality

 The present study is conducted in accordance with the Helsinki Declaration of 1975 and later
 revisions and accepted by the Regional Board of Research Ethics as well as the Norwegian
 Health Authorities. Analytic data will be related to patient number and not to patient
 identity. According to Norwegian regulations, the family of non-survivors will be informed by
 the attending physician and the inclusion of patients needs to be documented in the hospital
 records. The family of the deceased is entitled to object to the use of any biological
 samples for research purposes. Patients regaining consciousness and mental capability during
 their hospital stay will be asked personally for a written informed consent. For the
 remaining survivors the next of kin will be asked for permission on behalf of the patient. If
 either the patient or the family refuses participation, blood samples already collected at
 resuscitation and admission will be destroyed.
Inclusion Criteria:

 1. Age > 18 years

 2. OHCA of assumed cardiac etiology

 3. Documented first recorded heart rythm

 Exclusion Criteria:

 1. Evidence of non-cardiac death (including cerebral etiology and pulmonary embolism)

 2. OHCA due to cardiac tamponade.