Risk Factors for Myocardial Infarction and Stroke Among Sepsis Survivors: A Competing Risks Analysis.

OBJECTIVES: Predictors for post-sepsis myocardial infarction (MI) and stroke are yet to be identified due to the competing risk of death. METHODS: This study included all hospitalized patients with sepsis from National Health Insurance Research Database of Taiwan between 2000 and 2011. The primary outcome was the first occurrence of MI and stroke requiring hospitalization within 180 days following hospital discharge from the index sepsis episode. The association between predictors and post-sepsis MI and stroke were analyzed using cumulative incidence competing risk model that controlled for the competing risk of death. RESULTS: Among 42 316 patients with sepsis, 1012 (2.4%) patients developed MI and stroke within 180 days of hospital discharge. The leading 5 predictors for post-sepsis MI and stroke are prior cerebrovascular diseases (hazard ratio [HR]: 2.02, 95% confidence interval [CI]: 1.74-2.32), intra-abdominal infection (HR: 1.94, 95% CI: 1.71-2.20), previous MI (HR: 1.81, 95% CI: 1.53-2.15), lower respiratory tract infection (HR: 1.62, 95% CI: 1.43-1.85), and septic encephalopathy (HR: 1.61, 95% CI: 1.26-2.06). CONCLUSIONS: Baseline comorbidities and sources of infection were associated with an increased risk of post-sepsis MI and stroke. The identified risk factors may help physicians select a group of patients with sepsis who may benefit from preventive measures, antiplatelet treatment, and other preventive measures for post-sepsis MI and stroke.

Impact of post-sepsis cardiovascular complications on mortality in sepsis survivors: a population-based study.

BACKGROUND: It remains unclear whether sepsis-related cardiovascular complications have an adverse impact on survival independent of pre-existing comorbidities. To investigate the survival impact of post-sepsis cardiovascular complications among sepsis survivors, we conducted a population-based study using the National Health Insurance Database of Taiwan. METHODS: We identified sepsis patients from the National Health Insurance Research Database of Taiwan using ICD-9-CM codes involving infection and organ dysfunction between 2000 and 2011. Post-sepsis incident myocardial infarction (MI) and stroke were ascertained by ICD-9-CM codes and antiplatelet treatment. We constructed a non-sepsis comparison cohort using propensity score matching to ascertain the association between sepsis and cardiovascular complications. Furthermore, we compared the 180-day mortality and 365-day mortality between patients surviving sepsis with or without post-sepsis MI or stroke within 70 days of hospital discharge. We constructed Cox regression models adjusting for pre-existing comorbidities to evaluate the independent survival impact of post-sepsis MI or stroke among sepsis survivors. RESULTS: We identified 42,316 patients hospitalized for sepsis, from which we matched 42,151 patients 1:1 with 42,151 patients hospitalized without sepsis. Compared to patients hospitalized without sepsis, patients hospitalized with sepsis had an increased risk of MI or stroke (adjusted odds ratio 1.72, 95% CI 1.60-1.85). Among 42,316 patients hospitalized for sepsis, 486 (1.15%) patients developed incident stroke and 108 (0.26%) developed incident MI within 70 days of hospital discharge. Compared to sepsis survivors without cardiovascular complications, sepsis survivors with incident MI or stroke had a higher mortality rate at 180 days (11.68% vs. 4.44%, P = 0.003) and at 365 days (16.75% vs. 7.11%, P = 0.005). Adjusting for age, sex, and comorbidities, post-sepsis MI or stroke was independently associated with increased 180-day (adjusted hazard ratio [HR] 2.16, 95% CI 1.69-2.76) and 365-day (adjusted HR 1.90, 95% CI 1.54-2.32) mortality. CONCLUSIONS: Compared to sepsis patients without incident MI or stroke, sepsis patients with incident MI or stroke following hospital discharge had an increased risk of mortality for up to 365 days of follow-up. This increased risk cannot be explained by pre-sepsis comorbidities.

Susceptible period for cardiovascular complications in patients recovering from sepsis.

BACKGROUND: Patients are at increased risk of cardiovascular complications while recovering from sepsis. We aimed to study the temporal change and susceptible periods for cardiovascular complications in patients recovering from sepsis by using a national database. METHODS: In this retrospective population-based cohort study, patients with sepsis were identified from the National Health Insurance Research Database in Taiwan. We estimated the risk of myocardial infarction (MI) and stroke following sepsis by comparing a sepsis cohort to a matched population and hospital control cohort. The primary outcome was first occurrence of MI or stroke requiring admission to hospital during the 180-day period following discharge from hospital after sepsis. To delineate the risk profile over time, we plotted the weekly risk of MI and stroke against time using the Cox proportional hazards model. We determined the susceptible period by fitting the 2 phases of time-dependent risk curves with free-knot splines, which highlights the turning point of the risk of MI and stroke after discharge from the hospital. RESULTS: We included 42 316 patients with sepsis; stroke developed in 831 of these patients and MI developed in 184 within 180 days of discharge from hospital. Compared with population controls, patients recovering from sepsis had the highest risk for MI or stroke in the first week after discharge (hazard ratio [HR] 4.78, 95% confidence interval [CI] 3.19 to 7.17; risk difference 0.0028, 95% CI 0.0021 to 0.0034), with the risk decreasing rapidly until the 28th day (HR 2.38, 95% CI 1.94 to 2.92; risk difference 0.0045, 95% CI 0.0035 to 0.0056) when the risk stabilized. In a repeated analysis comparing the sepsis cohort with the nonsepsis hospital control cohort, we found an attenuated but still marked elevated risk before day 36 after discharge (HR 1.32, 95% CI 1.15 to 1.52; risk difference 0.0026, 95% CI 0.0013 to 0.0039). The risk of MI or stroke was found to interact with age, with younger patients being associated with a higher risk than older patients (interaction p = 0.0004). INTERPRETATION: Compared with the general population with similar characteristics, patients recovering from sepsis had a markedly elevated risk of MI or stroke in the first 4 weeks after discharge from hospital. More close monitoring and pharmacologic prevention may be required for these patients at the specified time.

Nationwide Trend of Sepsis: A Comparison Among Octogenarians, Elderly, and Young Adults.

OBJECTIVE: We aimed to compare the sepsis incidence, mortality rates, and primary sites of infection among adult, elderly, and octogenarian patients with sepsis. DESIGN: Population-based cohort study. SETTING: The entire health insurance claims data of Taiwan, which enrolled 99.8% of the 23 million Taiwanese population. PATIENTS: Sepsis patients were identified by International Classification of Diseases, 9th Edition, Clinical Modification codes for both infection and organ dysfunction from January 1, 2002, to December 31, 2012. Patients were categorized into three age groups: 1) adults (18-64 yr); 2) elderly (65-84 yr); and 3) oldest old (≥ 85 yr). The 30-day all-cause mortality was verified by a linked national death certificate database. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: From 2002 to 2012, we identified 1,259,578 patients with sepsis, of which 417,328 (33.1%) were adults, 652,618 (51.8%) were elderly, and 189,632 (15.1%) were oldest old. We determined that the incidence of sepsis in the oldest old was 9,414 cases per 100,000 population on 2012, which was 31-fold greater than the adult incidence (303 cases per 100,000 population) and three-fold greater than the elderly incidence (2,908 cases per 100,000 population). Despite the increasing trend in incidence, the mortality decreased by 34% for adults, 24% for elderly, and 22% for oldest old. However, systemic fungal infection was disproportionately increased in oldest old patients (1.76% annual increase) and the elderly patients (1.00% annual increase). CONCLUSION: The incidence of sepsis is disproportionately increased in elderly and oldest old patients. Despite the increasing trend in incidence, the mortality rate in geriatric patients with sepsis has decreased. However, the increased incidence of fungal infections in the geriatric population warrants further attention.

Preadmission Use of Calcium Channel Blocking Agents Is Associated With Improved Outcomes in Patients With Sepsis: A Population-Based Propensity Score-Matched Cohort Study.

OBJECTIVES: Use of calcium channel blockers has been found to improve sepsis outcomes in animal studies and one clinical study. This study determines whether the use of calcium channel blockers is associated with a decreased risk of mortality in patients with sepsis. DESIGN: Population-based matched cohort study. SETTING: National Health Insurance Research Database of Taiwan. PATIENTS: Hospitalized severe sepsis patients identified from National Health Insurance Research Database by International Classification of Diseases, Ninth Revision, Clinical Modification codes. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The association between calcium channel blocker use and sepsis outcome was determined by multivariate-adjusted Cox proportional hazard models and propensity score analysis. To examine the influence of healthy user bias, beta-blocker was used as an active comparator. Our study identified 51,078 patients with sepsis, of which, 19,742 received calcium channel blocker treatments prior to the admission. Use of calcium channel blocker was associated with a reduced 30-day mortality after propensity score adjustment (hazard ratio, 0.94; 95% CI, 0.89-0.99), and the beneficial effect could extend to 90-day mortality (hazard ratio, 0.95; 95% CI, 0.89-1.00). In contrast, use of beta-blocker was not associated with an improved 30-day (hazard ratio, 1.06; 95% CI, 0.97-1.15) or 90-day mortality (hazard ratio, 1.00; 95% CI, 0.90-1.11). On subgroup analysis, calcium channel blockers tend to be more beneficial to patients with male gender, between 40 and 79 years old, with a low comorbidity burden, and to patients with cardiovascular diseases, diabetes, or renal diseases. CONCLUSIONS: In this national cohort study, preadmission calcium channel blocker therapy before sepsis development was associated with a 6% reduction in mortality when compared with patients who have never received calcium channel blockers.

Phosphatidylinositol 4,5-biphosphate (PIP2) modulates syntaxin-1A binding to sulfonylurea receptor 2A to regulate cardiac ATP-sensitive potassium (KATP) channels.

Cardiac sarcolemmal syntaxin (Syn)-1A interacts with sulfonylurea receptor (SUR) 2A to inhibit ATP-sensitive potassium (KATP) channels. Phosphatidylinositol 4,5-bisphosphate (PIP2), a ubiquitous endogenous inositol phospholipid, known to bind Kir6.2 subunit to open KATP channels, has recently been shown to directly bind Syn-1A in plasma membrane to form Syn-1A clusters. Here, we sought to determine whether the interaction between Syn-1A and PIP2 interferes with the ability of Syn-1A to bind SUR2A and inhibit KATP channel activity. We found that PIP2 dose-dependently reduced SUR2A binding to GST-Syn-1A by in vitro pulldown assays. FRET studies in intact cells using TIRFM revealed that increasing endogenous PIP2 levels led to increased Syn-1A (-EGFP) cluster formation and a severe reduction in availability of Syn-1A molecules to interact with SUR2A (-mCherry) molecules outside the Syn-1A clusters. Correspondingly, electrophysiological studies employing SUR2A/Kir6.2-expressing HEK cells showed that increasing endogenous or exogenous PIP2 diminished the inhibitory effect of Syn-1A on KATP currents. The physiological relevance of these findings was confirmed by ability of exogenous PIP2 to block exogenous Syn-1A inhibition of cardiac KATP currents in inside-out patches of mouse ventricular myocytes. The effect of PIP2 on physical and functional interactions between Syn-1A and KATP channels is specific and not observed with physiologic concentrations of other phospholipids. To unequivocally demonstrate the specificity of PIP2 interaction with Syn-1A and its impact on KATP channel modulation by Syn-1A, we employed a PIP2-insensitive Syn-1A-5RK/A mutant. The Syn-1A-5RK/A mutant retains the ability to interact with SUR2A in both in vitro binding and in vivo FRET assays, although as expected the interaction is no longer disrupted by PIP2. Interestingly, at physiological PIP2 concentrations, Syn-1A-5RK/A inhibited KATP currents to a greater extent than Syn-1A-WT, indicating that the inhibitory effect of Syn-1A on KATP channels is not due to direct competition between Syn-1A and Kir6.2 for PIP2 binding. At high-dose PIP2, however, inhibition of KATP currents by Syn-1A-5RK/A was greatly reduced, likely overridden by the direct activating effect of PIP2 on KATP channels. Finally, depleting endogenous PIP2 with polyphosphoinositide phosphatase synaptojanin-1 known to disperse Syn-1A clusters, freed Syn-1A from Syn-1A clusters to bind SUR2A, causing optimal inhibition of KATP channels. These results taken together led us to conclude that PIP2 affects cardiac KATP channels not only by its actions on the channel directly but also by multi-modal effects of dynamically modulating Syn-1A mobility from Syn-1A clusters and thereby the availability of Syn-1A to inhibit KATP channels via interaction with SUR2A on the plasma membrane.

Phosphatidylinositol 4,5-biphosphate (PIP2) modulates interaction of syntaxin-1A with sulfonylurea receptor 1 to regulate pancreatic ß-cell ATP-sensitive potassium channels.

In ß-cells, syntaxin (Syn)-1A interacts with SUR1 to inhibit ATP-sensitive potassium channels (KATP channels). PIP2 binds the Kir6.2 subunit to open KATP channels. PIP2 also modifies Syn-1A clustering in plasma membrane (PM) that may alter Syn-1A actions on PM proteins like SUR1. Here, we assessed whether the actions of PIP2 on activating KATP channels is contributed by sequestering Syn-1A from binding SUR1. In vitro binding showed that PIP2 dose-dependently disrupted Syn-1A·SUR1 complexes, corroborated by an in vivo Forster resonance energy transfer assay showing disruption of SUR1(-EGFP)/Syn-1A(-mCherry) interaction along with increased Syn-1A cluster formation. Electrophysiological studies of rat ß-cells, INS-1, and SUR1/Kir6.2-expressing HEK293 cells showed that PIP2 dose-dependent activation of KATP currents was uniformly reduced by Syn-1A. To unequivocally distinguish between PIP2 actions on Syn-1A and Kir6.2, we employed several strategies. First, we showed that PIP2-insensitive Syn-1A-5RK/A mutant complex with SUR1 could not be disrupted by PIP2, consequently reducing PIP2 activation of KATP channels. Next, Syn-1A·SUR1 complex modulation of KATP channels could be observed at a physiologically low PIP2 concentration that did not disrupt the Syn-1A·SUR1 complex, compared with higher PIP2 concentrations acting directly on Kir6.2. These effects were specific to PIP2 and not observed with physiologic concentrations of other phospholipids. Finally, depleting endogenous PIP2 with polyphosphoinositide phosphatase synaptojanin-1, known to disperse Syn-1A clusters, freed Syn-1A from Syn-1A clusters to bind SUR1, causing inhibition of KATP channels that could no longer be further inhibited by exogenous Syn-1A. These results taken together indicate that PIP2 affects islet ß-cell KATP channels not only by its actions on Kir6.2 but also by sequestering Syn-1A to modulate Syn-1A availability and its interactions with SUR1 on PM.

Syntaxin-1A inhibits KATP channels by interacting with specific conserved motifs within sulfonylurea receptor 2A.

We previously demonstrated that syntaxin (Syn)-1A is present in the sarcolemma of rat cardiomyocytes and binds sulfonylurea receptor (SUR) 2A nucleotide binding folds (NBFs) to inhibit ATP-sensitive potassium (K(ATP)) channel. Here, we examined for the precise domains within the NBFs of SUR2A that may interact with Syn-1A. Specifically, we tested truncated NBF protein segments encompassing the conserved motifs Walker A (W(A)), signature/Linker (L), and Walker B (W(B)). In vitro binding results indicate that the domains encompassing W(A) and L of NBF-1 and all three conserved motifs of NBF-2 bound Syn-1A. Electrophysiological studies, employing inside-out patch-clamp recordings from SUR2A/Kir6.2 expressing HEK cells and mouse cardiomyocytes, show that W(B) and L of NBF-1 and all three NBF-2 truncated protein segments reduced Syn-1A inhibition of SUR2A/K(ATP) channels. Remarkably, these same NBF-1 and -2 truncated proteins could independently disrupt the intimate FRET interactions of full length SUR2A (-mCherry) and Syn-1A (-EGFP). These results taken together indicate that Syn-1A possibly maintains inhibition of cardiac ventricular K(ATP) channels by binding to large regions of NBF-1 and NBF-2 to stabilize the NBF-1-NBF-2 heterodimer formation and prevent ATP-binding and ATP hydrolysis. Since K(ATP) channels are closely coupled to metabolic states, we postulate that these very intimate Syn-1A-SUR2A interactions are critically important for myocardial protection during stress, in which profound changes in metabolic factors (pH, ATP) could modulate these Syn-1A-SUR2A interactions.

SNARE protein regulation of cardiac potassium channels and atrial natriuretic factor secretion.

Coordinated cardiac ion channel gating is fundamental for generation of action potential and excitability throughout the myocardium. The interaction of pore-forming ion channels with auxiliary subunits can regulate surface expression, localization and anchoring of these channels to plasma membrane. SNARE (soluble N-ethylmaleimide sensitive factors attachment protein or SNAP receptor) proteins mediate the targeting, docking, and fusion of intracellular vesicles for exocytotic release of neurotransmitters and hormones. In secretory neurons and neuroendocrine cells, some voltage-gated channels are physically coupled with SNARE proteins, resulting in alterations in channel gating and trafficking. Coupling of SNARE proteins to membrane ion channels is however not unique to secretory cells. We have demonstrated the expression of SNARE proteins in rodent myocardial tissue, and more importantly, functional interaction of SNARE proteins with cardiac K(ATP) and K(v) (K(v)1.2, K(v)2.1, K(v)4.2, K(v)4.3, and K(v)11.1) channels. SNARE proteins, therefore, have similar fundamental functions in ion channel trafficking and regulation per se, independent of secretion. We now review the body of work of SNARE protein regulation on membrane ion channels in the heart.