QT interval prolongation

Seasonal effects of ambient PM2.5 on the cardiovascular system of hyperlipidemic mice

People in polluted communities are often exposed to both PM and ozone (O₃), albeit not always simultaneously; an important question is whether exposure to particles with seasonal compositional differences can influence biological outcomes. We addressed this question using a mouse model of cardiovascular disease by contrasting the health outcomes of exposures to particles formed or aged during periods of relatively high photochemical activity (i.e. spring/summer), which has increased ambient O₃ concentrations, with outcomes of exposures to fall/winter particles which are associated with lower O₃ concentrations. Electrocardiographs (ECGs) and blood pressures (BPs) were acquired following exposures to concentrated ambient particles (CAPs). ECGs were analyzed to changes in specific waveform parameters and changes in heart rate variability (HRV). Exposures elicited several types of waveform abnormalities that were associated with seasonal differences in particle constituents. Alterations in R-R interval and P-R interval were seen following exposure to summer CAPs but not fall CAPs and differential responses were seen in the corrected Q-T interval following the two seasonal exposures. Measures of HRV increased after exposure to summer CAPs compared to air-exposed controls but not following the winter CAPs exposure. There were chemical differences with respect to the organic constituents in ambient particles between summer and fall aerosol. The oxygen to carbon ratios (O:C) were generally higher in the spring and summer than in the fall, consistent with seasonal differences in atmospheric photochemical activity. Seasonal differences in atmospheric photochemical activity can modify ambient aerosol composition and can alter biological responses in the cardiovascular system. The results from this study confirm that ambient photochemical activity can alter the toxicity of ambient PM. Regional and seasonal differences in PM_2.5 composition should be important considerations when evaluating the effects of PM exposure on cardiovascular health.Implications: Particles formed during periods of high photochemical activity (e.g. spring/summer) elicit more adverse cardiovascular health effects than particles formed during periods of low photochemical activity (e.g. fall/winter). Seasonal differences in atmospheric photochemical activity modified ambient aerosol composition and worsened cardiovascular responses. These results can inform regulatory agencies and may help design air quality regulations for PM2.5 that consider seasonal and regional variations.

Low Calcium Dialysate Increases Cardiac Relaxation in CAPD Patients

Objective

To establish whether changes in serum calcium affect left ventricular (LV) function in continuous ambulatory peritoneal dialysis (CAPD) patients.

Methods

This study was conducted on 28 clinically stable CAPD patients (11 females, 17 males). Left ventricular relaxation and systolic function were echocardiographically examined in all patients during standard dialysate (containing 1.75 mmol/L calcium) treatment. All patients were then changed to low calcium dialysate (1.25 mmol/L calcium) for 1 month and all patients were re-examined echocardiographically. Decrement in isovolumic relaxation time (IVRT) and deceleration time (DT), and increment in the ratio of peak early to peak late diastolic velocities (E/Amax) were admitted as indexes showing improvement in LV relaxation. 17 age- and sex-matched controls were also echocardiographically examined.

Results

Deceleration time, interventricular septal thickness at systole (IVSTS) and diastole (IVSTD), and posterior wall thickness at systole (PWS) and diastole (PWD) were higher in CAPD patients using standard dialysate than in normal controls. With the use of low calcium dialysate, DTs were similar but IVSTS, IVSTD, PWS, and PWD values remained higher. In normal controls, E/Amax values were higher than those in CAPD patients using standard dialysate ( p < 0.001) and low calcium dialysate ( p = 0.009). Serum intact parathyroid hormone level, weight, clinical volume status, and blood pressure were similar throughout the study period. Serum ionized calcium levels were decreased significantly during low calcium dialysate treatment. The changes in IVRT, DT, and E/Amax suggest improvement in LV relaxation during low calcium dialysate treatment.

Conclusion

Left ventricular relaxation is increased with the use of low calcium dialysate compared with standard dialysate treatment. The idea of possible beneficial effects of increment in LV relaxation on cardiovascular morbidity and mortality deserves further studies.

Association Between Particulate Air Pollution and QT Interval Duration in an Elderly Cohort

BACKGROUND

Short-term fine particulate matter (PM2.5) exposure has been linked with increased QT interval duration, a marker of ventricular repolarization and a risk factor for cardiac arrhythmia and sudden death, in several studies. Only one previous study evaluated whether long-term PM exposure is related to the QT interval. We aim to evaluate whether subchronic and long-term exposure to PM2.5 at home is linked with QT duration in an elderly cohort.

METHODS

We measured heart-rate corrected QT interval duration among 404 participants from the Greater Boston area between 2003 and 2011. We modeled residential PM2.5 exposures using a hybrid satellite- and land use-based model. We evaluated associations between moving averages of short-term (1-2 days), subchronic (3-28 days), and long-term (1 year) pollutant exposures and corrected QT duration using linear mixed models. We also evaluated effect modification by oxidative stress genetic score using separated regression models and interaction terms.

RESULTS

We observed positive associations between subchronic and long-term PM2.5 exposure and corrected QT duration, with the strongest results for longer-term exposures. For example, a one standard deviation increase in 1-year PM2.5 was associated with a 6.3 ms increase in corrected QT (95% confidence interval: 1.8, 11). We observed somewhat greater effects among subjects with higher (8.5 ms) rather than lower (3.1 ms) oxidative stress allelic profiles (P interaction = 0.25).

CONCLUSIONS

PM2.5 was associated with increased corrected QT duration in an elderly cohort. While most previous studies focused on short-term air pollution exposures, our results suggest that longer-term exposures are associated with cardiac repolarization.

Association between low-level environmental arsenic exposure and QT interval duration in a general population study

High-level arsenic exposure is consistently associated with QT prolongation, a risk factor for arrhythmia and sudden cardiac death. Arsenic may act on QT by increasing cardiac calcium currents. The authors hypothesized that low-level arsenic exposure would be associated with QT duration and that this effect would be stronger among persons not using calcium channel blockers. They performed a cross-sectional analysis in elderly men from the Normative Aging Study to analyze associations between toenail arsenic and QT and heart rate-corrected QT (QTc) durations and to examine effect modification by calcium channel blocker use, using linear regression and adjusting for potential confounders. Participants were examined in Boston, Massachusetts, between 2000 and 2002 or in 2006. An interquartile range increase in arsenic concentration was associated with a 3.8-millisecond increase in QT (95% confidence interval: 0.82, 6.8) and a 2.5-millisecond increase in QTc (95% confidence interval: 0.11, 4.9). There was no evidence of effect modification by medication use for either QT (P = 0.93) or QTc (P = 0.58). The authors observed positive associations between a biomarker of arsenic exposure and QT duration but found no evidence of effect modification by calcium channel blocker use, possibly because of modest power.