Electrocardiographic markers of sudden death

Beat-to-beat blood pressure variability in patients with obstructive sleep apnea

STUDY OBJECTIVES

Cardiovascular comorbidities in obstructive sleep apnea (OSA) are difficult to treat, perhaps due to autonomic dysfunction. We assessed beat-to-beat blood pressure (BP) variability (BPV) in OSA while considering other markers derived from electrocardiogram and continuous BP signals.

METHODS

We studied 66 participants (33 participants with OSA: respiratory event index [mean ± SEM]: 21.1 ± 2.7 events/h; 12 females, aged 51.5 ± 2.4 years; body mass index: 32.8 ± 1.4 kg/m²; 33 healthy controls: 20 females; aged 45.3 ± 2.4 years; body mass index: 26.3 ± 0.7 kg/m²). We collected 5-minute resting noninvasive beat-to-beat BP and electrocardiogram values. From BP, we derived systolic, diastolic, and mean BP values, and calculated variability as standard deviations (systolic BPV, diastolic BPV, BPV). We also calculated diastole-to-systole time (time to peak). From the electrocardiogram, we derived QRS markers and calculated heart rate and heart rate variability. We performed a multivariate analysis of variance based on sex and group (OSA vs control), with Bonferroni-corrected post hoc comparisons (P ≤ .05) between groups. We calculated correlations of BPV with biological variables.

RESULTS

Multivariate analysis of variance showed effects of diastolic BPV and BPV in OSA; post hoc comparisons revealed high diastolic BPV and BPV only in female participants with OSA vs controls. QRS duration was higher in OSA, with post hoc comparisons showing the effect only in males. BPV correlated positively with heart rate variability in controls but not in participants with OSA. BPV correlated positively with time to peak in females with OSA and OSA combined, whereas there was no BPV-time-to-peak correlation in healthy participants.

CONCLUSIONS

The findings show sex-specific autonomic dysfunction reflected in beat-to-beat BP in OSA. The higher BPV may reflect poor baroreflex control or vascular damage in OSA, which are potential precursors to cardiovascular complications.

Association between QRS duration and obstructive sleep apnea

BACKGROUND

Both obstructive sleep apnea (OSA) and prolonged QRS duration are associated with hypertension, heart failure, and sudden cardiac death. However, possible links between QRS duration and OSA have not been explored.

METHODS

Cross-sectional study of 221 patients who underwent polysomnography at our center. Demographics, cardiovascular risk factors and ECG were collected to explore a relationship between OSA and QRS duration.

RESULTS

The apnea-hypopnea index (AHI) was positively correlated with QRS duration (r = 0.141, p = 0.03). Patients were divided into 3 groups: AHI < 5 (61), AHI 5-29 (104), and AHI > 30 (55). The mean QRS duration prolonged significantly as OSA worsened (AHI < 5, 85 ± 9.5; AHI 5-29, 89 ± 11.9; and AHI > 30, 95 ± 19.9 ms, p = 0.001). QRS ≥ 100 ms was present in 12.7% of patients with severe OSA compared with 0% in the rest of the sample (p < 0.0001). After adjustment for age, race, and cardiovascular risk factors, this association remained significant in women but not in men.

CONCLUSION

QRS duration and OSA were significantly associated. Severity of OSA independently predicted prolonged QRS in women but not men. Nevertheless, prolongation of QRS duration in either sex may potentiate arrhythmic risks associated with OSA.

Sudden cardiac death: epidemiology and risk factors

Sudden cardiac death (SCD) is an important public-health problem with multiple etiologies, risk factors, and changing temporal trends. Substantial progress has been made over the past few decades in identifying markers that confer increased SCD risk at the population level. However, the quest for predicting the high-risk individual who could be a candidate for an implantable cardioverter-defibrillator, or other therapy, continues. In this article, we review the incidence, temporal trends, and triggers of SCD, and its demographic, clinical, and genetic risk factors. We also discuss the available evidence supporting the use of public-access defibrillators.

Spatial QRS-T angle in peritoneal dialysis patients: association with carotid artery atherosclerosis, coronary artery calcification and troponin T

BACKGROUND

Abnormal values of the spatial angle between the directions of ventricular depolarization and repolarization (QRS-T) predict potently arrhythmic events and mortality in various patients groups. The study was designed to estimate QRS-T in a group of peritoneal dialysis (PD) patients, and to assess the possible association between QRS-T and coronary artery calcification (CAC), atherosclerosis, and some biochemical measurements.

METHODS

The angular differences between the maximum spatial QRS and T vectors were reconstructed from ECGs in 57 selected PD patients and in 54 controls. In patients CAC score was performed by using multi-row computed tomography. Atherosclerotic disease was assessed by measuring carotid arteries' intima-media thickness (IMT) and plaque score (sum of the maximum thicknesses in mm of all plaques on both sides) by using an ultrasound scanner.

RESULTS

QRS-T was higher in patients compared with controls (34.79% B111.97 and 14.95% B17.87 respectively; P < 0.001). Median CAC score equalled 104.5 Agatson units (Au) (range, 0-2478). IMT was 0.832% B10.208, and atherosclerotic plaques were detected in 82.5% of patients. The plaque score was 7.97% B14.49. QRS-T was higher in patients with CAC score >400 Au compared with patients with CAC score <400 Au (P = 0.011). The results of univariate linear regression analysis showed correlation between QRT-T and dialysis duration (r = 0.305, P = 0,020), LVMI (r = 0.311, P = 0.017), HDL (r = -0.361, P = 0.006), cTnT (r = 0.442, P < 0.001), plaque score (r = 0.403, P = 0.001) and CAC score (r = 0.451, P < 0.001). On multivariate analysis, CAC score, plaque score and troponine T were found to be independent predictors of QRS-T values.

CONCLUSIONS

QRS-T is high in PD patients and is mainly associated with coronary artery calcium burden, atherosclerosis and troponin T elevation. The possible clinical importance of the higher QRS-T in PD patients remains to be confirmed in further studies.

The electrocardiogram in the patient with syncope

Syncope is a common and challenging presentation for the emergency physician. Various investigators have developed clinical risk score and clinical decision rules which are designed to identify the population at highest risk for adverse events. In each of these clinical decision tools, the electrocardiogram (ECG) is one of the key clinical variables used to evaluate the patient. Certain electrocardiographic presentations in the patient with syncope will not only provide a reason for the loss of consciousness but also guide early therapy and disposition in this individual. Bradycardia, atrioventricular block, intraventricular conduction abnormality, and tachydysrhythmia in the appropriate clinical setting provide an answer to the clinician for the syncopal event. Morphologic findings suggesting the range of cardiovascular malady are also encountered; these entities are far ranging, including the various ST-segment and T-wave abnormalities of acute coronary syndrome, ventricular preexcitation as seen in the Wolff-Parkinson-White syndrome, Brugada syndrome with the associated tendency for sudden death, prolonged QT interval common in the diverse long QT interval presentations, and right ventricular hypertrophy suggestive of hypertrophic cardiomyopathy. This review discusses the ECG in the patient with syncope. The general use of the 12-lead ECG in this patient population is discussed. Furthermore, specific electrocardiographic presentations seen in the patient with syncope are also reviewed.