Changes of the T-wave amplitude and angle: an early marker of altered ventricular repolarization in hypertension

Early exposure to mercury and cardiovascular function of seven-year old children in Guadeloupe (French West Indies)

BACKGROUND

The cardiotoxicity of prenatal exposure to mercury has been suggested in populations having regular contaminated seafood intake, though replications in the literature are inconsistent.

METHODS

The Timoun Mother-Child Cohort Study was set up in Guadeloupe, an island in the Caribbean Sea where seafood consumption is regular. At seven years of age, 592 children underwent a medical examination, including cardiac function assessment. Blood pressure (BP) was taken using an automated blood pressure monitor, heart rate variability (HRV, 9 parameters) and electrocardiogram (ECG) characteristics (QT, T-wave parameters) were measured using Holter cardiac monitoring during the examination. Total mercury concentrations were measured in cord blood at birth (median = 6.6 μg/L, N = 399) and in the children's blood at age 7 (median = 1.7 μg/L, N = 310). Adjusted linear and non-linear modelling was used to study the association of each cardiac parameter with prenatal and childhood exposures. Sensitivity analyses included co-exposures to lead and cadmium, adjustment for maternal seafood consumption, selenium and polyunsaturated fatty acids (n3-PUFAs), and for sporting activity.

RESULTS

Higher prenatal mercury was associated with higher systolic BP at 7 years of age (βlog2 = 1.02; 95% Confidence Interval (CI) = 0.10, 1.19). In boys, intermediate prenatal exposure was associated with reduced overall HRV and parasympathetic activity, and longer QT was observed with increasing prenatal mercury (βlog2 = 4.02; CI = 0.48, 7.56). In girls, HRV tended to increase linearly with prenatal exposure, and no association was observed with QT-wave related parameters. Mercury exposure at 7 years was associated with decreased BP in girls (βlog2 = -1.13; CI = -2.22, -0.004 for diastolic BP). In boys, the low/high-frequency (LF/HF) ratio increased for intermediate levels of exposure.

CONCLUSION

Our study suggests sex-specific and non-monotonic modifications in some cardiac health parameters following prenatal exposure to mercury in pre-pubertal children from an insular fish-consuming population.

Exploring vectorcardiography: An extensive vectocardiogram analysis across age, sex, BMI, and cardiac conditions

BACKGROUND

The vectocardiogram (VCG) offers a three-dimensional view of the heart's electrical activity, yet many VCG parameters remain unexplored in diverse clinical contexts.

OBJECTIVES

This study aims to explore the relationships between various VCG parameters and specific patient characteristics.

METHODS

ECG signals from adults were transformed into VCGs utilizing the Kors matrix, yielding 315 parameters per patient from the P, QRS and T loops. Univariable analysis, circular statistics, and stepwise logistic regression were employed to examine the relationships between VCG parameters and factors such as age, sex, BMI, hypertension, echocardiographic ischemic heart disease (Echo-IHD), and left ventricular hypertrophy (Echo-LVH).

RESULTS

We included 664 adults and considered an alpha value of 0.05 and a power of 90%. The study revealed significant associations, such as age with P loop roundness index (RI) (OR = 3.825, 95% confidence interval [95%CI] = 2.079-7.04), male sex with QRS loop RI (OR = 6.08, 95%CI = 1.835-20.153), abnormal BMI with the T loop's RI (OR = 0.544, 95%CI = 0.325-0.909), hypertension with the T loop planarity index (PI) (OR = 8.01, 95%CI = 2.134-30.117), Echo-IHD with QRS loop curvature at the 4/10th segment (OR = 7.58, 95%CI = 1.954-29.458), and Echo-LVH with the T loop lag-1/10 dihedral angle (OR = 10.3, 95%CI = 1.822-58.101). In the study, several additional VCG parameters demonstrated statistically significant, albeit smaller, associations with patient demographics and cardiovascular conditions.

CONCLUSIONS

The findings enhance our understanding of the intricate relationships between VCG parameters and patient characteristics, emphasizing the potential role of VCG analysis in assessing cardiovascular diseases. These insights may guide future research and clinical applications in cardiology.

Optimizing ECG to detect echocardiographic left ventricular hypertrophy with computer-based ECG data and machine learning

BACKGROUND

Left ventricular hypertrophy detected by echocardiography (Echo-LVH) is an independent predictor of mortality. Integration of the Philips DXL-16 algorithm into the electrocardiogram (ECG) extensively analyses the electricity of the heart. Machine learning techniques such as the C5.0 could lead to a new decision tree criterion to detect Echo-LVH.

OBJECTIVES

To search for a new combination of ECG parameters predictive of Echo-LVH. The final model is called the Cardiac Hypertrophy Computer-based model (CHCM).

METHODS

We extracted the 458 ECG parameters provided by the Philips DXL-16 algorithm in patients with Echo-LVH and controls. We used the C5.0 ML algorithm to train, test, and validate the CHCM. We compared its diagnostic performance to validate state-of-the-art criteria in our patient cohort.

RESULTS

We included 439 patients and considered an alpha value of 0.05 and a power of 99%. The CHCM includes T voltage in I (≤0.055 mV), peak-to-peak QRS distance in aVL (>1.235 mV), and peak-to-peak QRS distance in aVF (>0.178 mV). The CHCM had an accuracy of 70.5% (CI95%, 65.2-75.5), a sensitivity of 74.3%, and a specificity of 68.7%. In the external validation cohort (n = 156), the CHCM had an accuracy of 63.5% (CI95%, 55.4-71), a sensitivity of 42%, and a specificity of 82.9%. The accuracies of the most relevant state-of-the-art criteria were: Romhilt-Estes (57.4%, CI95% 49-65.5), VDP Cornell (55.7%, CI95%47.6-63.7), Cornell (59%, CI95%50.8-66.8), Dalfó (62.9%, CI95%54.7-70.6), Sokolow Lyon (53.9%, CI95%45.7-61.9), and Philips DXL-16 algorithm (54.5%, CI95%46.3-62.5).

CONCLUSION

ECG computer-based data and the C5.0 determined a new set of ECG parameters to predict Echo-LVH. The CHCM classifies patients as Echo-LVH with repolarization abnormalities or LVH with increased voltage. The CHCM has a similar accuracy, and is slightly more sensitive than the state-of-the-art criteria.

Prevalence and associated factors of Electrocardiogram abnormalities in patients with systemic lupus erythematosus: a machine learning study

OBJECTIVES

Electrocardiogram (ECG) abnormalities are predictive of subsequent cardiovascular events. Cardiac involvement is common in systemic lupus erythematosus (SLE). We aimed to determine the prevalence of ECG abnormalities in SLE patients and to examine the factors associated with ECG abnormalities with machine learning approaches.

METHODS

Consecutive SLE patients' records were retrieved from the database of the hospital for the cross-sectional study. Abnormal ECGs with clinical significance were grouped into tachyarrhythmias, atrioventricular block, non-specific ST-segment changes, T-wave abnormalities, ventricular hypertrophy, axis deviation, bundle branch block, and QT interval prolongation. Associated factors of the most common ECG abnormalities were assessed by comparing logistic regression and four other machine learning approaches.

RESULTS

Two hundred ninety-nine patients were enrolled. One hundred twenty-eight out of them were clinically significant abnormalities. T-wave changes (52.3%), non-specific ST-T changes (26.6%), and prolonged QT interval (8.6%) were the most prevalent abnormalities among patients with abnormal ECG. Random forest models had the best performance in the discovery of associated factors. Age, disease duration, ANA titer, disease activity (SLEDAI-2K) were associated with non-specific ST-T changes, prolonged QT interval, and T-wave changes. Hypertension, positive anti-SSA, and secondary Sjögren syndrome were influential factors for non-specific ST-T changes, prolonged QT interval, and T-wave changes specifically.

CONCLUSION

ST-T changes/T-wave changes were the most common abnormalities seen in ECGs of SLE patients. Our finding suggests that age, longer disease duration, higher disease activity, hypertension, anti-SSA antibody positive, and secondary Sjögren syndrome are important, influential factors for these ECG abnormalities.

T-wave and its association with myocardial fibrosis on cardiovascular magnetic resonance examination

Background

Risk stratification in non‐ischemic myocardial disease poses a challenge. While cardiovascular magnetic resonance (CMR) is a comprehensive tool, the electrocardiogram (ECG) provides quick impactful clinical information. Studying the relationships between CMR and ECG can provide much‐needed risk stratification. We evaluated the electrocardiographic signature of myocardial fibrosis defined as presence of late gadolinium enhancement (LGE) or extracellular volume fraction (ECV) ≥29%.

Methods

We evaluated 240 consecutive patients (51% female, 47.1 ± 16.6 years) referred for a clinical CMR who underwent 12‐lead ECGs within 90 days. ECG parameters studied to determine association with myocardial fibrosis included heart rate, QRS amplitude/duration, T‐wave amplitude, corrected QT and QT peak, and Tpeak‐Tend. Abnormal T‐wave was defined as low T‐wave amplitude ≤200 µV or a negative T wave, both in leads II and V5.

Results

Of the 147 (61.3%) patients with myocardial fibrosis, 67 (28.2%) had ECV ≥ 29%, and 132 (54.6%) had non‐ischemic LGE. An abnormal T‐wave was more prevalent in patients with versus without myocardial fibrosis (66% versus 42%, p < .001). Multivariable analysis demonstrated that abnormal T‐wave (OR 1.95, 95% CI 1.09–3.49, p = .03) was associated with myocardial fibrosis (ECV ≥ 29% or LGE) after adjustment for clinical covariates (age, gender, history of hypertension, and heart failure). Dynamic nomogram for predicting myocardial fibrosis using clinical parameters and the T‐wave was developed: https://normogram.shinyapps.io/CMR_Fibrosis/.

Conclusion

Low T‐wave amplitude ≤ 200 µV or negative T‐waves are independently associated with myocardial fibrosis. Prospective evaluation of T‐wave amplitude may identify patients with a high probability of myocardial fibrosis and guide further indication for CMR.

Prognostic significance of a low T/R ratio in Brugada syndrome

OBJECTIVES

To determine the prognostic value of a low T/R ratio, defined as the amplitude ratio between the T waves and the R waves, in patients (pts) with a spontaneous type-1 Brugada pattern (SBT1).

BACKGROUND

Abnormalities of myocardial repolarization may play a key role in the initiation of ventricular fibrillation (VF) in Brugada syndrome (BrS). Recent studies have shown that the height of the T waves and the T/R ratio are inversely proportional to sudden cardiac arrest (SCA) risk in early repolarization syndrome and hypertrophic cardiomyopathy.

METHODS

In an international retrospective study, we reviewed 115 pts. (105 males, 91.3%). 45 had VF and/or SCA (38.7 ± 11.5 years old, all males), while 70 (49.3 ± 12.0 years, 10 women) remained free of ventricular arrhythmia. 6 ECG markers plus the T/R ratio in leads V5 & II were studied.

RESULTS

The T/R ratio among leads II & V5 was significantly lower in the VF/SCA group (0.24 [0.14; 0.38]vs. 0.34 [0.24; 0.45]; p = 0.006). 44.4% of pts. in the VF/SCA group had a lowest T/R ratio among leads II & V5 ≤ 0.17 compared to 11.4% in the non-VF/SCA group (p < 0.001). In multivariate analysis, a lowest T/R ratio among leads II & V5 ≤ 0.17 was independently associated with VF/SCA (OR 6.10, 95% CI 1.92-19.40; p = 0.002). Type 1 Brugada pattern in the peripheral leads (OR 10.78) and early repolarization (OR 3.60) were other independent markers of VF/SCA.

CONCLUSION

A low T/R ratio among leads II & V5 is an independent marker for VF/SCA risk in patients with type-1 Brugada pattern.

Vectorcardiography Findings Are Associated with Recurrent Ventricular Arrhythmias and Mortality in Patients with Heart Failure Treated with Implantable Cardioverter-Defibrillator Device

BACKGROUND

There is a need for refined risk stratification of sudden cardiac death and prediction of ventricular arrhythmias to correctly identify patients who are expected to benefit the most from implantable cardioverter-defibrillator (ICD) therapy.

METHODS

We conducted a registry-based retrospective observational study on patients with either ischemic (ICMP) or nonischemic dilated cardiomyopathy (NICMP) treated with ICD between 2002 and 2013 at a tertiary referral center. We evaluated 3 vectorcardiography (VCG) indices; spatial QRS-T angle, QRS vector magnitude (QRSvm), and T-wave vector magnitude (Twvm), and their association with all-cause mortality and ventricular arrhythmias. The VCG indices were automatically computed from resting 12-lead electrocardiograms before ICD implantation.

RESULTS

178 patients were included in the study; 53.4% had ICMP, 79.2% were male, and mean ejection fraction was 27.4%. During the follow-up (median 89 months), 40 patients (23%) died; 31% had appropriate ICD therapy. In multivariate analysis with dichotomized variables, QRS-T angle >152° and Twvm <0.38 mV were significantly associated with increased mortality: HR 2.64 (95% CI 1.14-6.12, p = 0.02) and HR 5.30 (95% CI 2.31-12.11, p < 0.001), respectively. QRSvm <1.54 mV was borderline significant with mortality outcome (p = 0.10). The composite score of all 3 VCG indices, a score of 3, conferred an increased risk of mortality (including heart failure mortality) in multivariate analysis: HR 13.80 (95% CI 3.44-55.39, p < 0.001).

CONCLUSION

The spatial QRS-T angle and Twvm are emerging VCG indices which are independently associated with mortality in patients with reduced left ventricular ejection fraction due to ICMP or NICMP. Using a composite score of all 3 vector indices, a maximum score was associated with poor long-term survival.

Changes on the electrocardiogram in anorexia nervosa: A case control study

PURPOSE

Anorexia nervosa is a complex psychiatric condition with increased mortality. The electrocardiogram (ECG) may show repolarization changes which may associate with an increased risk of sudden death. Up to 80% of patients may be prescribed psychopharmacotherapies which alter the ECG, potentially compounding arrhythmic risk. This study aimed to describe and improve understanding of ECG changes in eating disorders and assess the effect of psychopharmacotherapies.

METHODS

Adolescent patients diagnosed with anorexia nervosa were reviewed. ECGs were reviewed by blinded expert reviewers, and repolarization parameters were compared to healthy controls. Patients on and off psychopharmacotherapies were compared.

RESULTS

Thirty-eight anorexia nervosa patients off psychopharmacotherapies were age matched to 53 healthy controls. Heart rate was lower in anorexia nervosa patients (56 vs. 74 bpm, p < 0.001). The absolute QT interval was longer in patients compared to controls (408 vs. 383 ms, p < 0.001), but the QTc by Hodges' formula was similar between groups (401 vs. 408 ms, p = 0.16). The prevalence of T-wave flattening and inversion was also similar between groups (13% vs. 4%, p = 0.12) and T-peak to T-end interval (Tpe) was shorter in patients compared to controls (p < 0.01). ECG parameters were similar between patients on and off psychopharmacotherapies aside from off-drug patients showing lower HR (56 vs. 65, p = 0.04).

CONCLUSIONS

Autonomic and repolarization changes are evident on the ECG of anorexia nervosa patients, though the QTc interval was in fact similar between groups. Changes in T-wave morphology and duration may be promising metrics of repolarization effects of anorexia nervosa.

QTc dispersion and Cornell duration product can predict 10-year outcomes in hypertensive patients with left ventricular hypertrophy

BACKGROUND

Persistent and adequate treatment of patients with arterial hypertension leads to more favorable disease outcome.

HYPOTHESIS

Aside for the present left ventricular hypertrophy (LVH), there are other non-invasive parameters which can represent additional predictors of unfavorable prognosis in patients with essential arterial hypertension during the 10-year follow-up.

METHODS

A hypertensive group with LVH (124 patients; age 57.0 ± 8.0; 84 males and 40 females) was included in the study and examined noninvasively. Patients used regular medication therapy during the follow-up period.

RESULTS

During the 10-year follow-up period, unfavorable outcome was recorded for 40 (32.3%) patients. Patients with unfavorable outcome had higher baseline values of left ventricular mass index (178.9 ± 29.5 g/m² vs 165.5 ± 29.5 g/m² ; P < 0.05) and QTc dispersion (64.1 ± 24.7 ms vs 54.8 ± 19.4 ms; P < 0.05). Frequency of positive Cornell product was higher in the group of patients with unfavorable outcome (35% vs 22.2%; P < 0.01). Positive Lyon-Sokolow score did not show statistical significance (25% vs 11.9%; P = 0.06). Cornell product (β = 0.234; P < 0.01) and QTc dispersion >65 ms (β = 0.184; P < 0.05) had prognostic significance in LVH (multiple regression analysis: R = 0.314, R = 0.099, adjusted R = 0.084, standard error of the estimate = 0.449, P < 0.05).

CONCLUSIONS

Patients with a positive Cornell product and larger QTc dispersion had more unfavorable 10-year outcomes compared with other patients with LVH.

Utility of T-wave amplitude as a non-invasive risk marker of sudden cardiac death in hypertrophic cardiomyopathy

Objective

Sudden cardiac arrest (SCA) is the most devastating outcome in hypertrophic cardiomyopathy (HCM). We evaluated repolarisation features on the surface electrocardiogram (ECG) to identify the potential risk factors for SCA.

Methods

Data was collected from 52 patients with HCM who underwent implantable cardioverter defibrillator (ICD) implantation. Leads V2 and V5 from the ECG closest to the time of ICD implant were utilised for measuring the Tpeak-Tend interval (Tpe), QTc, Tpe/QTc, T-wave duration and T-wave amplitude. The presence of the five traditional SCA-associated risk factors was assessed, as well as the HCM risk-SCD score.

Results

16 (30%) patients experienced aborted cardiac arrest over 8.5±4.1 years, with 9 receiving an ICD shock and 7 receiving ATP. On univariate analysis, T-wave amplitude was associated with appropriate ICD therapy (HR per 0.1 mV 0.79, 95% CI 0.56 to 0.96, p=0.02). Aborted SCA was not associated with a greater mean QTc duration, Tpeak-Tend interval, T-wave duration, or Tpe/QT ratio. Multivariate analysis (adjusting for cardinal HCM SCA-risk factors) showed T-wave amplitude in Lead V2 was an independent predictor of risk (adjusted HR per 0.1 mV 0.74, 95% CI 0.57 to 0.97, p=0.03). Addition of T-wave amplitude in Lead V2 to the traditional risk factors resulted in significant improvement in risk stratification (C-statistic from 0.65 to 0.75) but did not improve the performance of the HCM SCD-risk score.

Conclusions

T-wave amplitude is a novel marker of SCA in this high risk HCM population and may provide incremental predictive value to established risk factors. Further work is needed to define the role of repolarisation abnormalities in predicting SCA in HCM.

Cardiac repolarization and autonomic regulation during short-term cold exposure in hypertensive men: an experimental study

OBJECTIVES

The aim of our study was to assess the effect of short-term cold exposure, typical in subarctic climate, on cardiac electrical function among untreated middle-aged hypertensive men.

METHODS

We conducted a population-based recruitment of 51 hypertensive men and a control group of 32 men without hypertension (age 55-65 years) who underwent whole-body cold exposure (15 min exposure to temperature -10°C, wind 3 m/s, winter clothes). Conduction times and amplitudes, vectorcardiography, arrhythmias, and heart rate variability (autonomic nervous function) were assessed.

RESULTS

Short-term cold exposure increased T-peak to T-end interval from 67 to 72 ms (p<0.001) and 71 to 75 ms (p<0.001) and T-wave amplitude from 0.12 to 0.14 mV (p<0.001) and from 0.17 to 0.21 mV (p<0.001), while QTc interval was shortened from 408 to 398 ms (p<0.001) and from 410 to 401 ms (p<0.001) among hypertensive men and controls, respectively. Cold exposure increased both low (from 390 to 630 ms2 (p<0.001) and 380 to 700 ms2 (p<0.001), respectively) and high frequency heart rate variability (from 90 to 190 ms2 (p<0.001) and 150 to 300 ms2 (p<0.001), respectively), while low-to-high frequency-ratio was reduced. In addition, the frequency of ventricular ectopic beats increased slightly during cold exposure. The cold induced changes were similar between untreated hypertensive men and controls.

CONCLUSIONS

Short-term cold exposure with moderate facial and mild whole body cooling resulted in prolongation of T-peak to T-end interval and higher T-wave amplitude while QTc interval was shortened. These changes of ventricular repolarization may have resulted from altered cardiac autonomic regulation and were unaffected by untreated hypertension.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02007031.

Standard 12-lead electrocardiography measures predictive of increased appropriate therapy in implantable cardioverter defibrillator recipients

AIMS

Identification of patients most likely to benefit from implantable cardioverter defibrillator (ICD) implant remains a complex challenge. This study aimed to investigate the utility of measures derived from standard 10 s 12-lead electrocardiogrphy (ECG) without complex signal processing in predicting appropriate therapy in an ICD population.

METHODS AND RESULTS

We examined 108 ICD patients for primary (n = 32) and secondary prevention (n = 76). Baseline clinical data and characteristics of QRS complex, T-wave, and heart rate from standard 12-lead ECG were examined and related to the occurrence of subsequent appropriate therapy. Over a mean follow-up of 29 ± 11 months, 44% of patients received appropriate therapy. Patients with depressed heart rate variability (HRV) (≤6.5%) were 2.68 [95% confidence interval (CI) 1.21-5.90, P = 0.015] times more likely to receive appropriate therapy than patients with HRV >6.5%. In patients with bundle branch block (BBB), large QRS dispersion of >39 ms was associated with 2.88 times risk (95% CI 1.24-6.71, P = 0.014) of experiencing appropriate therapy than those with QRS dispersion <39 ms. In patients without BBB, reduced maximum T-wave amplitude (<0.4 mV) were 3.82 times (95% CI 1.63-8.93, P = 0.002) more likely to receive appropriate therapy compared with those with maximum T-wave amplitude >0.4 mV. History of atrial arrhythmia [hazard ratio (HR) = 2.30, 95% CI 1.29-4.12, P = 0.005] and secondary prevention (HR = 2.55, 95% CI 1.14-5.71, P = 0.022) were also predictive of device therapy.

CONCLUSION

Measurements from standard 12-lead ECG were predictive of appropriate therapy in a heterogeneous ICD population. Incorporation of 12-lead ECG parameters such as these into risk stratification models may improve our ability to select patients for ICD implantation.

Short-term repeatability of electrocardiographic spatial T-wave axis and QT interval

Although ventricular repolarization abnormalities reflect arrhythmic susceptibility, few reliable tools exist to identify their presence. We investigated the repeatability of the spatial T-wave axis and QT interval from standard 12-lead electrocardiograms in 63 asymptomatic volunteers. Certified technicians used a standardized protocol to digitally record 2 electrocardiograms per participant at each of 2 visits separated by 1 to 2 weeks. Absolute paired differences within and between visits were 0.19 degrees and 0.90 degrees for the T-wave axis and 1.08 and 1.55 milliseconds for the QT interval, respectively. The intraclass correlation coefficients for the T-wave axis and QT interval were 0.87 and 0.86, respectively. The impact of repeated measurements on the precision of the QT-interval measurements was evaluated for a hypothetical clinical trial aimed at detecting a drug-induced QT prolongation. We conclude that the spatial T-wave axis is as repeatable a measure of ventricular repolarization as the QT interval.

The association of spatial T wave axis deviation with incident coronary events. The ARIC cohort

Background

Although current evidence suggests that the spatial T wave axis captures important information about ventricular repolarization abnormalities, there are only a few and discordant epidemiologic studies addressing the ability of the spatial T wave axis to predict coronary heart disease (CHD) occurrence.

Methods

This prospective study analyzed data from 12,256 middle-aged African American and white men and women, from the Atherosclerosis Risk in Communities Study (ARIC). Following a standardized protocol, resting standard 12-lead, 10-second electrocardiograms were digitized and analyzed with the Marquette GE program. The median follow-up time was 12.1 years; incident coronary heart disease comprised fatal and non-fatal CHD events.

Results

The incidence rate of CHD was 4.26, 4.18, 4.28 and 5.62 per 1000 person-years respectively, across the spatial T wave axis quartiles. Among women for every 10 degrees increase in the spatial T wave axis deviation, there was an estimated increase in the risk of CHD of 1.16 (95% CI 1.04–1.28). After adjustment for age, height, weight, smoking, hypertension, diabetes, QRS axis and minor T wave abnormalities, this hazard rate ratio for women fell to 1.03 (0.92–1.14). The corresponding crude and adjusted hazard ratios for men were 1.05 (95% CI 0.96–1.15) and 0.95 (0.86–1.04) respectively.

Conclusions

In conclusion, this prospective, population-based, bi-ethnic study of men and women free of coronary heart disease at baseline shows that spatial T wave axis deviation is not associated with incident coronary events during long-term follow up. It is doubtful that spatial T wave axis deviation would add benefit in the prediction of CHD events above and beyond the current traditional risk factors.

T vector and loop characteristics in coronary artery disease and during acute ischemia

OBJECTIVE

Three-dimensional characterization of the ventricular repolarization by the T vector and T vector loop morphology in coronary artery disease (CAD), and their response to short-term (no flow) ischemia induced by coronary occlusion during a percutaneous intervention (PCI).

BACKGROUND

The risk for sudden cardiac death is increased in conditions of acute or permanently heterogeneous ventricular repolarization, for which ischemia is a risk factor.

METHODS

Fifty-six CAD patients without visible collateral circulation were studied during an elective single-vessel PCI, and 10 healthy controls twice at rest. T vector parameters (Televation, Tazimuth, and QRS-T angle), and T loop parameters (Tarea, Tavplan, and Teigenv) were measured by vectorcardiography. ST vector magnitude (ST-VM) and its change (STC-VM) were used for reference.

RESULTS

At rest, T vector loop morphology (Tarea, Teigenv) was significantly different in CAD patients and controls, while T vector angles did not separate the groups. Ischemia induced significant changes in T loop parameters in the entire CAD group, whereas in the LAD subgroup significant changes were seen also in T vector angle. The T loop morphology was significantly different at baseline and a more pronounced response to ischemia (Tarea) was seen in patients with, than in those without, a history of hypertension.

CONCLUSION

T loop morphology, rather than the T vector angle, separated CAD patients from healthy controls. Coronary occlusion had significant impact on ventricular repolarization, as assessed by T vector and morphology analysis, and most prominently in the LAD group. Hypertensive patients appeared especially vulnerable to ischemia.

Heart rate-dependent electrocardiogram abnormalities in patients with postural tachycardia syndrome

We recently published data suggesting the presence of an intrinsic sinus node abnormality in a subgroup of patients with the postural tachycardia syndrome (POTS). Based on the hypothesis that more widespread abnormalities of cardiac electrophysiologic properties may be present in POTS, we undertook a study to compare cardiac conduction and repolarization at different heart rate levels in patients with POTS and healthy controls. Eleven healthy controls and fourteen patients with POTS participated in the study. Acquisition of 12-lead electrocardiogram recordings were made during supine rest and during gradual head-up tilt. The heart rate of controls was titrated by isoproterenol infusion to match the heart rate of patients. Indices for cardiac conduction (PR interval, QRS duration, and R wave axis) and repolarization (QT interval, QTc interval, and T wave axis) were then compared at different heart rate levels. The PR interval decreased with increasing heart rate in controls more than in patients, resulting in a significantly longer PR interval in patients at the fastest heart rate level. The QT and QTc intervals were significantly shorter in POTS over the entire analyzed heart rate range. The T wave axis decreased with increasing heart rate in patients only. This resulted in a significantly lower T wave axis in patients at the fastest heart rate level. Our data suggest abnormalities of atrioventricular conduction and ventricular repolarization in patients with POTS. These findings may reflect intrinsic cardiac electrophysiologic abnormalities or may be secondary due to abnormalities of cardiac autonomic innervation.

The effects of cigarette smoking on the heterogeneity of ventricular repolarization

BACKGROUND

Although the circulatory effects of cigarette smoking have been studied extensively, its impact on ventricular repolarization has not been adequately evaluated.

METHODS

The goal of our study was to determine whether cigarette smoking influences the spatial and temporal heterogeneity of ventricular repolarization in a population of young, healthy, male subjects. A digital 12-lead surface electrocardiogram was obtained from 1394 men recruited from the Hellenic Air Force and classified as smokers and nonsmokers. The maximum, minimum, and median QT intervals, QT dispersion (QT maximum - QT minimum), the rate-corrected maximum and median QT intervals, the slopes of the QT maximum/RR and QT median/RR regression equations, and the vectorcardiographic markers spatial T amplitude and spatial QRS-T angle were evaluated in the 2 groups.

RESULTS

Heart rate was significantly higher (P <.001) in smokers (n =691) compared with nonsmokers (n = 703). QT maximum, QT minimum, and QT median were significantly lower (P <.001), whereas the rate-corrected QT maximum (P =.04) and QT median (P =.06) were marginally higher in smokers than in nonsmokers. The spatial T amplitude was lower (P =.002), whereas the spatial QRS-T angle was higher (P =.01) in smokers compared with nonsmokers. Neither QT dispersion nor the slopes of the QT/RR and the spatial descriptors/RR regression equations differed between smokers and nonsmokers.

CONCLUSIONS

Ventricular repolarization is altered in young male cigarette smokers. The differences in the heterogeneity of ventricular repolarization between smokers and nonsmokers are mainly due to heart rate differences between the 2 study groups.