Precordial ECG Amplitudes in the Days After Birth: Electrocardiographic Changes During Transition from Fetal to Neonatal Circulation.

During the first month of life, the relation between right and left ventricular function is markedly altered. We aimed at describing the electrocardiographic transition from fetal to neonatal circulation by investigating changes in R- and S-wave amplitudes in V1 and V6 during the first 4 weeks of life. This study is part of the prospective, population-based Copenhagen Baby Heart Study offering cardiac evaluation to newborns within 28 days from birth. ECGs were obtained and analyzed using a computerized algorithm. A total of 14,577 newborns (52% boys), median age of 11.0 days, were included. All had normal echocardiograms. Within 28 days from birth, the amplitudes in V1 decreased: R-V1 (1262 µV day0; 947 µV day28, p < 0.001) and S-V1 (1240 µV day0; 473 µV day28, p < 0.001). An increase was observed for R-V6 (825 µV day0; 1196 µV day28, p = 0.002), while S-V6 decreased (830 µV day0; 634 µV day28, p = 0.003). For all amplitudes, interindividual variation was large (up to 20 times). The amplitudes were not affected by sex (p > 0.05), but R-V1, R-V6, and S-V6 positively correlated with newborn weight (p < 0.01). R-V1 and S-V6 showed positive correlation with gestational age (p < 0.05). In conclusion, systematic analyses of ECGs from healthy newborns showed significant decreases in R-V1, S-V1, and S-V6 amplitudes, while R-V6 increased. Interindividual variation was large, making ECGs unlikely as a sensitive tool for diagnosing congenital heart diseases. Our data may serve as updated, digitalized reference values in newborns.

Associations between left bundle branch block with different PR intervals, QRS durations, heart rates and the risk of heart failure: a register-based cohort study using ECG data from the primary care setting.

AIM: Left bundle branch block (LBBB) is associated with an increased risk of heart failure (HF). We assessed the impact of common ECG parameters on this association using large-scale data. METHODS AND RESULTS: Using ECGs recorded in a large primary care population from 2001 to 2011, we identified HF-naive patients with a first-time LBBB ECG. We obtained information on sex, age, emigration, medication, diseases and death from Danish registries. We investigated the association between the PR interval, QRS duration, and heart rate and the risk of HF over a 2-year follow-up period using Cox regression analysis.Of 2471 included patients with LBBB, 464 (18.8%) developed HF during follow-up. A significant interaction was found between QRS duration and heart rate (p<0.01), and the analyses were stratified on these parameters. Using a QRS duration <150 ms and a heart rate <70 beats per minute (bpm) as the reference, all groups were statistically significantly associated with the development of HF. Patients with a QRS duration ≥150 ms and heart rate ≥70 bpm had the highest risk of developing HF (HR 3.17 (95% CI 2.41 to 4.18, p<0.001). There was no association between the PR interval and HF after adjustment. CONCLUSION: Prolonged QRS duration and higher heart rate were associated with increased risk of HF among primary care patients with LBBB, while no association was observed with PR interval. Patients with LBBB with both a prolonged QRS duration (≥150 ms) and higher heart rate (≥70 bpm) have the highest risk of developing HF.

Thyroid dysfunction and electrocardiographic changes in subjects without arrhythmias: a cross-sectional study of primary healthcare subjects from Copenhagen.

OBJECTIVE: The objective of the present study was to investigate associations of both overt and subclinical thyroid dysfunction with common ECG parameters in a large primary healthcare population. DESIGN: Cross-sectional study. SETTING AND PARTICIPANTS: The study population comprised of primary healthcare patients in Copenhagen, Denmark, who had a thyroid function test and an ECG recorded within 7 days of each other between 2001 and 2011. DATA SOURCES: The Danish National Patient Registry was used to collect information regarding baseline characteristics and important comorbidities. OUTCOME MEASURE AND STUDY GROUPS: Common ECG parameters were determined using Marquette 12SL software and were compared between the study groups. The study population was divided into five groups based on their thyroid status. Euthyroid subjects served as the reference group in all analyses. RESULTS: A total of 132 707 patients (age 52±17 years; 50% female) were included. Hyperthyroidism was significantly associated with higher heart rate and prolonged QTc interval with significant interaction with age (p<0.009) and sex (p<0.001). These associations were less pronounced for patients with higher age. Subclinical hyperthyroidism was associated with higher heart rate among females, and a similar trend was observed among males. Hypothyroidism was associated with slower heart rate and shorter QTc but only in women. Moreover, longer P-wave duration, longer PR interval and low voltage were observed in patients with both subclinical and overt hypothyroidism. However, the presence of low voltage was less pronounced with higher age (p=0.001). CONCLUSION: Both overt and subclinical thyroid disorders were associated with significant changes in important ECG parameters. Age and gender have significant impact on the association of thyroid dysfunction particularly on heart rate and QTc interval.

Associations between common ECG abnormalities and out-of-hospital cardiac arrest.

Background: Out-of-hospital cardiac arrest (OHCA) is often the first manifestation of unrecognised cardiac disease. ECG abnormalities encountered in primary care settings may be warning signs of OHCA. Objective: We examined the association between common ECG abnormalities and OHCA in a primary care setting. Methods: We cross-linked individuals who had an ECG recording between 2001 and 2011 in a primary care setting with the Danish Cardiac Arrest Registry and identified OHCAs of presumed cardiac cause. Results: A total of 326 227 individuals were included and 2667 (0,8%) suffered an OHCA. In Cox regression analyses, adjusted for age and sex, the following ECG findings were strongly associated with OHCA: ST-depression without concomitant atrial fibrillation (HR 2.79; 95% CI 2.45 to 3.18), left bundle branch block (LBBB; HR 3.44; 95% CI 2.85 to 4.14) and non-specific intraventricular block (NSIB; HR 3.15; 95% CI 2.58 to 3.83). Also associated with OHCA were atrial fibrillation (HR 1.89; 95% CI 1.63 to 2.18), Q-wave (HR 1.75; 95% CI 1.57 to 1.95), Cornell and Sokolow-Lyon criteria for left ventricular hypertrophy (HR 1.56; 95% CI 1.33 to 1.82 and HR 1.27; 95% CI 1.12 to 1.45, respectively), ST-elevation (HR 1.40; 95% CI 1.09 to 1.54) and right bundle branch block (HR 1.29; 95% CI 1.09 to 1.54). The association between ST-depression and OHCA diminished with concomitant atrial fibrillation (HR 1.79; 95% CI 1.42 to 2.24, p < 0.01 for interaction). Among patients suffering from OHCA, without a known cardiac disease at the time of the cardiac arrest, 14.2 % had LBBB, NSIB or ST-depression. Conclusions: Several common ECG findings obtained from a primary care setting are associated with OHCA.