The duration of ventricular systole as measured by the Q-T interval of the electrocardiogram, with especial reference to cardiac enlargement with and without congestive failure

Golden Standard or Obsolete Method? Review of ECG Applications in Clinical and Experimental Context

Cardiovascular system and its functions under both physiological and pathophysiological conditions have been studied for centuries. One of the most important steps in the cardiovascular research was the possibility to record cardiac electrical activity. Since then, numerous modifications and improvements have been introduced; however, an electrocardiogram still represents a golden standard in this field. This paper overviews possibilities of ECG recordings in research and clinical practice, deals with advantages and disadvantages of various approaches, and summarizes possibilities of advanced data analysis. Special emphasis is given to state-of-the-art deep learning techniques intensely expanded in a wide range of clinical applications and offering promising prospects in experimental branches. Since, according to the World Health Organization, cardiovascular diseases are the main cause of death worldwide, studying electrical activity of the heart is still of high importance for both experimental and clinical cardiology.

Markedly prolonged QTc interval in end-stage liver disease and risk of 30-day cardiovascular event after liver transplant

BACKGROUND AND AIM

The proportional increase of corrected QT interval (QTc) along end-stage liver disease (ESLD) severity may lead to inconsistent outcome reporting if based on conventional threshold of prolonged QTc. We investigated the comprehensive QTc distribution among ESLD patients and assessed the association between QTc > 500 ms, a criterion for diagnosing severe long-QT syndrome, and the 30-day major adverse cardiovascular event (MACE) after liver transplantation (LT) and identified the risk factors for developing QTc > 500 ms.

METHODS

Data were collected prospectively from the Asan LT Registry between 2011 and 2018, and outcomes were retrospectively reviewed. Multivariable analysis and propensity score-weighted adjusted odds ratios (ORs) were calculated. Thirty-day MACEs were defined as the composite of cardiovascular mortality, arrhythmias, myocardial infarction, pulmonary thromboembolism, and/or stroke.

RESULTS

Of 2579 patients, 194 (7.5%) had QTc > 500 ms (QTc500_Group), and 1105 (42.8%) had prolonged QTc (QTcP_Group), defined as QTc > 470 ms for women and >450 ms for men. The 30-day MACE occurred in 336 (13%) patients. QTc500_Group showed higher 30-day MACE than did those without (20.1% vs 12.5%, P = 0.003), with corresponding adjusted OR of 1.24 (95% CI: 1.06-1.46, P = 0.007). However, QTcP_Group showed comparable 30-day MACE (13.3% vs 12.8% without prolonged QTc, P = 0.764). Significant risk factors for QTc > 500 ms development were advanced liver disease, female sex, hypokalemia, hypocalcemia, high left ventricular end-diastolic volume, and tachycardia.

CONCLUSION

Our results revealed that, among ESLD patients, a novel threshold of QTc > 500 ms was associated with post-LT 30-day MACE but not with conventional threshold, indicating that a longer QTc threshold should be considered for this unique patient population.

Acquired long QT syndrome: frequency, onset, and risk factors in intensive care patients

BACKGROUND

Acquired long QT syndrome is a reversible condition that can lead to torsades de pointes and sudden cardiac death.

OBJECTIVE

To determine the frequency, onset, frequency of medications, and risk factors for the syndrome in intensive care patients.

METHODS

In a retrospective chart review of 88 subjects, hourly corrected QT intervals calculated by using the Bazett formula were collected. Acquired long QT syndrome was defined as a corrected QT of 500 milliseconds or longer or an increase in corrected QT of 60 milliseconds or greater from baseline level. Risk factors and medications administered were collected from patients' medical records.

RESULTS

The syndrome occurred in 46 patients (52%); mean time of onset was 7.4 hours (SD, 9.4) from time of admission. Among the 88 patients, 52 (59%) received a known QTc-prolonging medication. Among the 46 with the syndrome, 23 (50%) received a known QT-prolonging medication. No other risk factor studied was significantly predictive of the syndrome.

CONCLUSIONS

Acquired long QT syndrome occurs in patients not treated with a known QT-prolonging medication, indicating the importance of frequent QT monitoring of all intensive care patients.

QT interval in cardiac amyloidosis

The aim of the study was to investigate whether cardiac amyloidosis is associated with QT interval abnormalities and ventricular arrhythmias. A controlled study of 30 patients was undertaken at a university cardiology department in a large referral hospital. Thirty patients (18 men, 12 women, mean age 56 +/- 12 years) with systemic amyloidosis verified by biopsy and strong indications of cardiac amyloidosis comprised the study group, with 30 healthy age- and sex-matched individuals serving as controls. Complete M-mode and two-dimensional echocardiographic study was undertaken and QT interval and QTc were calculated. All patients and controls underwent 24-h Holter monitoring for arrhythmias. Left ventricular (LV) wall thickening was found in all patients with cardiac amyloidosis. The LV mass in the patients with cardiac amyloidosis was significantly greater than that of the control group, as was the ratio LV mass/body surface area (p < 0.001). There was no significant difference in the max QT interval or in QTc dispersion between the two groups, although the max QTc was greater in the patients with cardiac amyloidosis. Patients with cardiac amyloidosis did not have a higher incidence of arrhythmias than the controls. Although patients with thickened cardiac walls due to cardiac amyloidosis have a prolonged QTc in comparison with controls, they do not show an increase in interlead QTc dispersion which might suggest the possibility of regional disturbances of the uniformity of repolarization. Patients with cardiac amyloidosis do not have a higher incidence of arrhythmias than controls.

Prolonged QT interval in hypertrophic and dilated cardiomyopathy in children

When the QT interval is prolonged in a patient with structural heart disease, there is a question of whether the QT interval prolongation is the result of coexistent long QT interval syndrome or ventricular hypertrophy. The purpose of this study was to assess whether QT interval prolongation can be attributed to ventricular hypertrophy/dilation alone. Electrocardiograms (ECGs) of 25 children in each of six echocardiographically proven groups (right ventricular hypertrophy, left ventricular hypertrophy, biventricular hypertrophy, hypertrophic cardiomyopathy, dilated cardiomyopathy, and normals) were analyzed. All patients had QRS interval durations < 100 msec, and patients with ventriculotomies were excluded. No patients in the normal group had a QTc interval > or = 0.45 sec. Eight (32%) of 25 patients with dilated cardiomyopathy had a QTc interval > or = 0.45 sec (p = 0.007 vs normal), 6 (24%) of 25 patients with hypertrophic cardiomyopathy had a QTc interval > or = 0.45 sec (p = 0.03 vs normal), and 2 of 25 patients each with right ventricular hypertrophy, left ventricular hypertrophy, and biventricular hypertrophy had a QTc interval > or = 0.45 sec (p = NS vs normal). There was no relation of the QTc interval to age, QRS duration, T-wave axis, or heart rate in any group. In the dilated cardiomyopathy group, there was no relationship of QTc interval to age, shortening fraction, or left ventricular end diastolic dimension. In conclusion, (1) a significant number of patients (24% to 32%) with dilated or hypertrophic cardiomyopathy may have a long QTc interval on the surface ECG, and (2) ventricular hypertrophy/dilation may be additional rare causes of acquired prolongation of the QT interval.

Left axis deviation in tricuspid atresia and single ventricle; the electrocardiogram in 36 autopsied cases

The electrocardiograms from 28 unselected autopsied cases of tricuspid atresia, and eight autopsied cases of single ventricle were analysed: only those cases of single ventricle which showed left axis deviation were included. Electrocardiographic evidence of left ventricular preponderance in the precordial and unipolar limb leads was found in 27 of the 28 cases of tricuspid atresia, and three of the eight of single ventricle: In only two cases of single ventricle was the electrocardiogram identical with that seen in tricuspid atresia, and in one of them tricuspid stenosis was present. Right auricular hypertrophy as evidenced by high peaked P waves, together with presystolic hepatic pulsations occurred in tricuspid atresia in those instances in which, at autopsy, the interauricular communication was found to be small.

Postoperative changes in the electrocardiogram in congenital heart disease. II. Coarctation of the aorta and patent ductus arteriosus

Electrocardiograms of 41 cases of coarctation and of 73 cases of patent ductus arteriosus were analyzed before and after surgical correction of the defect. The changes in the electrocardiogram which occurred after surgical repair of the coarctation were considered to be due to the diminished load on the left ventricle. In 65 of the cases of patent ductus arteriosus, electrocardiographic signs of left ventricular hypertrophy were recorded. Eight patients, seven of whom presented atypical murmurs, showed evidence of right ventricular or combined ventricular hypertrophy. Following ligation of the ductus, the electrocardiogram became normal in the majority of the cases.

The Q-T Interval in Chronic Cor Pulmonale

In 13 patients in whom the diagnosis of chronic cor pulmonale was made after careful physiologic studies, the Q-T interval was found to be within normal limits regardless of the presence or absence of cardiac failure. The finding is in sharp contrast to the prolongation of this interval in the more common types of heart disease, as exemplified by a group of 14 patients with hypertensive and arteriosclerotic heart disease. Measurement of the Q-T interval therefore may be useful in differentiating pure chronic cor pulmonale from other types of heart disease with congestive failure.

The Q-T Interval in Normal Infants and Children

Because of renewed clinical interest in the Q-T interval and because of a need of normal values for an accompanying investigation in rheumatic fever, the Q-T was studied in 517 normal infants and children from birth to 13 years of age. A mean K of 0.404 for Bazett's formula and of 0.378 for Ashman and Hull's formula was obtained. With Bazett's curve approximating the data more closely, a Bazett's scattergram of the normal Q-T at varying heart rates was constructed. Although no difference in K value was noted between the sexes, significant differences were observed in certain age groups.