QT interval prolongation and mortality in type 1 diabetic patients: a 5-year cohort prospective study. Neuropathy Study Group of the Italian Society of the Study of Diabetes, Piemonte Affiliate

OBJECTIVE: The aim of the study was to assess the relationship between QT interval prolongation and mortality in type 1 diabetic patients. RESEARCH DESIGN AND METHODS: Data on survival after 5 years were obtained from 316 of 379 patients (83.3%) who took part in a study on the prevalence of diabetic neuropathy and QT interval prolongation. RESULTS: Mortality at 5 years was 6.32%. Patients who survived were significantly younger (P = 0.04), had a shorter duration of diabetes (P = 0.01), had lower systolic (P = 0.004) and diastolic (P = 0.03) blood pressure levels, and had a shorter QT interval corrected for the previous cardiac cycle length (QTc) (P = 0.000005) than subjects who died. In univariate analysis, patients had a higher risk of dying if they had a prolonged QTc (odds ratio [OR] 20.14 [95% CI 5.7-70.81) or if they were affected by autonomic neuropathy (3.55 [1.4-8.9]). QTc prolongation was the only variable that showed a significant mortality OR in multivariate analysis (24.6 [6.51-92.85]; P = 0.0000004). CONCLUSIONS: This is the first cohort-based prospective study indicating that QTc prolongation is predictive of increased mortality in type 1 diabetic patients.     

Corrected QT interval in relation to the severity of diabetic autonomic neuropathy

The aim of this study was to investigate to what extent the existence of objective signs of diabetic autonomic neuropathy affects the corrected QT interval (QTc) in diabetic subjects. A total of 105 diabetic subjects (type 1, n  = 53; type 2, n  = 52) as well as 40 matched (by age and sex) control subjects were studied. All subjects underwent the battery of five Ewing tests. Autonomic neuropathy was diagnosed if two of the five tests were abnormal. In addition, the result of each test was considered as normal (grade = 0), borderline (grade = 1) or abnormal (grade = 2), and on the basis of the sum of the scores we calculated a total score for autonomic neuropathy. The QTc interval was measured at rest, and a value > 440 ms was considered abnormal. The QTc interval was significantly more prolonged in diabetic persons with autonomic neuropathy than in those without neutopathy and in control subjects: 408.4 ± 24.2 ms vs. 394.6 ± 27.9 ms and 393.6 ± 25.5 ms respectively ( P  = 0.001). Furthermore, multivariate analysis controlling for age, sex, systolic and diastolic blood pressure, body mass index (BMI), waist–hip ratio (WHR), smoking, type and duration of diabetes, type of treatment, HBA_1c and total score of autonomic neuropathy eliminated the role of all these factors as potential confounders except for the total score of autonomic neuropathy, which was found to affect QTc interval independently and significantly ( P  = 0.012). In summary, the present study confirmed the well-known relation between autonomic neuropathy and QTc interval; in addition, it showed that QTc prolongation is associated with major degrees of autonomic neuropathy.     

QTc interval prolongation is independently associated with severe hypoglycemic attacks in type 1 diabetes from the EURODIAB IDDM complications study

OBJECTIVE

Our aim was to assess whether severe hypoglycemic attacks were cross-sectionally associated with abnormalities of the QTc interval in type 1 diabetic patients.

RESEARCH DESIGN AND METHODS

The study included 3,248 type 1 diabetic patients from the EURODIAB IDDM Complications Study. Severe hypoglycemia was defined as an attack serious enough to require the help of another person. A corrected QTc interval (QTc) >0.44 s was considered abnormally prolonged.

RESULTS

Nineteen percent of patients declared one to two attacks, and 13.2% of patients had three or more attacks. Prevalence of QTc prolongation was greater in patients who experienced three or more hypoglycemic attacks. Logistic regression analysis showed that the frequency of severe hypoglycemia was independently associated with QTc prolongation, even after adjustment for diabetes complications, including autonomic neuropathy (odds ratio 1.27, 95% CI 1.02–1.58).

CONCLUSIONS

We have provided evidence that severe hypoglycemic attacks are independently associated with a prolonged QTc interval in type 1 diabetic patients from the EURODIAB IDDM Complications Study.Intensive glucose control increases the risk of severe hypoglycemia, and in the Diabetes Control and Complications Trial severe hypoglycemic episodes requiring assistance affected approximately one third of the intensively treated patients (1). Prolonged corrected QTc interval (QTc) reflects abnormalities of ventricular myocardial repolarization and is an independent marker of increased mortality in patients with type 1 diabetes (2). Physiologic and clinical studies have shown that provoked and spontaneous hypoglycemia induces QT lengthening (3,4). In the EURODIAB cohort, hypoglycemia was independently associated with autonomic neuropathy (5), which is common in patients with type 1 diabetes with prolonged QTc (6); however, the relationship between hypoglycemia and QTc prolongation was not explored. The aim of the current study was to assess whether severe hypoglycemic attacks were cross-sectionally associated with QTc abnormalities in this cohort.     

Prevalence of QTc Prolongation in Patients With Advanced Cancer Receiving Palliative Care—A Cause for Concern?

ContextMedications commonly used for symptom control along with other known risk factors have the potential to prolong ventricular repolarization as measured by the QT interval (the time from the start of the Q wave to the end of the T wave) on a standard electrocardiogram (ECG).ObjectivesTo document the prevalence of a prolonged QT interval corrected for heart rate (QTc) interval in the palliative/oncology setting, compare automatic ECG QTc measurements with manual readings and identify any correlation between QTc prolongation and the use of drugs or other risk factors.MethodsA convenience sample of consecutive patients with cancer, admitted under or known to the palliative/supportive care teams in two metropolitan hospitals, and willing to provide an ECG recording and basic demographic information including QTc risk factors were included. Both automated and manually calculated QTc intervals were recorded. Multivariable analysis was used to determine risk factors independently associated with prolonged QTc intervals.ResultsOf the 389 participants, there was a significant difference in mean QTc between sites using automated but not manual calculations. Manual readings were therefore used with predetermined cutoffs of 0.44 seconds (males) and 0.46 seconds (females). Seventy-two (18.5%) of the participants had a prolonged QTc with six (1.5%) having a prolongation of >0.50 seconds. At-risk drugs were being taken by 218 participants (56.0% of total cohort). Factors shown to be associated with QTc prolongation included age, gender, performance status, and hypocalcemia. No specific medication was associated with increased risk.ConclusionAlthough almost 20% of patients receiving palliative care had prolongation of QTc, the possibility of serious consequences appeared to be low despite the frequent occurrence of risk factors.     

Measurement of QTc in patients receiving chronic methadone therapy

Recent reports suggest that methadone may prolong the QTc interval and cause torsades de pointes. This study was conducted to evaluate the prevalence of QTc prolongation during oral methadone therapy and identify factors associated with prolongation. Patients receiving oral methadone as treatment for chronic pain or addiction were eligible for the study. One hundred four patients who were receiving > or = 20 mg methadone per day for > or = 2 weeks underwent electrocardiograms to measure QTc interval duration. Sixty-three (61%) patients were male and 63 (61%) were receiving methadone maintenance for opioid addiction. The mean (+/- SD) age was 45.3 +/- 9.4 years. The median (range) methadone dose was 110 mg/day (20-1200 mg/day); median (range) number of months on methadone was 12.5 months (1-444 months). The median (range) QTc interval was 428 msec (396-494 msec). Thirty-three percent had QTc prolongation (males 40%, females 20%; P=0.03). No patient had a QTc longer than 500 msec. Significant dose response was observed in males on methadone <12 months (rho=0.60, P=0.02). Our study suggests that methadone may prolong the QTc interval in specific subpopulations but poses little risk of serious prolongation.     

Corrected Q-T interval prolongation as diagnostic tool for assessment of cardiac autonomic neuropathy in diabetes mellitus

A simple method for evaluating alterations in cardiac sympathetic innervation may be measurement of the Q-T interval. Seventy-three diabetic patients (46 insulin dependent and 27 non-insulin dependent) were separated into four groups based on the presence and degree of cardiac autonomic neuropathy (CAN) with noninvasive cardiovascular reflexes and blood pressure responses. None of the patients had evidence of ischemic heart disease, kidney disease, or the idiopathic long Q-T-interval syndrome. The corrected Q-T interval (Q-Tc) was determined at rest with Bazett's formula. As a group, diabetic patients with greater than or equal to 2 abnormalities of cardiac autonomic function had a longer Q-Tc interval than those with no evidence of CAN. Diabetic patients with greater than or equal to 1 abnormality had a prolonged Q-Tc interval compared with a control group of 96 healthy nondiabetic subjects (mean +/- SD 397 +/- 18). The frequency of prolonged (greater than 433 ms, normal mean + 2SD) resting Q-Tc intervals increased with the increasing number of abnormalities (0, 1, 2, greater than or equal to 3): 11, 25, 41, and 75%, respectively. Twenty-three of 25 (92%) patients with a Q-Tc greater than 433 ms had evidence of CAN. However, 57% (31 of 54) of the patients with CAN had a normal Q-Tc interval. These data provide further evidence of a relationship between the presence and severity of CAN and degree of Q-Tc interval prolongation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Corrected QT-interval prolongation and variability in intensive care patients

Purpose

Critically ill patients are at risk for prolongation of the interval between the Q wave and the T wave in the electrocardiogram (corrected QT [QTc]). Corrected QT prolongation is probably a dynamic process. It is unknown how many patients have a QTc prolongation during their intensive care stay and how variable QTc prolongation is.

Materials and Methods

In a prospective cohort study, continuous 5-minute QTc measurements of 50 consecutive patients were collected. A prolonged QTc interval was more than 500 milliseconds for at least 15 minutes. The QT variance and variability index was used to evaluate QTc variation.

Results

Fifty-two percent of included patients had a prolonged QTc interval. In a single patient, 0.2% to 91.3% of the QTc intervals over time were prolonged. The use of erythromycin and amiodarone was associated with the mean QTc (P = .02 and P = .006, respectively). The Acute Physiology and Chronic Health Evaluation IV and Sequential Organ Failure Assessment scores were significantly higher in patients with a prolonged QTc interval (30.8 vs 8.6 and 7 vs 5.5, respectively). Eighty-four percent of all patients received at least 1 QTc-prolonging drug. The QT variance and QTc variance were significantly higher in patients with a prolonged QTc (P = .019 and P = .001, respectively).

Conclusion

Continuous QTc monitoring showed a prolonged QTc interval in 52% of intensive care patients. Severity of illness and QT and QTc variances are higher in these patients.     

Effects of adrenaline and potassium on QTc interval and QT dispersion in man

BACKGROUND: Hypoglycaemia alters cardiac repolarization acutely, with increases in rate-corrected QT (QTc) interval and QT dispersion (QTd) on the electrocardiogram (ECG); such changes are related to the counterregulatory sympatho-adrenal response. Adrenaline produces both QTc lengthening and a fall in plasma potassium (K+) when infused into healthy volunteers. Hypokalaemia prolongs cardiac repolarization independently however, and therefore our aim was to determine whether adrenaline-induced repolarization changes are mediated directly or through lowered plasma K+. MATERIALS AND METHODS: Ten healthy males were studied on two occasions. At both visits they received similar l-adrenaline infusions but on one occasion potassium was also administered; infusion rates were adjusted to maintain circulating K+ at baseline. The QTc interval, QTd, peripheral physiological responses and plasma adrenaline and potassium concentrations were measured during both visits. RESULTS: The QTc interval and QTd increased both with and without potassium clamping. Without K+ replacement, mean (SE) QTc lengthened from 378 (5) ms to a final maximum value of 433 (10) ms, and QTd increased from 36 (5) ms to 69 (8) ms (both P < 0.001). During K+ replacement, QTc duration at baseline and study end was 385 (7) ms and 423 (11) ms, respectively (P < 0.001), and QTd 38 was (4) ms and 63 (5) ms (P = 0.001). CONCLUSIONS: These data suggest that disturbed cardiac repolarization as a result of increases in circulating adrenaline occurs independently of extracellular potassium. A direct effect of adrenaline upon the myocardium appears the most likely mechanism.     

The C-allele of tissue inhibitor of metalloproteinases 2 is associated with increased magnitude of QT dispersion prolongation in elderly Chinese - 4-year follow-up study

BACKGROUND: Matrix metalloproteinases (MMP) and tissue inhibitor of metalloproteinases (TIMP) trigger the signal cascade instigating cardiac remodeling and fibrosis, which lead to changes of repolarization variables. We investigate the influence of MMP9-1562 C/T and TIMP2-418 G/C gene polymorphisms on repolarization parameters including QT dispersion (QTd) and the peak and the end of the T wave interval (Tpe) in a prospective cohort. METHODS: Of 1500 people screened, 106 elderly Chinese without organic heart disease were recruited and received electrocardiography at the baseline, second and 4th year follow-ups. The QTc (corrected QT), QTd, QTc dispersion (QTcd) and Tpe were manually calculated. RESULTS: Age was 72.7+/-4.1 y (range 62-81 y). QTd, QTcd and Tpe were significantly prolonged (all p <0.001 at the 2nd and 4th year). At the 4th year the magnitude of QTd prolongation but not Tpe was significantly higher in subjects carrying the TIMP2 C-allele than non C-allele carriers (p=0.033) as well as QTcd (p=0.010). This association was still significant in multivariate analyses (p=0.012 and p=0.003 for QTd and QTcd, respectively) but not in MMP9 genotype. CONCLUSIONS: The elderly Chinese with TIMP2 C-allele have higher magnitude of QTd and QTcd prolongation.     

Assessment of corrected QT interval in sickle-cell disease patients who undergo erythroapheresis

Extension of the QT interval is characterized by syncope and cardiac arrest and often occurs in association with medical therapies and procedures. Whether erythroapheresis (EPH) could influence the QT interval duration in patients with sickle cell disease (SCD) is not known. We aimed to investigate the effects of EPH on the heart rate-corrected QT (QTc) interval. The study included 25 patients with SCD who underwent 34 EPH procedures. Two independent observers measured QTc interval duration from electrocardiograms performed continuously for 3 min at three different points during the EPH procedures (prior to EPH, after completion of 50% EPH and 15 min after EPH). Multiple regression analysis was used to determine if the ionized plasma calcium, the level of plasma magnesium, citrate infusion rate and painful crisis significantly contributed to the QTc interval. There was a non-significant trend (P = 0.184) towards increased QTc in sickle cell patients during EPH compared with pre-EPH values. QTc prolongation (>440 ms) occurred in 72% of the procedures. Fifty percent QTc values returned to baseline after the procedure. The independent variables were not significantly associated with QTc interval. Exchange procedures can induce QTc prolongation in patients with SCD.     

Reassessing the role of QTc in the diagnosis of autonomic failure among patients with diabetes: a meta-analysis

OBJECTIVE: A 1992 consensus statement on autonomic testing portrayed Bazett's heart rate-corrected QT interval (QT) prolongation as a specific yet insensitive indicator of diabetic autonomic failure. At that time, only a few small studies had evaluated the accuracy of QTc. To date, even fewer studies have evaluated whether its accuracy is influenced by patient characteristics. RESEARCH DESIGN AND METHODS: We critically appraised 17 studies reporting the sensitivity and specificity of QTc for diabetic autonomic failure. The studies represented 4,584 patients with diabetes (mean age 34.9 years, 46% female, 92% with type 1 diabetes, mean duration of diabetes 14.5 years). We summarized the accuracy of QTc prolongation for diabetic autonomic failure as an odds ratio (OR) (95% CI) and determined whether patient and study design characteristics influenced the accuracy of QTc prolongation by comparing summary receiver operating characteristic curves. RESULTS: Autonomic failure, defined as > or =1.2+/-0.4 (mean +/- SD) abnormal of 2.0+/-1.6 administered cardiovascular reflex tests, was found in 26% (25-28) of patients. The pooled sensitivity and specificity of QTc > 441+/-8 ms for autonomic failure were 28% (26-29) and 86% (85-87), respectively. Autonomic failure was 2.26 times (1.90-2.70) more likely to be present in patients with than in patients without QTc prolongation. At 86% specificity, the sensitivity of QTc prolongation was 46 vs. 12% for men versus women (P = 0.0077), respectively, and, after adjustment for sex, 66 vs. 17% among patients aged 25 vs. 55 years (P = 0.1902) and 61 vs. 27% at thresholds of >420 vs. >460 ms, respectively (P = 0.2964). CONCLUSIONS: QTc prolongation is a specific albeit insensitive indicator of autonomic failure. Although QTc prolongation is relatively accurate for men, accuracy may be even greater for young men at low QTc thresholds.     

食管心房超速负荷试验中QT间期离散度变化对冠心病的诊断价值

目的探讨食管心房超速负荷试验的QT间期离散度 (QTd)对冠心病的诊断价值。方法对冠脉造影确诊为冠心病 38例及冠脉造影正常 4 0例进行食管心房超速负荷试验 ,记录试验前后 12导联心电图 ,测量ST段 ,校正QTc及QTd ,利用四格表法 ,分别计算各指标的特异性及敏感性。结果冠心病组试验后QTc及QTd均较试验前明显延长 (P<0 .0 1) ,试验后冠心病组QTd也长于非冠心病组 (P <0 .0 5 )。ST段 ,QTc及QTd诊断冠心病的特异性分别为 95 % ,6 7.5 % ,87.5 % ,敏感性分别为 5 2 .6 % ,73.7% ,84 .2 %。结论食管心房超速负荷试验的QT间期离散度 (QTd)能增加冠心病的诊断敏感度 ,对冠心病具有较高的诊断价值。     

艾司西酞普兰对抑郁症患者QTc间期的影响

目的 探讨艾司西酞普兰对抑郁症患者QTc间期的影响.方法 将58例抑郁症患者随机分为两组,观察组口服艾司西酞普兰治疗,对照组口服帕罗西汀治疗.观察4周.治疗前后检测两组电解质及心电图的变化.结果 治疗前后两组电解质各项指标均无显著变化（P＞0.05）,QTc间期虽较治疗前有所延长,但差异均无显著性（P＞0.05）;同期两组QTc间期及治疗后QTc间期延长值比较差异均无显著性（P＞0.05）.结论 常规剂量艾司西酞普兰治疗对抑郁症患者QTc间期无明显影响.     

Pharmacokinetics and pharmacodynamics of esmolol administered as an intravenous bolus

Esmolol is a new ultra-short-acting beta-adrenergic receptor blocking agent that may be useful in the treatment of patients with heart disease. We gave esmolol as an intravenous bolus injection (over 30 seconds) to 12 healthy men in a dose-ranging study; each subject received two doses. Our dosing schedule began with 30 mg in the first subject and ended with 100 mg and 150 mg in the final four subjects. We measured blood esmolol concentration, PR interval, QRS duration, QTc interval, cardiac cycle, systolic blood pressure, and diastolic blood pressure. Esmolol doses of 150 mg produced blood esmolol concentrations of 0.868 to 1.47 micrograms/ml. The peak PR interval recorded after esmolol was significantly longer than the control PR interval in four subjects who received 100 and 150 mg doses (192 +/- 7.9 msec vs. 177 +/- 10.6 msec; P = 0.00002). Peak prolongation of the PR interval was recorded 6 to 10 minutes after the bolus, at which time blood esmolol concentrations were negligible. Esmolol did not consistently affect any other pharmacodynamic variable. Giving esmolol as an intravenous bolus injection may be a simple alternative to loading and maintenance infusion in some clinical settings.     

Is there a relationship between the blood cholinesterase and QTc interval in the patients with acute organophosphate poisoning?

Organophosphates cause poisoning as a result of the excessive accumulation of acetylcholine at the cholinergic synapses due to inhibition of acetylcholinesterase (ChE). In the literature, it has been reported that there have been electrocardiographic abnormalities, including QT-interval prolongation in most patients with acute organophosphate poisoning (OPP), and a relation between blood ChE level and clinical severity in acute OPP. The aim of this study is to assess the relationship between blood ChE level and QTc interval in the patients with acute OPP. This retrospective study consists of 20 patients admitted to the emergency intensive care unit. A total of 93 QTc interval and blood ChE measures obtained on the same day from 20 cases were compared for their correlation. There were prolonged QTc intervals in 35.4% of the ECGs. There was a negative correlation between QTc interval and blood ChE measures. In following up the patients with acute OPP, QTc interval may be useful when blood ChE levels are low and may provide complementary information concerning the severity of poisoning. However, further prospective studies, supporting the present results, are needed.     

急性有机磷农药中毒患者心电图的改变

目的 探讨急性有机磷农药中毒(AOPP)患者的心电图变化,重点阐述AOPP患者的QTc间期长短与血浆胆碱酯酶浓度(ChE)的关系.方法 回顾分析2006-01～2008-06期间入住我院的32例AOPP患者.收集患者入院2h内的心电图和血浆ChE检查结果,并对心电图QTc间期和血浆ChE进行相关性分析.结果 患者年龄为(37.6±18.6)岁,女性患者23例(71.8%).QTc间期的平均长度为(441.2±22.5)ms.QTc间期延长12例(37.5%),是最常见的心电图的异常变化;其次是非特舁性ST-T改变7例(21.8%),窦性心动过速6例(18.8%),P-R间期缩短4例(12.5%),期前收缩5例(15.6%),窦性心动过缓2例(6.25%).QTc间期长短和血浆ChE呈负相关(r=-0.419,P<0.05).结论 AOPP患者常见的心电图变化包括:QTc间期延长、非特异性ST-T改变和心律失常.QTc间期长短和血浆胆碱酯酶浓度呈负相关.由此推测,AOPP患者的QTc间期的长短对判断患者的中毒程度有一定的意义.     

四硫化四砷对急性早幼粒细胞白血病患者心电图QTc问期的影响

目的探讨四硫化四砷(As4S4)对急性早幼粒细胞白血病(APL)患者心电图校正后QT(QTc)间期的影响.方法复方柏子仁(主要成分As4S4)治疗的90例患者分为诱导缓解组和巩固维持治疗组.诱导缓解组测定并记录患者服药前及缓解后的血砷浓度及同步12导联心电图;巩固维持治疗组测定并记录患者服药前及第2,4,6,8,10疗程后的血砷浓度及心电图.测量每份心电图的QT间期值,以Bazett公式校正,计算出QTc,观察血砷浓度与QTc间期的关系.结果无论诱导缓解组还是巩固维持治疗组,口服As4S4均能引起QTc间期的延长,QTc与As4S4的剂量及血砷浓度有关,随着As4S4的累积剂量或血砷浓度增大,QTc值及其延长的幅度也增大.在巩固维持治疗组服药的10个疗程中,QTc值异常(≥440 ms)率平均为 37.7%,随服用As4S4累积剂量的增加,各疗程血砷浓度缓慢上升,但各疗程之间的变化差异无显著性(P>0.05).各疗程中QTc间期虽逐步延长,但QTc值异常率在各疗程中无显著性差异(P>0.05).QTc异常的患者均无临床症状,未出现室性心动过速或尖端扭转型室性心动过速等病变,无一例患者因QTc间期延长而终止治疗.结论 As4S4治疗APL虽可引起QTc间期延长,且QTc间期的变化与血砷浓度呈正相关,但As4S4仍为一种安全的治疗APL的药物.     

Heart block and prolonged Q-Tc interval following muscle relaxant reversal: a case report

Heart block and Q-Tc interval prolongation have been reported with several agents used in anesthesia, and the US Food and Drug Administration mandates evaluation of the Q-T interval with new drugs. Drug-induced Q-T interval prolongation may precipitate life-threatening arrhythmias, is considered a precursor for torsades de pointes, and may predict cardiovascular complications. In the patient described in this article, heart block occurred and the Q-Tc interval became prolonged after muscle relaxant reversal with neostigmine; both were considered to be related to the combination of agents used in the case, as well as to other predisposing factors such as morbid obesity. The agents used that affected cardiac conduction were neostigmine, desflurane, droperidol, dolasetron, and dexmedetomidine. Although the heart block was resolved after 2 doses of atropine, prolonged P-R and Q-Tc intervals persisted into the immediate postoperative period but returned to baseline within 4 hours. Clinical implications of this report include increasing awareness of the multitude of factors affecting Q-T interval prolongation during anesthesia.     

Modulation of the Q-T Interval by the Autonomic Nervous System

Recent investigations have clarified some of the effects of the autonomic nervous system on duration and spatial distribution of the Q-T interval in humans. The use of atrial pacing to fix heart rate or 24-hour continuous electrocardiographic recording to develop a regression formula for individual patients has provided a means to interpret the effects of an intervention that alters both the heart rate and the Q-T interval. Drugs that affect Ihe autonomic nervous system can influence Q-T interval directly or by changing rate. Bazett's formula to correct for rate may be misleading after certain drug interventions. For example, the Q-T interval during sinus rhythm or afrial pacing and the ventricular effective refractory period shorten after atropine plus propranolol, but corrected Q-T interval using Bazetf's formula does not change. No change occurs in the Q-T interval during sinus rhythm or atrial pacing, or in ventricular effective refractory period after administration of propranolol although corrected Q-T interval using Bazett's formula markedly shortens. Q-T interval during sinus rhythm and atrial pacing and ventricular effective refractory period decrease after atropine but correct Q-T interval lengthens. To define further the relationship of the autonomic nervous system on the duration of the Q-T interval we studied the effects of sleep. Fifteen patients receiving no drugs underwent 3–6 days of continuous electrocardiography recordings. The duration of the Q-T interval was longer during sleep in all 15 patients independent of heart rate change. This prolongation of the Q-T interval during sleep may reflect increased parasympathetic tone or decreased sympathetic tone on the ventricle. Further investigation of the relation of the autonomic nervous system to ventricular depolarization and repolarization may delineate some of Ihe trigger mechanisms for the development of lethal ventricular arrhythmias in humans.     

Prolonged corrected QT interval in hospitalized patients with coronavirus disease 2019 in Dubai,United Arab Emirates: a single-center, retrospective study

ObjectiveTo evaluate the association of a prolonged corrected QT (QTc) interval in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and its association with in-patient mortality.MethodsA cohort of 745 patients were recruited from a single center between 1 March 2020 and 31 May 2020. We analyzed the factors associated with a prolonged QTc and mortality.ResultsA prolonged QTc interval >450 ms was found in 27% of patients admitted with SARS-CoV-2 infection. These patients were predominantly older, on a ventilator, and had hypertension, diabetes mellitus, or ischemic heart disease. They also had high troponin and D-dimer concentrations. A prolonged QTc interval had a significant association with the requirement of ventilator support and was associated with an increased odds of mortality. Patients who died were older than 55 years, and had high troponin, D-dimer, creatinine, procalcitonin, and ferritin concentrations, a high white blood cell count, and abnormal potassium concentrations (hypo- or hyperkalemia).ConclusionsA prolonged QTc interval is common in patients with SARS-CoV-2 infection and it is associated with worse outcomes. Older individuals and those with comorbidities should have an electrocardiogram performed, which is noninvasive and easily available, on admission to hospital to identify high-risk patients.