Differential effect of glyburide (glibenclamide) and metformin on QT dispersion: a potential adenosine triphosphate sensitive K+ channel effect

Glyburide (glibenclamide) is a specific blocker of the adenosine triphosphate (ATP) sensitive potassium (K+) channel. It has been reported to result in prolongation of the QT interval. QT interval dispersion (QTd) is a potentially sensitive marker for increased risk of arrhythmia and sudden cardiac death. The aim of the present study was to evaluate the effect of glyburide on QTd and compare it with that of metformin, a hypoglycemic agent that does not block the adenosine triphosphate sensitive K+ channel. Thirty patients with type 2 diabetes were randomized to glyburide and metformin groups. A 12-lead electrocardiogram was obtained before and at 2 months after being on glyburide or metformin. Therapy with QT and QTd were measured and QT corrected for rate (QTc). There was no significant difference between the glyburide and metformin groups in age (62 +/- 9 vs 59 +/- 10 years), baseline RR interval (819 +/- 86 vs 753 +/- 100 ms), QT (387 +/- 28 vs 383 +/- 27 ms), and QTc (433 +/- 25 vs 444 +/- 15 ms). Glyburide was associated with a significant increase in QTc (433 +/- 24 to 467 +/- 24 ms, p <0.001), QTd (24 +/- 16 to 60 +/- 22 ms, p <0.001), and QTc dispersion (QTcd) (35 +/- 18 to 68 +/- 21 ms, p <0.001). In contrast, metformin was associated with a decrease in QTc (444 +/- 15 to 432 +/- 15 ms, p <0.01) and did not affect QTd (14 +/- 5 to 12 +/- 6 ms, p = NS) and QTcd (23 +/- 9 to 22 +/- 10 ms, p = NS). Glyburide, unlike metformin, causes an increase in QT dispersion. Increased dispersion may be a factor underlying an increased risk of arrhythmias and sudden cardiac death.     

Effects of isolated coronary artery ectasia on electrocardiographic parameters reflecting ventricular heterogeneity

Isolated coronary ectatic but otherwise normal epicardial coronary arteries are an infrequent angiographic finding. We sought to determine whether coronary artery ectasia (CAE) may alter QT-interval duration and dispersion. The study population consisted of 24 patients with isolated CAE and otherwise normal epicardial coronary arteries (group 1) and sex- and age-matched subjects with atypical chest pain and otherwise normal coronary flow (group 2). Both groups underwent a routine standard 12-lead surface electrocardiogram recorded at 50 mm/s during rest. QT dispersion (QTd), corrected QT (QTc), and corrected QT dispersion (QTcd) were calculated. Distribution of sex, age, body mass index, and cardiac risk factors were similar in the 2 groups. Mean heart rate was similar in the 2 groups (74 ± 10 vs 70 ± 7, P > .05). In group 1, QTd, QTcd, and QTc were significantly higher than those of group 2 (QTd, 40 ± 17 vs 29 ± 10 milliseconds [P < .05]; QTcd, 43 ± 19 vs 30 ± 10 milliseconds [P < .05]; QTc, 410 ± 21 vs 397 ± 19 milliseconds [P < .05]). In conclusion, CAE was found to be associated with prolonged QT interval and increased QTd. Microvascular dysfunction and/or ischemia may be responsible mechanisms.     

QT离散度对心衰患者心脏事件的预测价值

目的探讨QT离散度(QTd)、校正QT离散度(QTcd)及心率校正QT间期(QTc)对心衰患者心脏事件的预测价值。方法回顾性研究了106例充血性心力衰竭(CHF)患者QTd、QTcd、及QTc的资料。结果心脏事件发生组CHF病人(Ⅰ组)QTd、QTcd、QTc、QTcd/QTc与无心脏事件发生组(Ⅱ组)比较有显著的统计学差异(P<0.05、<0.01、<0.05、<0.001)。结论QTd、QTcd、QTc、QTcd/QTc是心衰病人心脏事件独立预测因子,QTcd/QTc准确性最高。     

急性心肌梗死恢复期PTCA及支架置入术对QT离散度的影响

目的　观察急性心肌梗死 (AMI)恢复期 (2～ 4周 )行经皮冠状动脉腔内成形术 (PTCA)及支架置入术对QT离散度 (QTd)的影响。方法　选择 5 7例AMI恢复期的患者 ,分别记录PTCA及支架置入术前 1d ,术后 1h的 12导联同步心电图 ,测量QTd及校正的QTd(QTcd) ,并与 86例同期行冠状动脉造影结果正常者进行对照。结果　AMI组行PTCA及支架置入术前最大QT间期 (QTmax) ,最小QT间期 (QTmin) ,QTd及QTcd均较对照组明显增大 ,差异有显著性。前壁与下壁AMI之间上述指标差异无显著性。成功的PTCA及支架置入术后QTmax,QTmin,QTd及QTcd比术前明显缩短 ,两者相比差异有显著性。而单纯行冠状动脉造影对QT离散度无明显影响。结论　AMI患者QTd及QTcd显著高于正常人 ,而AMI恢复期成功的PTCA及支架置入术可使增加的QTd及QTcd显著缩短 ,从而减低AMI后恶性心律失常和心源性猝死的发生率 ,改善患者的远期预后。     

D-allele of ACE polymorphism is associated with increased magnitude of QT dispersion prolongation in elderly Chinese: 4-year follow-up study.

BACKGROUND: There has not been a longitudinal investigation of the influence of angiotensin-converting enzyme (ACE) insertion/deletion and angiotensinogen (AGT) M235T gene polymorphisms on repolarization parameters, such as QT dispersion (QTd) and the peak and the end of the T-wave interval (Tpe). METHODS AND RESULTS: Electrocardiographys were recorded from 106 elderly Chinese at baseline, and 2nd and 4th year follow-up. The corrected QT (QTc), QTd, QTc dispersion (QTcd) and Tpe were manually calculated. Average age was 72.7+/-4.1 years (range 62-81). QTd, QTcd and Tpe were significantly prolonged (all p<0.001 at the 2nd and 4th year). At the 4th year the magnitude of the QTd prolongation, but not Tpe, was significantly higher in subjects carrying the ACE D allele than non-D-allele carriers (p=0.001), as was QTcd (p=0.002). This association was still significant in the multivariate analyses (p<0.001 and p=0.001 for QTc and QTcd, respectively). No significant correlation was found between repolarization parameters and AGT genotype. CONCLUSIONS: This longitudinal study shows that the ageing process is associated with prolongation of QTd, QTcd and Tpe after 4 years follow-up. The elderly Chinese subjects with the ACE D-allele had greater prolongation QTd and QTcd.     

QT-interval dispersion in acute myocardial infarction is only shortened by thrombolysis in myocardial infarction grade 2/3 reperfusion

BACKGROUND: Increased QT interval dispersion (QTd) has been found in patients with acute myocardial infarction (AMI). In previous studies this has been shown to decrease with thrombolysis. HYPOTHESIS: The aim of this study was to compare the effects of reperfusion by primary percutaneous transluminal coronary angioplasty (PTCA) and by thrombolysis on QTd and correlate these results with the degree of reperfusion. METHODS: We studied 60 patients with a first AMI. The study cohort included 40 consecutive patients who had received thrombolysis (streptokinase or rt-PA); 20 additional consecutive patients with successful primary PTCA, all with preselected Thrombolysis in Myocardial Infarction (TIMI) grade 3 flow by predefined selection criteria (12 stents); and 20 controls. A 12-lead ECG for QTd calculation was recorded before thrombolysis or PTCA and immediately after the procedure. All values were corrected according to Bazett's formula (QTcd). QTd and QTcd values before and after each procedure in three groups and the respective percent changes of deltaQTd and deltaQTcd were compared separately. RESULTS: QTd and QTcd were significantly increased before thrombolysis/PTCA versus normals. An angiogram performed after thrombolysis showed adequate reperfusion (TIMI grade 2/3) in 20 patients, while in the other 20 only TIMI 0/1 reperfusion was achieved. Thrombolysis-TIMI flow 2/3 and PTCA significantly reduced QTd (from 68 +/- 10 to 35 +/- 8 ms, p < 0.001, deltaQTd = 48 +/- 11%, in the Thr-TIMI flow 2/3 group,and from 79 +/- 11 to 38 +/- 9 ms, p < 0.001, deltaQTd = 52 +/- 9%, in the PTCA group), while in the Thr-TIMI flow 0/1 group no significant changes were recorded. A percent QTd decrease > 30 s had 96% sensitivity, 85% specificity, and 93% positive and 94% negative predictive value, respectively, for TIMI 2/3 flow. CONCLUSIONS: A significant decrease in QT dispersion may provide an additional electrocardiographic index for successful (TIMI 2/3) reperfusion.     

Dispersion of the QT interval in unstable angina pectoris

Increased dispersion of the QT interval is a risk factor of sudden cardiac death. In unstable angina pectoris (UA) a few authors described QT dispersion. The aim of the study was to assess QT dispersion in patients with UA in comparison to the healthy subjects and analysis QT dispersion according to the presence during in-hospital stay significant cardiac events like: death due to cardiological causes, myocardial infarction and urgent revascularization. Study group consisted of 54 patients with UA in a class IIIB of Braunwald classification (18 women, 36 men, mean age: 58.2 +/- 9.6 years). In 40 patients after pharmacological treatment stabilization in the first three days of hospitalization was achieved and during in-hospital stay significant cardiac events were not observed--group I. In 14 patients during in-hospital stay significant cardiac events were present, including 5 death due to cardiological causes--group II. During first two days of hospitalization coronary angiography was performed in all patients. The control group comprised 25 healthy subjects (8 women, 17 men, mean age 56.4 +/- 6.1 years). On admission to the hospital in all patients and in control group, using standard 12-leads ECG, following parameters were calculated: QT dispersion (QTd), corrected QT dispersion based on Bazett's formula (QTcd) and QT dispersion ratio (QTdR). In the study group as well as in group I and II values of QTd, QTcd and QTdR were significantly higher than in healthy subjects. In group I all the QT parameters were significantly lower than in group II (QTd: 56.8 +/- 11.2 vs 68.6 +/- 16.6 ms, p = 0.002). The highest value of QT dispersion was found in patients who died during in-hospital stay and it was significantly higher than in survivors (86.0 +/- 13.4 vs 57.1 +/- +/- 10.6 ms, p = 0.004). A cut-off value for QTdR > or = 9% identified patients with high risk of sudden cardiac death. CONCLUSIONS: QT dispersion analysis in unstable angina pectoris allows to distinguish patients according to the risk of sudden cardiac death. Patients with high risk of sudden cardiac death identify the best QTdR.     

Angioplasty decreases prolonged QT dispersion in patients with angina pectoris but not in patients with prior myocardial infarction

BACKGROUND AND HYPOTHESIS: Prolonged QT dispersion (QTd) is shortened by successful percutaneous transluminal coronary angioplasty (PTCA) in patients with ischemic heart disease. Particularly, QTd plays an important role in the prognostication in patients with prior myocardial infarction (MI). However, whether the effect of PTCA on QTd differs in patients with and without prior MI is not clear, and this study sought to clarify this question. METHODS: In 41 consecutive patients with ischemic heart disease, we measured QTd from a routine 12-lead electrocardiogram taken at 72 h before and after successful PTCA. Patients were divided into two groups based on the presence or absence of prior MI: Group 1 consisted of 24 patients with angina (61 +/- 11 years old) without prior MI and Group 2 was comprised of 17 patients (69 +/- 10 years old) with prior MI. QTd was calculated as the difference between the maximum and minimum QT and QT corrected for heart rate (QTc), using Bazett's formula for calculating QTcd. All measurements were obtained manually and blindly. RESULTS: In Group 1, 15 of 24 patients (63%) demonstrated multivessel disease and 16 of 24 (67%) patients had high QTd > 60 ms. Percutaneous transluminal coronary angioplasty decreased QTd and QTcd in Group 1 (QTd, from 83 +/- 35 to 57 +/- 19 ms, p < 0.05 ; QTcd, from 89 +/- 37 to 63 +/- 33 ms, p < 0.05), whereas no changes were observed in Group 2 (QTd, from 73 +/- 25 to 69 +/- 22 ms, NS; QTcd, from 80 +/- 30 to 79 +/- 28 ms, NS). QTd is more sensitive to decrease by successful PTCA in patients with angina than in patients with prior MI. CONCLUSIONS: The effect of successful PTCA on inhomogeneity of ventricular repolarization reflected by QTd in patients with prior MI is different from that in patients without prior MI.     

QT interval analysis in patients with chronic liver disease: a prospective study

In previous studies, it has been shown that QT interval prolongation is related to an increased mortality rate in chronic liver disease (CLD). But QT dispersion (QTd) and its clinical significance in CLD has not been well studied. The objectives of this study were to investigate the relation between QTd and severity of the disease and determine its prognostic value in cirrhotic patients. Thirty-three consecutive patients with cirrhosis and 35 sex- and age-matched healthy subjects were studied. QT intervals and QT dispersions were measured on admission, and all intervals were corrected for heart rate according to Bazett's formula. The authors analyzed the potential relationship between QT parameters and the disease severity according to Child-Pugh classification and compared these values between survivors and nonsurvivors after a 3-year follow-up. Child-Pugh classification is used to assess liver function in cirrhosis. Corrected QT (QTc) prolongations were found in 32% of patients with cirrhosis and 5.7% of the healthy controls (p <0.001). The prevalence of increased (>70 ms) corrected QT dispersion (QTcd) was 45% in patients with cirrhosis. According to Child-Pugh criteria: QTd, maximum QT interval (QTmax), corrected QTmax (QTcmax), and QTcd in class C were significantly higher than those of class A and B (p <0.05, for all comparison). But there was no significant difference between class A and B in QTmax, QTcmax, QTd, and QTcd. There were 10 (30%) deaths from all causes during 3-year follow-up in the study group. Cox regression analysis showed that QTd and QTcd were better mortality indicators than QTmax and QTcmax, and Child's classification was the best predictor for mortality among all variables. In conclusion, QT dispersion and corrected QT dispersion parameters were better mortality indicators than other QT interval parameters and also may give additional prognostic information in patients with chronic liver disease.     

Effects of atrial pacing on QT dispersion in patients with coronary artery disease without angina pectoris and ST segment depression.

The aim of this study was to investigate QT dispersion during atrial pacing in patients with coronary artery disease (CAD) without clinical ischemia, such as angina pectoris and ST segment depression. Thirteen patients with normal coronary arteries and 42 patients with CAD (12 with single-vessel, 16 with two-vessel and 14 with three-vessel disease) having no angina pectoris or ST segment depression during atrial pacing with maximum rate of 120/minute were enrolled in the study. Twelve-lead surface ECGs were recorded at 100 mm/second paper speed before pacing, at maximum pacing rate, and during the recovery period for measurement of QT interval parameters. Corrected QTd (QTcd) increased from 43.4 +/- 8.1 to 49.3 +/- 9.5 ms (p < 0.05) in the control group, from 46.1 +/- 8.1 to 74.3 +/- 7.7 ms (p < 0.0001) in the single-vessel disease group, from 48.5 +/- 10.4 to 93.8 +/- 22.1 ms in the two-vessel disease group (p < 0.0001), and from 49.7 +/- 13.6 to 128.5 +/- 31 ms (p < 0.0001) in the three-vessel disease group at peak atrial pacing period. A positive correlation was found between the severity of CAD and QTcd (r = 0.49, p < 0.0001). It was found that pacing-induced QTc dispersion identifies coronary disease extent, even when there is no ST depression or T wave inversion during pacing.     

QT dispersion and left ventricular hypertrophy in athletes: relationship with angiotensin-converting enzyme I/D polymorphism

BACKGROUND: QT dispersion (QTd) is a measure of inhomogeneous repolarization of myocardium and is used as an indicator of arrhythmogenicity. QTd is increased in myocardial hypertrophy secondary to systemic hypertension. The relation between left ventricular (LV) enlargement in endurance trained subjects and QTd is unknown. The cloning of the angiotensin-converting enzyme (ACE) gene has made it possible to identify a deletion (D)-insertion (I) polymorphism that appears to affect the level of serum ACE activity. The aim of this study was to assess whether physiologic left ventricular hypertrophy as a result of physical training is associated with an increased QT length or dispersion depending on ACE I/D polymorphism. METHODS: 56 endurance athletes and 46 sedentary subjects were included in this study, and they underwent both complete echocardiographic and electrocardiographic examination, the QT interval was measured manually as an average based on a 12-lead ECG. We also analysed ACE I and D allele frequencies in all patients. RESULTS: Athletes had a significantly increased LV mass (235.1 +/- 68.5 g vs. 144.9 +/- 44.5 g, p < 0.001) and corrected QTd (QTcd) (55.5 +/- 18.1 ms vs. 42.9 +/- 17.2 ms, p < 0.001) in comparison to control subjects. There was a positive correlation between left ventricular mass index and QTcd in athletes (r = 0.3, p = 0.024). Left ventricular mass and mass index in ACE DD, DI and II genotypes were significantly different (p < 0.001). QTcd was significantly different between ACE DD (63.2 +/- 12.8 ms) and ACE II (44.9 +/- 17.6 ms) genotypes in athletes (p < 0.05). CONCLUSION: These data show that myocardial hypertrophy induced by exercise training might be associated with increased QTd as observed in systemic hypertension and might be affected by ACE I/D polymorphism.     

Impact of age on QT interval and QT dispersion in healthy subjects: a regression analysis

OBJECTIVE: although the isolated effects of age on QT interval and QT dispersion (QTd) have been previously investigated, no data are available on the simultaneous effects of age and other physiological or lifestyle factors on QT interval and QTd in healthy subjects. We studied the effects of age, gender, body mass index, smoking status, and blood pressure on these electrocardiographic parameters. DESIGN: observational study. SETTING: academic medical centre. Participants and measurements: age, gender, body mass index, smoking status, and blood pressure were obtained from 191 consecutive healthy subjects (101 males and 90 females, age range 19-89 years). The subjects were divided into three groups according to their age: <30 (n=56), 30-65 (n=49), and >65 years (n=86). RESULTS: heart-rate corrected QT interval (QTc, Bazett's formula) progressively increased with advancing age (389+/-3 vs. 411+/-4 vs. 418+/-3 ms, means+/-SEM; P<0.01). By contrast, no differences in QTd were observed across the three groups (36+/-2 vs. 35+/-3 vs. 40+/-2 ms, P=NS). A multivariate regression analysis showed that age (P<0.01) and body mass index (P=0.04) independently predicted QT interval while gender was a weak (P=0.09) predictor of QTd. CONCLUSIONS: after adjusting for gender, smoking status, and blood pressure, age and body mass index independently predicted QT interval in healthy subjects. By contrast, age is not a predictor of QTd. The increase of QT interval associated with ageing and body mass index might be secondary to cardiac hypertrophy and myocardial action potential prolongation.     

冠心病介入治疗对QT离散度的影响

目的探讨冠心病介入治疗对QT离散度的影响。方法选择127例行冠状动脉造影且心电图资料完整的患者,据造影结果分为对照组42例,治疗组85例,分别测定QT离散度(QTd)及校正QT离散度(QTcd)并进行比较。结果(1)介入治疗前治疗组与对照组相比QTd及QTcd均明显延长,统计学上差异有显著性意义(P<0.05)。(2)介入治疗后QTd及QTcd明显缩短,与介入治疗前相比,统计学上差异有显著性意义(P<0.05)。(3)介入治疗后QTd及QTcd与对照组比较,差异无显著性意义(P>0.05)。结论成功的介入治疗可缩短QT离散度,改善心肌的复极离散程度,减少心脏危险事件的发生。     

冠状动脉旁路移植术对QT、QTc、JT离散度的影响

目的　探讨冠状动脉旁路移植术 (Coronary artery bypass graftings,CABG)对冠心病患者 QT间期离散度(QTd)、QTc离散度 (QTcd)及 JT离散度 (JTd)的影响。方法　测定 33例 CABG术前和术后的 QTd为 CABG组 ,并以 33例确诊为冠心病行冠状动脉造影 ,而暂未行 CABG手术和装支架的病人作对照组。结果　 1CABG前和对照组比较 QTd无显著增大 (P>0 .0 5 )。 2 CABG组术后病人的 QTd、QTcd及 JTd显著减小 (P<0 .0 5 )。 3对照组冠状动脉造影术后 QTd、QTcd及 JTd与术前比较 ,无明显改变 (P>0 .0 5 )。结论　 CABG能使 QTd、QTcd及 JTd减小     

PCI和CABG术对高龄慢性冠脉闭塞病变患者QT、QTc和JT离散度的影响及与心功能的相关性

目的对高龄冠心病患者行经皮冠状动脉介入治疗（PCI）和冠状动脉搭桥术（CABG）术前、后的QT间期离散度（QTd）、校正QT间期离散度（QTcd）、JT间期离散度（JTd）的变化及与心功能相关性的研究。方法利用标准同步12导联心电图和二维彩色多普勒超声心动图对51例行PCI和CABG手术前后的高龄冠心病患者的QTd、QTcd和JTd离散度和心功能进行检测。结果高龄冠脉闭塞患者PCI与CABG术后的QTd、QTcd及JTd较手术前均显著缩短（P<0.01）,高龄冠脉闭塞患者PCI与CABG术后的心功能指数（LVEF,E）明显增加（P<0.01）。高龄冠脉闭塞患者PCI与CABG术后的QTd及JTd的显著缩短与LVEF的增加呈正相关。结论对于高龄患者严重狭窄或完全闭塞的冠状动脉由于尚有存活心肌,再通后部分存活心肌可恢复电、机械功能,这对挽救这些存活心肌具有重要意义。     

Value of QT dispersion in diagnosis of restenosis after intracoronary stent implantation

We studied the ECGs of patients with single vessel disease before and after (long term) coronary stent implantation. The interlead variability of the QT interval, known as QT dispersion (QTd), is believed to reflect the regional variations in ventricular repolarization and, thus, may provide an indirect marker of arrhythmogenicity. There are no reliable noninvasive markers of significant restenosis after stent implantation. The effect of coronary revascularization on QTd in patients who underwent coronary stenting has not been investigated extensively. The aim of this study was to evaluate the value of QTd in predicting restenosis after intracoronary stent implantation. QTd with 12 lead surface ECG was measured in 48 patients (21 with restenosis and 27 without restenosis; 33 male; mean age, 58+/-10.8 years) before the procedure and after long-term follow-up (mean, 6.8+/-3.2 months). All patients had coronary angiographic control at the end of the follow-up period. QTd (as the difference between the maximum and minimum QT interval measured from 12 lead ECG) and rate-corrected QT (QTcd) were evaluated at rest. In 27 patients without restenosis, QTd and QTcd decreased from 58+/-14.4 and 62.8+/-20.4 ms to 26.3+/-9.2 and 29.6+/-10.6 ms in the long term follow-up, respectively (P<0.001). However, in 21 patients with restenosis, there was no significant change in QTd and QTcd intervals and they were still increased at the end of the long-term follow-up (P>0.05). In conclusion, increased QT interval dispersion may be an inexpensive and simple marker of restenosis after intracoronary stent implantation.     

QT dispersion as a predictor of arrhythmic events in patients with ankylosing spondylitis

OBJECTIVE: The aim of the study was to evaluate QT dispersion (QTd), an indicator of repolarization heterogeneity, and its relation to ventricular arrhythmias in patients with ankylosing spondylitis (AS). METHODS: A full history, clinical examination, electrocardiograms and 24-h Holter monitoring were performed in 88 AS patients and 31 volunteers of similar age and sex. Groups were compared based on electrocardiographic abnormality, QTd, arrhythmias and heart blocks. RESULTS: QTd and corrected QTd (QTcd) were significantly greater in AS patients than controls (QTd, 52.8 +/- 15.1 vs 35.5 +/- 8.9 ms, P: < 0.0001; QTcd, 60.3 +/- 16.1 vs 39.4 +/- 10.7 ms, P: < 0.0001). The magnitudes of these parameters were associated with the duration of the disease (QTd, r = 0.56, P: < 0.01; QTcd, r = 0.60, P: < 0.001). The frequency of ventricular extrasystoles was found to be correlated with QTd (r = 0.35, P: < 0.01) and QTcd (r = 0.33, P: < 0. 01). CONCLUSION: Involvement of the heart may be seen in AS during the early clinical course of the disease. QTd may give clues about the presence of arrhythmias and can be used as a new technique for the evaluation of asymptomatic patients. Earlier detection of cardiac involvement could alter the prognosis of the patients.     

Impacts of glycoprotein IIb/IIIa inhibition on QT dispersion after successful percutaneous coronary intervention

Coronary ischemia augments inhomogeneity in ventricular repolarization. Decrease in the QT dispersion (QTd) following restoration of coronary blood flow to the ischemic myocardium by successful percutaneous coronary intervention (PCI) is an expected outcome. The purpose of the study was to seek whether glycoprotein IIb/IIIa (GP IIb/IIIa) inhibition has additional beneficial effects on QT dispersion after angiographically successful PCI. The study involved 111 consecutive patients scheduled for elective coronary balloon angioplasty with or without stent implantation. Sixty patients (mean age 58 +/-9) were randomized to receive standard therapy including preprocedural aspirin, ticlopidine, and IV heparin, and 51 patients (mean age 54 +/-10) were randomized to receive additional IV tirofiban infusion before the lesion was crossed with the guidewire. Standard 12-lead simultaneous ECG recordings for the measurement of QTd and corrected QTd (QTcd) (calculated by using Bazett's formula) were obtained before and immediately after the procedure, and at the 6th, and 24th hours. Blood samples for detection of postprocedural myocardial damage (CK-MB and cTn-I) were taken before and immediately after the procedure, at the 6th, 12th, and 24th hours. In total, 128 stenoses were treated with PCI. Seventy of these lesions were in the standard therapy group and 58 in the tirofiban group. QTd and QTcd were not statistically different between the 2 groups before and immediately after the procedure and at the 6th hours, but at the 24th hour QTd and QTcd were significantly longer in the standard therapy group (p=0.047 and p=0.001, respectively). Postprocedural troponin-I elevation (B=0.692, p=0.037), maximum inflation pressure (B=0.182, p=0.001), and previous myocardial infarction (MI) (B=0.885, p=0.004) were defined as the predictors of the final QT dispersion at the 24th hour. QT dispersion significantly decreased after successful percutaneous coronary intervention. GP IIb/IIIa inhibition therapy was not superior by means of recovery of increased QT dispersion during the early hours of the intervention, but it prevented minor myocardial necrosis and provided more long-lasting recovery in QT dispersion as compared with heparin therapy. This impact of GP IIb/IIIa receptor inhibition on QTd may be a possible mechanism by which these drugs reduce cardiovascular events after PCI.     

Effects of Glycoprotein IIb/IIIa Inhibition on QT Dispersion in Patients with Unstable Angina and Non-Q-Wave Myocardial Infarction

Acute coronary ischemia augments inhomogeneity in ventricular repolarization, which significantly correlates with ventricular fibrillation. The effects of glycoprotein IIb/IIIa receptor inhibition on QT interval dispersion (QTd), and the effects of QTd changes on in-hospital, 30 day, and long-term cardiac events in patients with unstable angina (UA) and non-Q-wave myocardial infarction (MI) have not been investigated previously. Eighty-three patients presenting with Braunwald class IIIB UA or non-Q-wave MI were randomized to standard therapy (aspirin and unfractionated heparin, 42 patients) or tirofiban therapy: addition to standard therapy (41 patients). QT interval dispersion (QTd) and corrected QTd (QTcd) were measured prior to therapy, and 6, 24, 48, 72, and 96 hours after the initiation of the treatment. In both groups QTd and QTcd were higher than normal limits during the admission, prior to therapy. The first QTd and QTcd were not different between two groups; the remaining values were significantly lower in tirofiban group except the first and last QTd (p values for QTd at 6, 24, 48, 72, and 96 hours are 0.057, 0.045, 0.0006, 0.04, and NS, respectively, and for QTcd, they are 0.017, 0.046, 0.0004, 0.012, and 0.01, respectively). When the first QTd and QTcd compared to the following measurements in each group, the first significant decrease occurred at 6th hour (p = 0.004 for QTd, and 0.004 for QTcd) in tirofiban group, whereas in standard therapy group it was occurred at 48th hour (p = 0.02) for QTd, and 72nd hour (p = 0.019) for QTcd. While the incidence of in-hospital acute MI, recurrent refractory angina, and total major cardiac events were significantly lower in the tirofiban group (p = 0.03, 0.04, and 0.01, respectively) that early QTd recovery observed, the 30 day and long-term incidence of major cardiac events were not different between the two groups. GP IIb/IIIa receptor inhibition in addition to heparin treatment causes a faster recovery of increased QT dispersion, and the early recovery of QTd is associated with a reduction in in-hospital major cardiac events.