Usefulness of QTc dispersion in interpreting exercise electrocardiograms

Effect of Direct Stent Implantation on QTc Dispersion

The aim of this study was to evaluate whether direct stenting is superior to conventional stent implantation technique with respect to QTc dispersion in prospectively selected patients with simple lesion morphology and class II stable angina undergoing elective coronary stenting. One hundred thirty-four consecutive patients were divided into 2 groups based on the stenting technique used: the direct stenting without predilation group, group I (n=64), and the stenting with predilation group, group II (n=70). All patients had single-vessel disease. The primary end point of the study was the QTc dispersion at the 24th hour and at the first month after the procedure and the secondary end point of the study was the major clinical events (MCEs) rate in the hospital period and up to 1 month. Baseline maximum QTc, minimum QTc, and QTc dispersion were not different between the 2 groups. QTc dispersion decreased from 47 ±8 msec before stent implantation to 41 ±11 msec at 24 hours and 37 ±7 msec 1 month after angioplasty in group I (p<0.006 and p<0.01, respectively), whereas QTc dispersion decreased from 49 ±9 msec before stent implantation to 46 ±8 msec at 24 hours and 42 ±10 msec 1 month after angioplasty in group II (p<0.03 and p<0.01, respectively). Compared with group II, the decrease in QTc dispersion was significantly greater at the 24th hour and at the first month after the procedure in group I (p<0.003 and p<0.001, respectively). There was a decreased trend toward MCE rate in group I in relation to that of group II, but the statistical difference was not significant. Direct stenting is a feasible and safe technique. It is superior to conventional stenting technique in decreasing the QTc dispersion at the 24th hour and at the first month after the procedure, whereas it is equivalent to single-vessel conventional stent implantation technique with respect to MCEs rate in the short-term period.

Electrocardiologic and Echocardiographic Features of Patients Exposed to Scorpion Bite

The purpose of this study is to examine clinical progress and hemodynamic and electrocardi ologic features (QT depression and heart rate variability [HRV]) of patients exposed to a scorpion bite.

Seventeen patients bitten by scorpions, and, as a control group, 15 healthy subjects were included in the study. Standard electrocardiograph (ECG) records, 24-hour Holter-ECG, and Doppler echocardiographic examinations were performed.

Holter ECG indicated sinus tachycardia, sinus bradycardia, paroxysmal supraventricular tachycardia, atrial fibrillation, first-degree and second-degree atrioventricular block not requiring treatment, early atrial beats, and early ventricular beats in the patients at frequen cies of 82%, 12%, 35%, 12%, 8%, 70%, and 47%, respectively.

HRV parameters that reflected parasympathetic activity (SD 35 ±13-43 ±16, RMS-SD: 20 ±9-30 ± 12, high frequency: 7.8 ±2-4.3 ±3, p<0.05) were significantly lower (p<0.05). Low frequency, which especially showed sympathetic activity (LF: 11 ± 13-11 ±23, p>0.05), was similar in both groups. In addition, the LF/HF ratio, which reflected sympathovagal balance, was significantly increased in the patient group (1.5 ±1-3.0 ±2, p = 0.005).

Corrected QT and QT dispersion values were not significantly different with respect to the control (p>0.05).

In the patient group compared to the control, a significant decrease was determined in the proportion of mitral E velocity to mitral A velocity (mEv/mAv), diastolic filling period (DFP), and left ventricular ejection fraction (LVEF), while a significant increase was noticed in pulmonary artery pressure (PAP) (mEv/mAv: 0.9 ±0.4-1.7 ±0.6, DFP: 362 ±8.5-425 ±89, LVEF: 53.1 ±6.7-68.6 ±5.8, PAP: 38.1 ±13-27.2 ±6, p<0.05).

Scorpion bite leads to serious cardiovascular disorders, associated with decreased HRV, decreased systolic and diastolic functions, increased arrhythmic events, and hemodynamic disturbance with sympathetic and parasympathetic balance disturbance.

Electrocardiography changes in bipolar patients during long-term lithium monotherapy

OBJECTIVE

Cardiovascular side effects of lithium have been reported to occur mainly at higher-than-therapeutic serum levels. We aimed to investigate the impact of the long-term lithium use on electrocardiogram (ECG) parameters in association with the serum levels in patients with bipolar disorder (BD) and in healthy controls (HCs) serving as the reference group.

METHODS

The study sample consisted of 53 euthymic BD type I patients on lithium monotherapy at therapeutic serum levels (M = 0.76, S.D. = 0.14, range = 0.41-1.09 mmol/l) for at least 12 months and 45 HCs. A 12-lead surface ECG was obtained from all participants at resting state for at least half an hour for 5-min recording. Heart-rate, Pmax, Pmin, QRS interval, QT dispersion, QT dispersion ratio (QTdR) and Tpeak-to-end interval (TpTe) were measured.

RESULTS

Regression analyses revealed that QTdR (B = 14.17, P = .001), TpTe (B = 18.38, P < .001), Pmax (B = 17.84, P<.001) and Pmin (B = 25.10, P < .001) were increased in BD patients who were on chronic lithium treatment than in HCs after controlling for age, sex and strict Bonferroni correction for multiple testing. There were no associations between serum lithium levels and ECG parameters.

CONCLUSION

Our findings suggest that the use of lithium is associated with both atrial and ventricular electrical instability, even when lithium levels are in the therapeutic range.

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.

Changes in QT dispersion during adenosine infusion

BACKGROUND

QT dispersion (QTd) measurement during treadmill stress testing has been to shown to improve the accuracy of exercise electrocardiogram (ECG) in the detection of significant coronary artery disease (CAD).

HYPOTHESIS

The aim of this study was to determine whether adenosine-induced changes in QTd could predict significant CAD and to assess its efficacy as a diagnostic index in patients undergoing adenosine stress test.

METHODS

QT interval measurements were made in 57 consecutive patients undergoing adenosine sestamibi stress test. Patients with an abnormal stress test underwent coronary angiography. Patients with significant disease by coronary angiography (> 70% stenosis) were classified as having CAD (Group 1), and those with normal stress images and/or normal coronaries by angiography were classified as having no CAD (Group 2).

RESULTS

QT dispersion increased from 28.2 +/- 4.5 to 43.8 +/- 4.5 ms with a delta QTd of 15.53 +/- 3.68 in Group 1 (p = 0.001) and from 28.4 +/- 2.6 to 34.8 +/- 2.8 ms with a delta QTd of 6.58 +/- 2.21 ms in Group 2 (p = 0.006). Patients in Group 1 had a significantly higher increase in QTd (delta QTd) than the patients in Group 2 (p < 0.03). Addition of delta QTd (> 10 ms) to the ST depression during adenosine infusion would increase the sensitivity of the ECG from 23 to 65% and decrease the specificity from 91 to 70% for diagnosis of significant CAD.

CONCLUSIONS

delta QTd is significantly more prolonged in patients with CAD during adenosine infusion. It increases the sensitivity of the stress ECG in diagnosis of CAD during adenosine infusion when used as an adjuvant index.

The association of QT dispersion and QT dispersion ratio with extent and severity of coronary artery disease

BACKGROUND

Although prolongation of the QT intervals in acute ischemic conditions, such as acute myocardial infarction, intracoronary balloon inflation, and exercise induced ischemia, has been shown, association of rest QT intervals with extent and severity of stable coronary artery disease (CAD) has not been assessed so far. The effects of extent and severity of stable CAD on rest QT interval were analyzed in this study.

METHODS

Rest 12-lead electrocardiograms (ECG) were recorded in 162 clinically stable subjects undergoing coronary angiography before the angiography for measurement of corrected QT dispersion (cQTd) and the QT dispersion ratio (QTdR) defined as QT dispersion divided by cycle length and expressed as a percentage. Angiographic "vessel score,""diffuse score," and "Gensini score" were used to evaluate the extent and severity of coronary atherosclerosis. Subjects were grouped as follows: those with normal angiogram (Group 1), those with insignificant (<50%) coronary stenosis (Group 2), and those with 1- (Group 3), 2- (Group 4), or 3-vessel disease (Group 5).

RESULTS

cQTd and QTdR were higher in Group 3 compared with Group 1 (P < 0.001 and P = 0.001, respectively), in Group 4 compared with Group 1 (P < 0.001 for both) and Group 2 (P = 0.001 and P = 0.003, respectively), and in Group 5 compared with Group 1 (P < 0.001 for both) and Group 2 (P < 0.001 and P = 0.003, respectively). cQTd and QTdR were positively correlated with the vessel score (r = 0.422, P < 0.001; r = 0.358, P < 0.001, respectively), diffuse score (r = 0.401, P < 0.001; r = 0.357, P < 0.001, respectively) and Gensini score (r = 0.378, P < 0.001; r = 0.373, P < 0.001, respectively). In multiple linear regression analyses, cQTd was found to be independently associated only with diffuse score (beta= 0.325, P = 0.038). Also, QTdR was independently associated with diffuse score (beta= 0.416, P = 0.006) and Gensini score (beta= 0.374, P = 0.011).

CONCLUSIONS

Rest cQTd and QTdR are increased, and related to the extent and severity of coronary atherosclerosis in patients with stable CAD.

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 in single coronary artery disease: is there a relation between QT dispersion and diseased coronary artery or lesion localization?

It has been shown that QT dispersion (QTD) increases during episodes of myocardial ischemia or infarction. However, no extensive data on the relation between the diseased coronary artery or the localization of stenosis and the QTD are available. The aim of the study was to examine the relation between QTD and diseased coronary artery and lesion localization during exercise stress test in patients with single coronary artery disease without prior myocardial infarction. One hundred nineteen patients with single coronary artery disease and 53 patients with normal coronary arteries were enrolled in study. All patients underwent exercise stress test with modified Bruce protocol, and QT interval parameters were measured at rest and at minute 2 of the recovery (rec-2) period. QT dispersion at rest was found higher in all single-vessel disease groups compared with that in the control group, and corrected QT dispersion at rec-2 period was also markedly higher in left anterior descending, circumflex, and right coronary artery groups compared with that in the control group. No relation was found between QT dispersion and diseased coronary artery or the lesion localization. In conclusion, no qualitative difference was found between QT dispersion and diseased coronary artery or proximal or distal lesion localization. However, it was observed that patients with single-vessel disease had wider baseline QT dispersion as compared with that in the control group, which further increased significantly with exercise. This finding supports the idea that severity of localized ischemia rather than extent of coronary artery disease would be expected to have a greater effect on inducible QT dispersion.

Effects of oral L-arginine supplementation on exercise-induced QT dispersion and exercise tolerance in stable angina pectoris

We assessed the effects of L-arginine (an endogenous precursor of nitric oxide) on the magnitude of exercise-induced QT dispersion in patients with coronary artery disease. The study had a randomized double-blind cross-over design. Twenty-five patients with stable coronary artery disease underwent two separate exercise tests: after oral administration of L-arginine (6 g/24 h for 3 days) or placebo. Indications for cessation of exercise included: pulse limit, exhaustion, chest pain, ST segment depression >2 mm. We found that arginine significantly increased exercise duration from 604+/-146 to 647+/-159 s (P<0.03). However, it had no effect on the sum of exercise-induced ST segment depressions (1.9+/-2.3 and 2.4+/-3.3 on and off arginine, respectively, NS). Exercise shortened QT interval to a similar extent in patients treated with placebo or arginine. QT dispersion changed during exercise from 55+/-21 to 60+/-19 ms (NS) and from 60+/-21 to 53+/-17 ms (NS), respectively. We conclude that, in patients with coronary artery disease, oral supplementation of L-arginine does not affect exercise-induced changes in QT interval duration, QT dispersion or the magnitude of ST segment depression. However, it significantly increases exercise tolerance, most likely due to improved peripheral vasomotion. These results may be of clinical and therapeutic importance.

Effects of metabolically ischemic, but viable, myocardium on QT dispersion in patients with acute myocardial infarction: a study with resting I-123-BMIPP/thallium-201 myocardial single-photon emission computed tomography

In chronic Q-wave myocardial infarction, QT dispersion is closely correlated with infarct size, but this correlation has not been evaluated for acute myocardial infarction (AMI). The effects of abnormal fatty acid metabolism on QT dispersion were examined in 123 patients with AMI who underwent resting iodine-123-15-iodophenyl 3-methyl pentadecanoic acid (BMIPP)/thallium-201(201Tl) myocardial single photon emission computed tomography (SPECT) and electrocardiographic analysis in the subacute phase. The relationship between BMIPP and 201Tl was defined as match when the total defect score for BMIPP was equal to or smaller than that for 201Tl, and as mismatch when the total defect score for BMIPP was larger than that for 201Tl. Twenty-six patients (21%) demonstrated BMIPP-201Tl match and 97 (79%) demonstrated mismatch. Infarct size was closely correlated with QT dispersion (r=0.67, p<0.001) in patients with BMIPP-201Tl match, but weakly correlated (r=0.30, p<0.005) in patients with BMIPP-201Tl mismatch. For small infarctions, QT dispersion was significantly larger in patients with BMIPP-201Tl mismatch than in those with BMIPP-201Tl match (62+/-24 ms vs 41+/-18 ms, p=0.03), but did not differ between the 2 groups for large infarctions. This study shows that QT dispersion is influenced by infarct size and by the presence of metabolically ischemic but viable myocardium in patients with AMI.

Improvement in corrected QT dispersion by physical training and percutaneous transluminal coronary angioplasty in patients with recent myocardial infarction

The aim of the present study was to assess whether physical training and percutaneous transluminal coronary angioplasty (PTCA) improve the corrected QT (QTc) dispersion in patients with recent myocardial infarction (MI). Twenty-four patients with recent MI were allocated to one of 3 groups: training (n = 8), PTCA (n = 7) or controls (n = 9). Physical training as well as PTCA decreased QTc dispersion, whereas QTc dispersion increased in the control group. Changes in QTc dispersion after physical training or PTCA were inversely correlated with exercise-induced ST depression at the baseline test. These observations suggest that physical training, as well as PTCA, could improve QTc dispersion and electrical instability in patients with recent MI, possibly due to improvement of myocardial ischemia.

Relation between QT dispersion and ventricular arrhythmias in uncomplicated isolated mitral valve prolapse

Complications of mitral valve prolapse (MVP), among which serious ventricular arrhythmia and sudden death are of major importance, affect many individuals due to the high incidence of MVP itself in the community despite the actual low incidence of these complications. The present study investigated the incidence and distribution of ventricular arrhythmias according to their severity and relationship with the QT interval and dispersion of repolarization in uncomplicated isolated MVP (IMVP) cases. Fifty-eight uncomplicated IMVP patients, 33 patients with accompanying tricuspid valve prolapse (TVP), to compare its relationship with ventricular arrhythmia, and 60 age- and sex-matched control subjects were enrolled in the study. Individuals with accompanying cardiac or systemic disease, or who were on drug therapy that could potentially affect QT characteristics, were excluded. The incidence of ventricular arrhythmia was 48% in the IMVP group and 64% in the TVP group; the difference was statistically insignificant. In addition, the differences of the QT and Q peak T values were insignificant, whereas QT dispersion (QTd) and Q peak T dispersion (QpeakTd) values were significantly higher in the patient group (60+/-14, 54+/-14 ms, respectively) compared with the control group (42+/-10, 38+/-10 ms, respectively, p<0.001). Complex ventricular arrhythmias (Lown Grade > or =III) in the IMVP group had a significant relationship with QTd and QpeakTd (p<0.001), but not with QT or QpeakT. As a result of the study, it is concluded that TVP accompanying MVP does not increase the incidence of ventricular arrhythmia, that ventricular arrhythmia is related to QT dispersion rather than QT interval in IMVP, that the QT dispersion is a fairly good marker for identifying the high-risk group for serious ventricular arrhythmia and sudden death, and that QpeakT dispersion measurement is an additional indicator that could be an alternative when QT is difficult to determine in conditions such as high heart rate or the presence of U wave.

Evaluation of autonomic influences on QT dispersion using the head-up tilt test in healthy subjects

Our objective was to examine the autonomic influence on QT interval dispersion using the head-up tilt test in healthy subjects. RR and QT intervals, heart rate variability, and plasma norepinephrine concentration were measured in the supine position and tilting to 70 degrees for 20 minutes using a footboard support in 15 healthy male volunteers (mean age +/- SD: 28.0 +/- 4.5 years). The rate-corrected QT interval (QTc) was calculated using Bazett's formula, and QT and QTc dispersions were defined as the maximum minus minimum values for the QT and QTc, respectively, from the 12-lead ECG. Spectral analysis of the heart rate variability generated values for the low- and high-frequency powers (LF and HF) and their ratio (LF/HF). Compared with values obtained in the supine position, tilting significantly increased QT (P < 0.05) and QTc dispersion (P < 0.01), the LF/HF ratio (P < 0.0001), and plasma norepinephrine concentration (P < 0.0001), and significantly decreased HF (P < 0.0001). QTc dispersion was positively correlated with the LF/HF ratio and plasma norepinephrine concentration, and negatively correlated with HF. These results suggest that head-up tilt testing increases QT dispersion by increasing sympathetic tone and/or decreasing vagal tone in healthy subjects.

Significance of exercise QT dispersion in patients with coronary artery disease who do not have exercise-induced ischemic ST-segment changes

The poor sensitivity and the poor predictive value of ST-segment depression have limited the usefulness of the exercise electrocardiogram (ECG) in the diagnosis and evaluation of coronary artery disease (CAD). The QT dispersion (QTD), recorded as the difference between maximal and minimal QT intervals on a 12-lead exercise ECG, is sensitive to myocardial ischemia and may improve the accuracy of exercise testing in patients with CAD who do not show an ST-segment depression. Exercise ECGs were analyzed in 50 subjects who had undergone coronary angiography for clinical indications. None of them showed an ST-segment depression during or after exercise: There were 25 patients with significant coronary artery stenosis and 25 without significant stenosis. The QTD measured before, immediately after, and 1 min after exercise was similar in the 2 groups. The QTD at 3 and 5 min after exercise was significantly greater in patients with CAD than in the controls, and the most marked difference in QTD was observed at 3 min after exercise. A QTD at 3 min after exercise of >60 ms had a sensitivity of 80% and specificity of 88% regarding the diagnosis of CAD. When a deltaQTD (post-exercise QTD minus QTD at rest) at 3 min after exercise of >0 ms was added to a QTD of >60 ms as a condition for positivity, the specificity increased to 96%. QTD measured at 3 min after exercise increases the accuracy of exercise testing in patients with CAD who do not show an ST-segment depression.

Relation of QT dispersion to infarct size and left ventricular wall motion in anterior wall acute myocardial infarction

Previous studies have shown that QT dispersion increases during acute myocardial infarction (AMI). However, the relation of QT dispersion to infarct size and left ventricular (LV) function in AMI has not yet been fully clarified. Accordingly, this study was conducted to elucidate this relation at 1 month after anterior wall AMI. We examined 94 patients with first anterior wall AMI (< or = 6 hours) who underwent coronary arteriography at admission, 1 month, and 6 months after AMI, and left ventriculography at 1 and 6 months after AMI. Mean QT dispersion on the chronic phase (about 1 month after AMI) electrocardiogram was 79 +/- 33 ms. There were no significant correlations between QT dispersion and peak creatine phosphokinase levels, LV ejection fraction, and regional wall motion in the infarct region at 1 month after AMI (r = 0.06, p = 0.57; r = 0.11, p = 0.29; r = -0.05, p = 0.63, respectively). In conclusion, the findings of this study suggest that QT dispersion on the resting electrocardiogram at 1 month after anterior wall AMI is unrelated to infarct size estimated by the peak creatine phosphokinase level and the degree of LV dysfunction.

Exercise-induced changes in the QT interval duration and dispersion in patients with sudden cardiac death after myocardial infarction

BACKGROUND

Prolongation of the QT interval and increased QT dispersion have been proposed to be associated with arrhythmic risk after myocardial infarction. However, controversy remains regarding the prognostic value of ventricular repolarization abnormalities in the risk stratification of patients surviving acute myocardial infarction. HYPOTHESIS AND OBJECTIVE: The QT interval is sensitive to myocardial ischaemia, and exercise-induced ischaemia may change the QT interval regionally, resulting in increased QT dispersion. This study examined whether there are abnormalities of ventricular repolarization during exercise and whether assessment of the exercise-induced changes in QT interval duration and dispersion would be able to differentiate patients at high risk from those at low risk of sudden cardiac death after myocardial infarction.

METHODS

Twenty-six post-myocardial infarction patients (mean age 54.5+/-8.9 years, 22 men) were retrospectively studied. Thirteen patients who died suddenly (SCD patients) during a follow-up of 39+/-6 months were compared to 13 patients who remained event-free, i.e. no ventricular tachyarrhythmias, no reinfarction, no by-pass (MI survivors). The two groups were pair-matched for age, gender, site of infarction, left ventricular ejection fraction and use of beta blocker. A further 13 patients with chest pain, normal coronary arteriograms and negative exercise test results were studied as controls. They were age and gender matched with the post-infarction patients. A 12-lead exercise ECG was recorded from each patient before, during and after exercise. QT and RR interval were measured on the exercise ECGs at each stage and QT dispersion was defined as the difference between the maximum and minimum QT intervals across the 12-lead ECG.

RESULTS

There were no significant differences in RR, QT and QTc (Bazett's and Fridericia's correction) intervals, or QT dispersion between any groups before exercise. A significant difference in QT and QT dispersion was found at peak exercise between post-infarction patients and controls (P=0.03 and P=0.0001, respectively), but no difference was observed between SCD patients and MI survivors. The maximum QTc at peak exercise was longer in SCD patients compared with MI survivors (P=0.02) and a maximum QTc>440 ms (Bazett's correction) was common in SCD patients but not in MI survivors or controls (62%, 15%, 15%, P=0.01). The differences in QT, QTc or QT dispersion observed at peak exercise were no longer significant after exercise.

CONCLUSIONS

Exercise-induced prolongation of the QTc interval differentiates patients at high risk of sudden cardiac death from those at low risk, whereas exercise-induced changes in QT dispersion failed to identify patients at high risk of sudden cardiac death after myocardial infarction.

Effect of coronary angioplasty on QT dispersion

Increased QT dispersion (QTmax-QTmin [QTd]) reflects inhomogeneous ventricular repolarization that may provide a substrate for serious arrhythmias and is associated with adverse clinical outcomes in patients with heart disease. Effective treatment of acute myocardial infarction or ventricular arrhythmias may reduce QTd, but the effect of coronary revascularization on QTd in patients without these conditions is unknown. In this study, QTd was measured before and 4 and 24 hours after successful angioplasty in 94 patients without ongoing symptomatic myocardial ischemia or malignant arrhythmias. QTd decreased from 434 +/- 17 msec before angioplasty to 354 +/- 15 msec 4 hours (p < 0.05) and 33 +/- 14 msec 24 hours after angioplasty (p < 0.05). QTd was improved in 64% of patients, worse in 28%, and unchanged in 8%. Thus angioplasty significantly improves QTd. This may reflect increased myocardial perfusion and may be inherently beneficial by reducing the propensity for arrhythmias.

Value of QT dispersion in the interpretation of exercise stress test in women

BACKGROUND

Exercise testing in women is associated with a high incidence of false-positive ECG changes and should be combined with an imaging study. The QT dispersion (QTD), recorded as the difference between maximum and minimum QT intervals on a 12-lead ECG, is sensitive to myocardial ischemia and may improve the accuracy of exercise testing in women.

METHODS AND RESULTS

Exercise ECGs were analyzed in 64 women who had undergone exercise ECG and coronary angiography for clinical indications: 20 patients with normal exercise stress test and nonsignificant (< or = 50% diameter narrowing of a major epicardial coronary artery) coronary artery disease (CAD) on angiography (true-negative; TN group), 20 patients with positive exercise stress tests (> or = 1 mm ST-segment depression or reversible perfusion defects) and significant CAD (true-positive; TP group), and 24 patients with positive exercise stress tests but no significant CAD (false-positive; FP group). The exercise QTD was 45+/-15 ms in TN, 80+/-23 ms in TP (P<.0001 versus TP), and 41+/-14 ms in FP (P=NS versus TN and <.0001 versus TP) groups. A stress QTD of > 60 ms had a sensitivity of 70% and specificity of 95% for the diagnosis of significant CAD compared with 55% (P<.05) and 63% (P<.01), respectively, for > or = 1 mm ST-segment depression during stress. When QTD of > 60 ms was added to ST-segment depression as a condition for positive test, the specificity increased to 100%.

CONCLUSIONS

Exercise QTD is an easily measurable ECG variable that significantly increases the accuracy of exercise testing in women.