Effect of balloon inflation-induced acute ischemia on QT dispersion during percutaneous transluminal coronary angioplasty

T-wave changes in patients with Wellens syndrome are associated with increased myocardial mechanical and electrical dispersion

Some patients with unstable angina and critical stenosis of the left anterior descending coronary artery (LAD) present with Wellens syndrome (WS), i.e., inverted or biphasic T-waves in the anterior precordial leads. We assessed clinical, angiographic, electro- and echocardiographic characteristic of patients with WS. In this retrospective study, clinical, angiographic, electro- and echocardiographic characteristic of 35 patients with WS were compared to 57 patients with critical LAD stenosis and normal resting electrocardiogram (ECG), and 45 subjects with normal coronary angiogram. QTc dispersion was measured from the 12-lead ECG as the difference between longest and shortest QTc intervals. Mechanical dispersion was defined as the time difference between the longest and shortest contraction durations which were measured as the time from the first deflection of the QRS complex to maximum myocardial shortening of each 18 segmental longitudinal strain curves derived by speckle tracking echocardiography. There were no significant differences in the complexity and location of the LAD lesion, anterograde and collateral flow in LAD and coronary artery dominance between patients with WS and normal ECG (P > 0.05, for all). Patients with WS had lower global longitudinal strain (GLS) and more pronounced both QTc and myocardial mechanical dispersion than patients with critical LAD stenosis and normal ECG, and control subjects (P < 0.05). T-wave changes in patients with WS are associated with more profound regional myocardial dysfunction and increased QTc and myocardial mechanical dispersion. Similar angiographic characteristics of the LAD lesion were seen in patients with WS and normal ECG.

Impact of myocardial reperfusion status on QT dispersion after successful recanalization of the infarct-related artery in acute myocardial infarction

OBJECTIVE

To determine whether adequate myocardial perfusion status after transluminal recanalization is associated with prompt improvement of QT dispersion (QTd).

BACKGROUND

Transluminal recanalization of the infarct-related coronary artery in acute myocardial infarction aims to promptly restore myocardial perfusion, to maximize electrical and mechanical recovery. QTd represents the heterogeneity of ventricular repolarization, which may affect electrical stability.

METHODS

Forty patients who underwent primary percutaneous coronary intervention for their first anterior acute ST-elevation myocardial infarction were prospectively enrolled. Myocardial reperfusion status was assessed by myocardial blush grade (MBG) on the final angiogram after successful recanalization (Thrombolysis In Myocardial Infarction Grade 3 flow).

RESULTS

Preprocedural QTd was similar in patients with final MBG 0-1, 2, and 3 (76 ± 24, 67 ± 13, and 69 ± 13 milliseconds, respectively; P = 0.661). After recanalization, QTd decreased in patients with MBG 3 (39 ± 16 milliseconds, P < 0.001) but not in patients with MBG 0-1 (74 ± 20 milliseconds) or MBG 2 (82 ± 16 milliseconds). Multivariate analysis showed that postprocedural MBG was an independent predictor of QTd after recanalization (standardized regression coefficient = -0.628, P < 0.001).

CONCLUSIONS

Adequate tissue perfusion may be crucial for electrical stability of the myocardium after reperfusion.

QT interval dispersion pattern in patients with acute ischemic stroke: Does the site of infarction matter?

BACKGROUND

QT interval dispersion (QTD) is an independent predictor of outcome following acute neurological events.

OBJECTIVES

To explore QTD patterns and their relation to the affected cerebral region in patients with acute ischemic stroke.

METHODS

Thirty patients with first acute ischemic stroke (the first stroke the patients had ever experienced) (study group) and 30 healthy controls (control group) were enrolled. Patients underwent magnetic resonance imaging to confirm and localize cerebral damage. Patients in the study group were further subdivided according to the site of infarction into four subgroups - namely, cortical, subcortical, brain stem and cerebellar infarctions, as well as according to insular involvement. All included subjects underwent 12-lead electrocardiography to measure QTD and corrected QT dispersion (QTcD).

RESULTS

In the study group, both QTD and QTcD on the first hospitalization day were significantly higher than in the control group (P<0.05 for both). Similarly, in the study group, both QTD and QTcD values on the first hospitalization day were significantly higher than the respective values on the third day (P<0.001 for both). No significant differences were found among the four territorial subgroups, or between right- and left-sided subgroups, regarding QT interval measurements, whether on the first or third day (P>0.05 for all). However, 'first-day' QTD and QTcD of patients with insular involvement were significantly higher than in those without such involvement (P<0.001 for both).

CONCLUSIONS

Both QTD and QTcD increased significantly in patients with acute ischemic stroke during the first hospitalization day. This increase of 'first-day' QTD and QTcD was significantly higher in patients with insular involvement than in those without such involvement.

Earliest time of change in QT dispersion after stenting in patients with single vessel coronary artery disease

Dispersion of the QT interval (QTd) is a measure of inhomogeneity of ventricular repolarization, and its prolongation may provide a suitable substrate for life-threatening ventricular arrhythmias. The present study was performed to determine the onset time of change in the corrected QT (QTc) interval and QTd in patients with stable angina and single vessel coronary artery disease. Electrocardiograms of 60 patients with successful stenting, obtained 1 h before and 1 h, 6 h, 12 h and 24 h after the procedure were analyzed. The QTc interval, QTc maximum, QTc minimum and QTd were measured. All electrocardiograms were scanned, and then underwent computer-based analysis. There was a significant reduction in the mean QTc interval as early as 12 h after the procedure (from 474±41 ms to 460±31 ms; P<0.001), which persisted to the 24 h follow-up. This was associated with a significant reduction in mean QT maximum (from 496±31 ms to 418±66 ms; P<0.001) and a significant prolongation in mean QT minimum (from 403±21 ms to 444±12 ms; P<0.001) at the same time intervals. Therefore, successful stenting of coronary arteries in patients with single vessel coronary artery disease and stable angina decreases QTd as early as 12 h after the procedure. This phenomenon may be the result of improved regional myocardial circulation, and reduced ischemia. A persistently low QTd in the following months may therefore have prognostic significance, and can be used as a noninvasive marker of stent patency. Further studies are necessary to define the clinical applicability of QTd in the assessment of long-term stent patency in such patients.

Would corrected QT dispersion predict left ventricular hypertrophy in hypertensive patients?

AIMS

We explored whether QT corrected dispersion (QTcD) can identify left ventricular hypertrophy (LVH) in hypertensives.

METHODS

We enrolled 100 hypertensive patients (study group) and 30 normotensive subjects (control group). Echocardiography was performed to measure left ventricular mass and left ventricular mass index. Electrocardiogram was performed to measure QTcD.

RESULTS

LVH was present in 42 patients (42%) of the study group, none among controls. Hypertensive patients had significantly greater indices of LVH and QTcD compared with controls (p <0.001 for all). Similarly, among hypertensive patients, those with LVH had a significantly greater QTcD compared with those without (p <0.001). Pearson's correlation coefficient test demonstrated strongly positive correlations between QTcD and the indices of LVH (p <0.001 for all). Analysis of the receiver operating characteristic curves identified 60 ms as the optimal cut-off value of QTcD that best predicts LVH in hypertensives. Using this value, QTcD was able to predict LVH with a sensitivity of 92.9% and specificity 98.2%.

CONCLUSIONS

QTcD is significantly increased in hypertensive patients with LVH compared with those without, being strongly correlated with the indices of LVH. A QTcD cut-off value of 60 ms predicted LVH in hypertensive patients with a high sensitivity and specificity.

QT dispersion before and after coronary artery angioplasty: a case study from Iran

AIM

In this study, we investigated the changes in QT dispersion (QTd) after successful coronary artery revascularization.

BACKGROUND

QTd, as a marker of regional variability of myocardial repolarization, increases following impaired myocardial perfusion and is associated with increased risk of ischemia-induced arrhythmia.

METHODS

In 45 consecutive patients (mean age 54.39±11.49 years) undergoing elective percutaneous coronary intervention (PCI), QTd was measured from a 12-lead electrocardiogram 6-12 hours before and 6 hours after the procedure. QTd was defined as the difference between maximum and minimum QT interval in the 12 leads. QT changes were analyzed regarding preoperative ejection fraction (EF), type and number of involved vessels, type and number of revascularized coronary arteries and history of Q-wave MI using SPSS software.

RESULTS

QTd significantly decreased postoperatively from 55.48±20.03 to 42.00±19.96 in the study population (P=0.001). Subgroup analyses showed that QTd did not decrease significantly in patients with two-vessel disease and those with low EF (<50%); however, the reduction was significant for other subgroups.

CONCLUSION

Successful PCI results in improved regional heterogeneity of myocardial repolarization, evidenced as decreased QTd after the procedure.

QT Interval and QT Dispersion in Patients Undergoing Hemodialysis: Revisiting the Old Theory

AIMS

We sought to explore the response of the corrected QT (QTc) interval duration and QT dispersion (QTD) to hemodialysis.

METHODS

We enrolled 50 patients with end-stage renal disease undergoing regular hemodialysis. Blood samples were drawn for measurement of serum electrolytes, and a 12-lead ECG was performed to measure the QTc interval duration and QTD, immediately before and just after dialysis sessions.

RESULTS

The mean age of the cohort was 42.8 ± 12.2 years (58% males). Both the QTc duration and QTD showed marked variability after hemodialysis. A significant correlation was found between the decrease of both serum potassium and magnesium levels after dialysis and the post-dialysis QTc interval duration, with Pearson's correlation coefficients r = -0.43 and r = -0.34, p = 0.002 and p = 0.01, respectively. Patients with a post-dialysis increase of QTc interval duration had a significantly higher percentage of reduction of serum potassium (p = 0.029), whereas patients with a post-dialysis increase of QTD had a significantly higher percentage of reduction of serum magnesium (p = 0.03).

CONCLUSION

Our findings suggest a highly variable response of the QTc interval duration and QTD to hemodialysis. The post-dialysis QTc interval duration inversely correlated with the decrease of both serum potassium and magnesium levels after dialysis.

QT Dispersion: Does It Change after Percutaneous Coronary Intervention?

BACKGROUND

Myocardial ischemia is one of several causes of prolonged QT dispersion. The aim of this study was to evaluate the effect that percutaneous coronary intervention has on the depolarization and repolarization parameters of surface electrocardiography in patients with chronic stable angina.

METHODS

We assessed the effects of full revascularization in patients with chronic stable angina and single-vessel disease who underwent percutaneous coronary intervention. Twelve-lead electrocardiograms were recorded before intervention and 24 hours subsequently. We measured parameters including QRS duration, QT and corrected QT durations, and JT and corrected JT duration in both electrocardiograms and compared the values.

RESULTS

There were significant differences between the mean QRS interval (0.086 ± 0.01 sec vs. 0.082 ± 0.01 second; p value = 0.01), mean corrected QT dispersion (0.080 ± 0.04 sec vs. 0.068 ± 0.04 sec; p value = 0.001), and mean corrected JT dispersion (0.074 ± 0.04 sec vs. 0.063 ± 0.04 sec; p value = 0.001) before and after percutaneous coronary intervention. No significant differences were found between the other ECG parameters.

CONCLUSION

Our data indicate that the shortening of corrected QT dispersion and corrected JT dispersion in patients undergoing percutaneous coronary intervention is prominent.

Apolipoprotein B and Cardiovascular Disease Risk: Position Statement from the AACC Lipoproteins and Vascular Diseases Division Working Group on Best Practices

Background: Low-density lipoprotein cholesterol (LDL-C) has been the cornerstone measurement for assessing cardiovascular risk for nearly 20 years.

Content: Recent data demonstrate that apolipoprotein B (apo B) is a better measure of circulating LDL particle number (LDL-P) concentration and is a more reliable indicator of risk than LDL-C, and there is growing support for the idea that addition of apo B measurement to the routine lipid panel for assessing and monitoring patients at risk for cardiovascular disease (CVD) would enhance patient management. In this report, we review the studies of apo B and LDL-P reported to date, discuss potential advantages of their measurement over that of LDL-C, and present information related to standardization.

Conclusions: In line with recently adopted Canadian guidelines, the addition of apo B represents a logical next step to National Cholesterol Education Program Adult Treatment Panel III (NCEP ATPIII) and other guidelines in the US. Considering that it has taken years to educate physicians and patients regarding the use of LDL-C, changing perceptions and practices will not be easy. Thus, it appears prudent to consider using apo B along with LDL-C to assess LDL-related risk for an interim period until the superiority of apo B is generally recognized.

A simple ECG marker for the detection of coronary restenosis after successful coronary angioplasty

BACKGROUND

The dynamic nature of QT dispersion (QTd) and the absence of an acceptable normal value suggest that the relative change not the absolute value of QTd would be a better predicator of coronary restenosis. We sought to examine the usefulness of the relative change in QTd, compared to the absolute value, as a predictor for coronary restenosis after previously successful percutaneous transluminal coronary angioplasty (PTCA).

METHODS

Ninety-two patients with a history of successful PTCA who were referred for coronary angiography (CA) for exclusion of coronary restenosis were included in this analysis. QTd was calculated as the difference in milliseconds between the maximum and minimum QT interval in the 12-lead ECG. Relative change in QTd was measured as [QTd at the time of angiography (current) - QTd after the successful PTCA (baseline)]/QTd (baseline) %. Receiver operating characteristics (ROC) analysis was used to detect the best cut-off point and also to compare the diagnostic accuracy of the relative change in QTd vs. the absolute QTd for prediction of coronary restenosis.

RESULTS

The relative change in QTd showed a significantly larger ROC area under curve (AUC) compared to the absolute QTd [AUC (95% CI): 0.79 (0.698, 0.872) and 0.61 (0.498, 0.703) respectively; p=0.011 for AUCs comparison]. The best cut-off point for the relative QTd was 40%, and for the absolute QTd this was 50 ms. The sensitivity and specificity of > or =40% increase in QTd to detect coronary restenosis was 71% and 83%, with positive and negative predictive values of 90% and 57%, respectively. The diagnostic accuracy of the absolute value of QTd was much less than this; the sensitivity and specificity of QTd > or =50 ms were 48% and 58%, with positive and negative predictive values of 71% and 34%, respectively.

CONCLUSIONS

Compared to the absolute value, the relative change in QTd is a better predictor of coronary restenosis after a previously successful PTCA. These findings may open the door for rethinking the use of QTd as a simple ECG predictor for cardiovascular outcomes.

Chronic administration of carvedilol improves cardiac function in 6-month-old Syrian cardiomyopathic hamsters

Heart failure (HF) is a multifactorial and progressive disease that has been linked to activation of the renin-angiotensin and sympathetic systems. In recent years, beta-blockers have been shown to improve the status of HF patients, although the precise mechanisms remain unclear. The present study evaluates the effect of beta-blockade with carvedilol (1 mg/kg/day) on cardiovascular function in 2- and 6-month-old cardiomyopathic hamsters (SCH) after 1-month and 5-month treatment periods with the drug, respectively. Age-matched golden hamsters were used as controls (CT). Systolic blood pressure (SBP) and echocardiographic studies were evaluated. The latter studies included left ventricular end-systolic (LVESV) and end-diastolic (LVEDV) volumes, ejection fraction (EF), cardiac output index (COI), heart rate (HR), and left ventricular posterior wall thickness (LVPWT). In 2-month-old SCH, carvedilol administration during a 1-month period reduced SBP from 107.59 +/- 3.49 to 77.26 +/- 3.49 mm Hg (n = 5, p < 0.05). At this stage, cardiac parameters in SCH were similar to those of controls and were not affected by carvedilol administration. In 6-month-old SCH, 5-month administration of carvedilol decreased SBP from 102.16 +/- 3.61 to 90.60 +/- 2.80 mm Hg (n = 5, p < 0.05), HR from 363 +/- 14 to 324 +/- 14 bpm (n = 5, p < 0.05), and LVESV from 0.18 +/- 0.01 to 0.13 +/- 0.01 ml/100 g BW (n = 5, p < 0.05), and increased EF and COI by 14 and 23%, respectively (n = 5, p < 0.05). The drug did not modify LVEDV or LVPWT. These results reveal that carvedilol significantly improves cardiac function in 6-month-old cardiomyopathic hamsters, but it does not prevent ventricular dilatation. Improved cardiac function appears to be secondary to decreased total peripheral resistance, due mainly to the vasodilator properties of the drug. Thus, overactivation of the sympathetic system is not likely to be a determining factor in the etiology of dilated cardiomyopathy in this animal model.

The immediate and short-term effect of successful percutaneous coronary intervention on repolarization in acute myocardial infarction patients

OBJECTIVES

The primary objective was to assess the immediate and short-term impact of successful percutaneous coronary intervention (PCI) on QT dispersion (QT disp) and corrected QT dispersion (QTc disp). Secondarily, the impact of PCI on QT and QTc disp within different infarct-related arteries and the impact of successful PCI in these different arteries were evaluated.

METHODS

Patients (n = 140, age 61.6 +/- 12.9, 69% male) undergoing direct primary PCI for acute MI were evaluated. Twelve-lead ECGs were obtained before (baseline), immediately after (0 h), 24hours after, and 3 days after PCI. The QT and QTc interval in each of the 12-leads were measured and the shortest interval was subtracted from the longest to derive the QT disp and QTc disp, respectively.

RESULTS

Angiography showed blockages in the left anterior descending, right coronary artery, and circumflex in 37.1, 48.9, and 15.0% of patients, respectively. Overall, 97 patients achieved successful reflow. QT and QTc disp were significantly improved in the group with successful reflow at each follow-up time after PCI versus baseline and corresponding values in the unsuccessful reflow group. QT disp was improved among patients with successful reflow irrespective of which infarct artery was responsible for the acute myocardial infarction.

CONCLUSIONS

Successful reflow with PCI is associated with a rapid reduction in QT disp and QTc disp that is maintained for at least 3 days after the event. Conversely, unsuccessful reflow was not associated with significant reductions in QT or QTc disp.

Effect of percutaneous coronary intervention of nonacute total coronary artery occlusions on QT dispersion

BACKGROUND

Myocardial ischemia is one of several potential causes of increased QT dispersion (QTd) in patients with nonacute total coronary artery occlusions (TCOs). We sought to assess the effect of percutaneous revascularization (PCI) of TCO on QTd and the relationship between QTd and long-term vessel patency.

METHODS

Seventy patients enrolled in the TOSCA were analyzed. Patients were undergoing PCI of a TCO > 72 hours' duration. Two independent reviewers measured QTd from electrocardiograms done immediately before PCI (PRE), 12 to 18 hours after PCI (POST), and then at 6 months (6M). Follow-up angiography was performed at 6 months.

RESULTS

Mean QTd decreased from PRE (77 +/- 29 milliseconds) to POST (66 +/- 26 milliseconds, P < .001) and 6M (65 +/- 25 milliseconds, P < .001). Patients with the same or longer QTd at 6 months compared with POST (POST < or = 6M) had significantly higher risk of failed target-vessel patency (odds ratio 10.3, 95% CI 1.24-84.8) than patients with QTd reduction at 6M versus POST values.

CONCLUSION

Revascularization of TCO resulted in a decrease in QTd, which was sustained at 6M. This suggests that PCI to a TCO has a beneficial effect on stabilization of the underlying ischemic substrate. Furthermore, absence of QTd reduction at 6M versus POST was associated with increased risk of failed target-vessel patency.

Prognostic implications of echocardiography in advanced heart failure

PURPOSE OF REVIEW

The growing epidemic of systolic congestive heart failure mandates strategies to identify accurately people with high morbidity and mortality. Echocardiography remains the most widely available noninvasive tool for the assessment of cardiac structure, function, and hemodynamics. Clinical data paired with echocardiographic analysis in patients with systolic heart failure obtained from a variety of investigations have allowed for the evaluation of this modality as a prognostic tool.

RECENT FINDINGS

Detailed appraisal of the literature has revealed five distinct, easy-to-evaluate echocardiographic parameters that may assist clinicians to segregate high-risk patients. The presence of or the inability to modify a left ventricular ejection fraction less than 25%, impaired right ventricular function (assessed by any of four methods), left ventricular end-diastolic dimension greater than 6.5 to 7 cm, a restrictive mitral inflow, or pulmonary hypertension (peak tricuspid regurgitant velocity >2.5 m/s) should alert clinicians of patients with high morbidity (recurrent congestive heart failure admission, arrhythmia, impaired functional capacity) and mortality. Particularly important among these variables is the presence of a restrictive mitral inflow pattern.

SUMMARY

Detailed analysis of two-dimensional and Doppler data routinely obtained from echocardiograms has established prognostic implications among patients with systolic heart failure. Although prospective clinical trials are lacking, the use of echocardiography to segregate risk should be incorporated into current strategies to treat congestive heart failure and influence clinical listing for cardiac transplantation.

QT dispersion measured by an automatic continuous method early in patients admitted for chest pain

BACKGROUND

There is a need for risk markers in patients with acute chest pain. QT dispersion (QTd) is a prognostic marker in several groups of patients. A problem with the manual measurement of QTd is operator dependency. This can be avoided by using an automatic method. We investigated QTd, derived from multiple automatic measurements, as a risk marker in a population with chest pain.

METHODS

In 548 patients admitted to the coronary care unit for chest pain and nondiagnostic ECG, 12-lead ECG recordings were collected each minute during the initial 17 h. From recordings with > or =10 valid leads, mean QTd (QTdMean), QTd in the first satisfactory recording and estimates of variability of QTd were computed and correlated to outcome.

RESULTS

In the group with QTdMean > or =40 ms (n=277), 10 patients died during the initial 30 days; one patient died in the group with QTdMean <40 ms (n=271) (P=0.07). During follow-up (median 6 months), 19 vs. five patients died in each group (P=0.03). The figures for the triple endpoint death/myocardial infarction/revascularisation were 52 vs. 27 events during the initial 30 days (P=0.018) and 76 vs. 41 events during follow-up (P=0.003). QTd in the first recording did not predict new cardiac events.

CONCLUSIONS

QTd measured as the mean value of multiple recordings was found to be a powerful marker for cardiac events during follow-up. It was superior to the analysis of QTd in a single ECG. It can be used for the selection of low-risk patients, but was not effective in identifying high-risk patients.

Hypertriglyceridemia: a review beyond low-density lipoprotein

Hypertriglyceridemia is made up of a complex array of dyslipidemias. Difficulties in establishing the independent predictive value of elevated triglycerides in coronary artery disease arise because the triglyceride-rich lipoprotein particles that accumulate are diverse, with differential atherogenic potential, and because hypertriglyceridemia states are typically associated with low high-density lipoprotein cholesterol. When high-density lipoprotein cholesterol is considered in multivariate analysis of the role of hypertriglyceridemia in coronary artery disease, the importance of elevated triglycerides pales, emerging as a statistical second fiddle. However, recent data have affirmed the primary role of triglycerides in the genesis of atherosclerosis. This process involves the overabundance of triglyceride-rich lipoprotein particles, which, paradoxically, can be enriched with cholesterol through the action of cholesterol ester transfer protein. These particles appear to be especially atherogenic. Also, low-density lipoproteins become smaller and denser-small, dense phenotype or pattern B-in hypertriglyceridemia states. This profile is associated with a threefold increase in coronary artery disease risk and is not evident on routine lipid testing. Aggressive management of hypertriglyceridemia requires more detailed lipid analyses to identify patients at risk. In treating hypertriglyceridemia, a risk factor beyond low-density lipoprotein would allow a broader definition of patients at risk for coronary artery disease so that more people would benefit from lipid-lowering initiatives.

Use of intracoronary electrocardiography for detecting ST-T, QTc, and U wave changes during coronary balloon angioplasty

Intracoronary electrocardiography (IC-ECG) is a more sensitive method than surface ECG to detect electrical changes during percutaneous transluminal coronary angioplasty (PTCA). It also provides direct monitoring of ST-T segment, QTc intervals, and U-wave genesis during balloon inflation. These changes are reflective of myocardial ischemia. The authors studied the effect of transient myocardial ischemia on ST-T segment, QTc intervals, and U-wave appearance by comparing standard and perfusion balloon angioplasty. PTCA of left anterior descending artery was performed in 14 patients using the standard balloons and in 11 patients using the perfusion balloons. Patients with perfusion balloon angioplasty had less ST-T elevation (0.15 +/- 0.05 mV versus 1.04 +/- 0.19 mV, P < 0.001), less QTc-shortening intervals (0.01 +/- 0.02 seconds versus -0.05 +/- 0.04 seconds, P < 0.001), and less positive U waves (two versus nine). The authors concluded that balloon angioplasty with perfusion balloons is associated with less ischemia as reflected by ST-T, QTc-shortening intervals, and U-wave changes. There was more positive U-wave appearance with the standard balloon angioplasty, which implies more ischemia. In addition, QTc-shortening intervals are associated with the development of U waves during standard balloon angioplasty. These findings suggest that IC-ECG is a sensitive tool in detecting myocardial ischemia. IC-ECG may also help to clarify the nature of chest pain during PTCA in some patients. Like QT dispersion (QTd), QTc-shortening intervals and new U waves can have prognostic implications and additional studies are needed to define this role.

Measurement, interpretation and clinical potential of QT dispersion

QT dispersion was originally proposed to measure spatial dispersion of ventricular recovery times. Later, it was shown that QT dispersion does not directly reflect the dispersion of recovery times and that it results mainly from variations in the T loop morphology and the error of QT measurement. The reliability of both automatic and manual measurement of QT dispersion is low and significantly lower than that of the QT interval. The measurement error is of the order of the differences between different patient groups. The agreement between automatic and manual measurement is poor. There is little to choose between various QT dispersion indices, as well as between different lead systems for their measurement. Reported values of QT dispersion vary widely, e.g., normal values from 10 to 71 ms. Although QT dispersion is increased in cardiac patients compared with healthy subjects and prognostic value of QT dispersion has been reported, values are largely overlapping, both between healthy subjects and cardiac patients and between patients with and without adverse outcome. In reality, QT dispersion is a crude and approximate measure of abnormality of the complete course of repolarization. Probably only grossly abnormal values (e.g. > or =100 ms), outside the range of measurement error may potentially have practical value by pointing to a grossly abnormal repolarization. Efforts should be directed toward established as well as new methods for assessment and quantification of repolarization abnormalities, such as principal component analysis of the T wave, T loop descriptors, and T wave morphology and wavefront direction descriptors.