Relationship between rate-corrected QT interval and wall motion abnormalities in the setting of acute myocardial infarction

Diagnostic flowchart to estimate the morphology of left descending artery lesions by initial electrocardiogram in ST-elevation myocardial infarction

BACKGROUND

ST-segment deviations in an initial 12-lead electrocardiogram provide anatomical information in ST-elevation myocardial infarction (STEMI). A diagnostic flowchart was formulated to estimate the anatomical characteristics of a culprit left anterior descending artery (LAD).

METHODS

The present study analyzed 252 STEMI patients whose culprit lesions were confirmed to be LAD as an observational study. LAD morphology, wrapped (n = 26) or not (n = 226), and the positional relationship to first diagonal branch (n = 162 in proximal, n = 90 in distal lesions) were assessed. Their ST-segment deviations and such anatomical characteristics were examined.

RESULTS

Reciprocal ST depression in nonwrapped LAD was frequent in patients without diagonal branch flow (49.3%-18.8% in II, p < .01; 66.4%-36.3% in III, p < .01; 63.7%-30.0% in aVF, p < .01). ST elevation in inferior leads was the characteristics of wrapped LAD but was not the case in patients without diagonal flow (50%-0% in II, 60%-0% in III, and 60%-0% in aVF). ST elevation in lateral leads to the diagonal branch in nonwrapped LAD is more frequent for proximal than distal lesions (36.3% vs. 15.0% in I, p < .01; 50.7% vs. 16.3% in aVL, p < .01), but this was not observed for wrapped LAD (18.8% vs. 20.0% in I, p = .72; 31.3% vs. 10.0% in aVL, p = .21). Positive and negative predictive values for the diagnostic accuracy of suggested diagnostic flow based on the above results were 0.794 and 0.478, respectively.

CONCLUSIONS

Our suggested diagnostic flowchart provides enough diagnostic accuracy to estimate culprit morphology.

Prevalence and prognostic significance of long QT interval in patients with acute coronary syndrome: review of the literature

BACKGROUND

Sympathetic hyperactivity is linked with several adverse cardiovascular events in patients with acute coronary syndrome (ACS). Sympathetic activity increases early in the process of ischemia through 2 mechanisms. One originates from the central nervous system and leads to enhanced sympathetic activity. The other mechanism originates at the infarct zone and leads to B receptor up-regulation and catecholamine supersensitivity. Nevertheless, sympathetic hyperactivity accompanied by an underlying myocardial structural damage is likely to increase the ventricular repolarization duration measured as QT interval on the body surface electrocardiogram.

PURPOSE

The aims of the current review of the literature were to examine the physiological processes underlying the use of long QT interval as a risk prediction tool in patients with ACS and to critically review and critique the existing evidence related to this matter.

CONCLUSION

The available evidence is contradictory and includes serious limitations in design and QT measurement and correction. Until accurate and reliable data are available, it is difficult to determine the additional clinical value and prognostic significance of long QT interval in patients with ACS beyond that in other patients.

CLINICAL IMPLICATIONS

Long QT interval is not uncommon among patients with ACS. Automated continuous QT interval monitoring is superior to manual QT interval measurement with the standard 10-second electrocardiogram. Optimum care for patients with ACS requires nurses to keep monitoring the QT interval several days after the initial event.

Prevalence and prognostic significance of long QT interval among patients with chest pain: selecting an optimum QT rate correction formula

BACKGROUND

Little is known about the prevalence and prognostic significance of long QT interval among patients with chest pain during the acute phase of suspected cardiovascular injury.

OBJECTIVES

Our aim was to investigate the prevalence and prognostic significance of long QT interval among patients presenting to the emergency department (ED) with chest pain using an optimum QT rate correction formula.

METHODS

We performed secondary analysis on data obtained from the IMMEDIATE AIM trial (N, 145). Data included 24-hour 12-lead Holter electrocardiographic recordings that were stored for offline computer analysis. The QT interval was measured automatically and rate corrected using seven QTc formulas including subject specific correction. The formula with the closer to zero absolute mean QTc/RR correlation was considered the most accurate.

RESULTS

Linear and logarithmic subject specific QT rate correction outperformed other QTc formulas and resulted in the closest to zero absolute mean QTc/RR correlations (mean±SD: 0.003±0.002 and 0.017±0.016, respectively). These two formulas produced adequate correction in 100% of study participants. Other formulas (Bazett's, Fridericia's, Framingham's, and study specific) resulted in inadequate correction in 47.6 to 95.2% of study participants. Using the optimum QTc formula, linear subject specific, the prevalence of long QTc interval was 14.5%. The QTc interval did not predict mortality or hospital admission at short and long term follow-up. Only the QT/RR slope predicted mortality at 7year follow-up (odds ratio, 2.01; 95% CI, 1.02-3.96; p<0.05).

CONCLUSIONS

Adequate QT rate correction can only be performed using subject specific correction. Long QT interval is not uncommon among patients presenting to the ED with chest pain.

Relationship between infarction location and size to QT dispersion in patients with chronic myocardial infarction

The relationship between the location and size of an infarction and QT dispersion was investigated in 84 Japanese patients with chronic myocardial infarction (54 with anteroseptal infarction and 30 with inferior infarction). The control group consisted of 23 subjects without ischemic heart disease (13 normal subjects and 10 hypertensive patients). Corrected QT dispersion (maximum corrected QT interval minus minimum corrected QT interval: QTc dispersion), was significantly larger in the anterior infarction group than in the control group (69.9+/-21.5 msec vs 53.0+/-17.6 msec), while the inferior infarction group showed no significant difference from control subjects. QTc dispersion was significantly greater in the patients with large anterior infarcts than in those with small anterior infarcts (80.5+/-20.5 msec vs 61.9+/-18.8 msec). In patients with chronic myocardial infarction, QT dispersion is influenced by the infarct location and size. Accordingly, interpretation of QT dispersion data should take these factors into consideration.