M. Juhani Koistinen

Dispersion of QT interval in patients with and without susceptibility to ventricular tachyarrhythmias after previous myocardial infarction

OBJECTIVES The aim of this study was to estimate the value of QT dispersion measurement from the standard 12-lead electrocardiogram (ECG) in identifying patients susceptible to reentrant ventricular tachyarrhythmias after a previous myocardial infarction. BACKGROUND Variability in QT interval duration on the different leads of the 12-lead ECG has been proposed as an indicator of risk for ventricular arrhythmias in different clinical settings, but the value of QT dispersion measurement in identifying patients at risk for reentrant ventricular tachyarrhythmias after myocardial infarction is not known. METHODS The QT interval duration, QT dispersion and clinical and angiographic variables were compared between 30 healthy subjects; 40 patients with a previous myocardial infarction but no history of arrhythmic events or inducible ventricular tachycardia during programmed electrical stimulation; and 30 postinfarction patients with a history of cardiac arrest (n = 12) or sustained ventricular tachycardia (n = 18) and inducible, sustained monomorphic ventricular tachycardia by electrical stimulation. RESULTS Dispersion of the corrected QT interval (QTc) differed significantly between the study groups and was significantly increased in patients with susceptibility to ventricular tachyarrhythmias ([mean +/- SD] 104 +/- 41 ms) compared with that in both healthy subjects (38 +/- 14 ms, p < 0.001) and postinfarction patients with no susceptibility to arrhythmias (65 +/- 31 ms, p < 0.001). Maximal QT interval duration was also prolonged in the group with arrhythmias compared with that in the other groups (p < 0.001). Multivariate analysis, including clinical and angiographic variables, QT dispersion and maximal QT interval, showed that QT dispersion was the independent factor that most effectively identified the patient groups with and without susceptibility to ventricular tachyarrhythmias (p < 0.001). CONCLUSIONS Increased QT dispersion is related to susceptibility to reentrant ventricular tachyarrhythmias, independent of degree of left ventricular dysfunction or clinical characteristics of the patient, suggesting that the simple, noninvasive measurement of this interval from a standard 12-lead ECG makes a significant contribution to identifying patients at risk for life-threatening arrhythmias after a previous myocardial infarction.

Abnormalities in Beat-to-Beat Dynamics of Heart Rate Before the Spontaneous Onset of Life-Threatening Ventricular Tachyarrhythmias in Patients With Prior Myocardial Infarction

BACKGROUND Beat-to-beat analysis of RR intervals can reveal patterns of heart-rate dynamics, which are not easily detected by summary measures of heart-rate variability. This study was designed to test the hypothesis that alterations in RR-interval dynamics occur before the spontaneous onset of ventricular tachyarrhythmias (VT). METHODS AND RESULTS Ambulatory ECG recordings from 15 patients with prior myocardial infarction (MI) who had spontaneous episodes of sustained VT during the recording and VT inducible by programmed electrical stimulation (VT group) were analyzed by plotting each RR interval of a sinus beat as a function of the previous one (Poincaré plot). Poincaré plots were also generated for 30 post-MI patients who had no history of spontaneous VT events and no inducible VT (MI control subjects) and for 30 age-matched subjects without heart disease (normal control subjects). The MI control subjects and VT group were matched with respect to age and severity of underlying heart disease. All the healthy subjects and MI control subjects showed fan-shaped Poincaré plots characterized by an increased next-interval difference for long RR intervals relative to short ones. All the VT patients had abnormal plots: 9 with a complex pattern, 3 ball-shaped, and 3 torpedo-shaped. Quantitative analysis of the Poincare plots showed the SD of the long-term RR-interval variability (SD2) to be smaller in all VT patients (52+/-14 ms; range, 31 to 75 ms) than in MI control subjects (110+/-24 ms; range, 78 to 179 ms, P<.001) or the normal control subjects (123+/-38 ms, P<.001), but the SD of the instantaneous beat-to-beat variability (SD1) did not differ between the groups. The complex plots were caused by periods of alternating sinus intervals, resulting in an increased SD1/SD2 ratio in the VT group. This ratio increased during the 1-hour preceding the onset of 27 spontaneous VT episodes (0.43+/-0.20) compared with the 24-hour average ratio (0.33+/-0.19) (P<.01). CONCLUSIONS Reduced long-term RR-interval variability, associated with episodes of beta-to-beat sinus alternans, is a highly specific sign of a propensity for spontaneous onset of VT, suggesting that abnormal beat-to-beat heart-rate dynamics may reflect a transient electrical instability favoring the onset of VT in patients conditioned by structurally abnormal hearts.

Apolipoprotein E and B polymorphisms - longevity factors assessed in nonagenarians☆

To test if the prevalence of genetic risk factors for coronary heart disease (CHD) is low in individuals who have reached an extremely old age, the allele frequencies of apolipoprotein E (apo E) and B (apo B) polymorphisms and plasma lipoprotein(a) levels were investigated in nonagenarians and in younger control groups. The frequency of the epsilon 4 allele of apo E was significantly lower in the nonagenarians than in the middle-aged and young adults (P < 0.05). Also, the frequency of EcoRI allele R- of apo B was low in the nonagenarians, whereas the allele frequency for the XbaI polymorphism of apo B and plasma lipoprotein(a) concentrations did not differ between the nonagenarians and the younger groups. These findings strongly suggest that the presence of these potential genetic risk factors for CHD, namely the epsilon 4 allele of apo E and the R- allele of apo B, decreases the probability of an individual reaching an extremely old age.

Impaired low-frequency oscillations of heart rate in patients with prior acute myocardial infarction and life-threatening arrhythmias

Myocardial infarction results in abnormal cardiac autonomic function, which carries an increased risk of cardiac mortality, but it is not well known whether autonomic dysfunction itself predisposes patients to life-threatening arrhythmias or whether it merely reflects the severity of underlying ischemic heart disease. To determine the significance of abnormalities of cardiovascular neural regulation on the risk for ventricular tachycardia (VT), heart rate (HR) variability in the time and frequency domain were compared in a case-control study between 30 patients with a prior myocardial infarction and a history of sustained VT (n = 18) or cardiac arrest (n = 12) (VT group) and 30 patients with a prior myocardial infarction but no arrhythmic events (control group). The patient groups were carefully matched with respect to age, sex, location, ejection fraction, number of prior infarctions, number of diseased coronary arteries, and beta-blocking medication. In all patients in the VT group, inducibility into sustained VT was achieved, but none of the control patients had inducible nonsustained or sustained VT during programmed electrical stimulation. Patients in the VT group had a significantly lower SD of the RR intervals (p < 0.01), and reduced ultra low-, very low-, and low-frequency power spectral components of HR variability (p < 0.001 for all) than controls, but the high-frequency component of HR variability did not differ significantly between groups. In multiple regression analysis, reduced very low-frequency power of HR variability was the strongest independent predictor of VT susceptibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Association of lipoprotein cholesterol and triglycerides with the severity of coronary artery disease in men and women.

The differences between the lipid profiles of male and female patients and the effect of plasma lipids on the extent of coronary artery disease were evaluated in 122 angiographically assessed coronary artery disease patients (95 males and 27 females) and 60 controls. Both male and female patients had lower HDL-cholesterol and higher total cholesterol, LDL-cholesterol, triglyceride, VLDL-cholesterol and VLDL-triglyceride concentrations than the controls. The VLDL lipid values did not differ significantly between the male patients with different extent of CAD, whereas the VLDL lipid values of female patients tended to increase with an increasing severity of CAD. High Lp(a) (> or = 35 mg/dl) values were more prevalent in patients with > 50% coronary stenosis compared to patients with < 50% stenosis and the controls (29%, 17% and 12%, respectively). The apolipoprotein E phenotypes and epsilon allele frequencies were similar in the patients and the controls. Low HDL-cholesterol and high LDL-cholesterol are CAD risk factors for both sexes. For women, elevated VLDL-triglycerides seem to be an additional risk factor for CAD.

QT interval and arrhythmic risk assessment after myocardial infarction

To assess ventricular repolarization features as predictors of ventricular tachyarrhythmias (VT) in patients with previous myocardial infarction, we performed a dynamic study of QT interval from 24-hour electrocardiographic data. QT rate dependence was enhanced in patients with VT when compared with patients without VT.

Impaired negative chronotropic response to adenosine in patients with inappropriate sinus tachycardia

Adenosine and Inappropriate Sinus Tachycardia. Introduction: Adenosine is an endogenous nucleoside that has an important role in the diagnosis and treatment of several cardiac arrhythmias. However, its effects on inappropriate sinus tachycardia (IST) are not well established.

Asymptomatic coronary artery disease in diabetes: associated with autonomic neuropaphy?

To elucidate the potential association of diabetic autonomic neuropathy with increased prevalence of silent coronary artery disease (CAD), 138 asymptomatic diabetic subjects were screened using exercise ECG. 24-h ambulatory ECG and dynamic thallium scintigraphy. Fourteen patients with exercise-induced myocardial ischaemia and angiographically confirmed CAD (≥50% coronary artery narrowing) were found using this protocol. Their autonomic nervous function was assessed using standard cardiovascular tests and compared with that of 23 consecutive diabetic patients catheterised because of symptomatic CAD (mean New York Heart Association class 3.0). The diabetic patients with symptomatic CAD had more severe coronary atherosclerosis than the diabetic patients with asymptomatic CAD assessed by jeopardy score (P<0.01). The groups did not, however, differ with respect to autonomic function tests. Five patients (22%) with symptomatic CAD and 3 patients (21%) with asymptomatic CAD had definite autonomic dysfunction, i.e. two or more abnormal tests. Thus, our results suggest that the frequency of autonomic neuropathy is not increased in diabetic patients with asymptomatic CAD. The contribution of diabetic autonomic neuropathy to the absence of cardiac pain needs further clinical and pathological studies.

Standard 12‐Lead and 24‐Hour Ambulatory Electrocardiographic Abnormalities in Survivors of Tachyarrhythmic Cardiac Arrest

The aim of the present work was to compare the accuracies of variables obtained from a standard 12‐lead ECG and a 24‐hour ambulatory ECG in discriminating between patients with and patients without tachyarrhythmic cardiac arrest after a previous myocardial infarction.

Two-Dimensional Vector Analysis of Beat-to-Beat Dynamics of Ventricular Repolarization

Objective: Duration of ventricular repolarization is a result of complex interaction between autonomic modulation and heart rate (HR).