H.Dieter Ambos

Effects of dobutamine in patients with acute myocardial infarction

This study was designed to evaluate the effects of dobutamine, a new cardioselective beta adrenergic agonist, on cardiac performance and myocardial injury in patients with evolving myocardial infarction. Results in 16 patients given dobutamine (1 to 40 microng/kg per min for 24 hours) were compared with those in two groups of control patients: one of 16 patients matched for predicted infarct size, and the other of 16 patients matched for early ventricular dysrhythmia, analyzed by computer. Infarct size was predicted from plasma creatine kinase (CK) values during the first 7 hours after the initial elevation, before infusion of dobutamine. Overall observed infarct size was estimated from hourly CK values for 48 hours (including those before and after administration of dobutamine). In all patients technetium-99m (stannous) pyrophosphate scans were positive for myocardial infarction. Dobutamine increased cardiac output (assessed by thermodilution) from 4.9 +/- 0.37 (mean +/- standard error) to 6.0 +/- 0.38 liters/min (P less than 0.05) and decreased pulmonary arterial occlusive pressure from 21.5 +/- 2.7 to 16.7 +/- 1.6 mmHg (P less than 0.01) without significantly altering heart rate or systemic arterial blood pressure. The ratio of observed to predicted infarct size, the frequency of independently detected reinfarction or extension of infarction and the frequency of premature ventricular complexes were similar in control and treated patients. Thus administration of dobutamine in doses sufficient to improve ventricular performance after myocardial infarction does not exacerbate myocardial injury or ventricular dysrhythmia.

Radiation Exposure to Patients and Medical Personnel During Radiofrequency Catheter Ablation for Supraventricular Tachycardia

Radiofrequency catheter ablation is an effective alternative to medical therapy for patients with supraventricular arrhythmias. The purpose of this study was to determine the risks to the patient and to medical personnel due to radiation exposure from fluoroscopy during radiofrequency ablation of supraventricular tachycardia. One hundred eight consecutive patients with Wolff-Parkinson-White syndrome or atrioventricular nodal reentry who underwent the ablation procedure were studied. The ablation procedure was successful in 95% of the patients studied. Preexcitation or supraventricular tachycardia recurred in 5% of the patients during a mean follow-up of 9 +/- 4 months. The mean fluoroscopy time was 50 +/- 31 minutes. An anthropomorphic radiologic phantom was used to determine organ exposure and the effective dose equivalents for the patient and medical personnel. The patients effective dose equivalent during a representative ablation procedure was 1.7 rems, which is comparable to other invasive cardiovascular procedures. The risk of inducing a fatal cancer from this exposure is 1 chance in 745, which is 1% of the spontaneous risk. The risk of a serious birth defect is 1 chance in 80,000, which is 0.1% of the current incidence of serious birth defects in the United States. The cardiologist who receives the highest exposure among medical personnel, would incur 1.8 mrems per case or 450 mrems per year if 250 procedures were performed. This exposure is 9% of the recommended annual limit. These results demonstrate the efficacy of radiofrequency energy ablation of supraventricular tachycardia and confirm that radiation exposure to patients and medical personnel is within established guidelines.

Quantification of differences in frequency content of signal-averaged electrocardiograms in patients with compared to those without sustained ventricular tachycardia☆

To quantify differences in the frequency content of signal-averaged electrocardiograms between patients with and without sustained ventricular tachycardia (VT), the energy spectra of the terminal QRS and ST segments of signal-averaged orthogonal ECGs were computed in 3 groups of patients by squaring the magnitude of the fast-Fourier transformed data. The terminal 40 ms of the QRS complex and ST segment were analyzed as a single unit to enhance frequency resolution. Group I comprised 23 patients with documented, remote myocardial infarction who had manifested subsequent episodes of sustained VT; group II comprised 53 patients with previous, remote infarction without subsequent sustained VT; and group III comprised 11 normal subjects. The terminal QRS and ST segments from patients with sustained VT contained a 10- to 100-fold greater proportion of components in the 20- to 50-Hz range compared with corresponding electrocardiographic segments in patients without VT. There were no significant differences in the peak frequencies among patient groups. However, the relative contribution of the magnitudes of these peak frequencies to the overall maximum magnitude of the spectral plot differed significantly (p less than 0.0001). No frequencies above 50 Hz contributed substantially to the energy spectra of the terminal QRS and ST segments in any group. Thus, differences in the energy spectra do not result from differences in the frequencies of components, but are attributable instead to differences in the amplitudes of components within a relatively narrow range of frequencies. The quantitative approach developed should provide objective indexes for assessing effects of antiarrhythmic interventions on abnormalities recognizable by frequency-domain analysis and improve noninvasive definition of risk for development of sustained VT.

Detection of premature ventricular contractions with a clinical system for monitoring electrocardiographic rhythms

Abstract An evaluation was made of the performance of an on-line computer system for the detection of premature ventricular contractions. Following a rigidly defined protocol, 34 patients having an average PVC rate of almost one out of every twelve beats were studied, and approximately fifty thousand beats were analyzed independently by human observer and correlated with computer analysis. In the population studied, 78% of the PVCs were detected accurately. In addition, no patient was encountered having a PVC which was always missed by the computer. No false positive PVCs occurred in half the cases, and in 31 cases, only 39 computer labeled “PVCs” could be clearly called false positive PVCs based on information in the single-lead electrocardiogram. The patients studied had a variety of different rhythm complications including atrial fibrillation and premature ventricular contractions from multiple foci. The factors affecting performance were analyzed and directions for future improvement discussed.

Improved differentiation of patients with and without ventricular tachycardia by frequency analysis of multiple electrocardiographic leads

Previously, these investigators have analyzed fast Fourier transforms of signal-averaged electrocardiograms (ECGs) to distinguish patients with from those without sustained ventricular tachycardia (VT). In these studies, analysis was performed on X, Y and Z ECG signals and patient to patient comparisons were based on an average of the X, Y and Z results. The purpose of this study was to determine the extent to which fast Fourier transform analysis of individual ECG leads and of the vector magnitude contribute to the differentiation of patient groups. Studies were performed in 28 normal subjects (group I), 38 patients with prior myocardial infarction but without VT (group II), 38 patients with anterior infarction and sustained VT (group III) and 29 patients with inferior infarction and sustained VT (group IV). Results in group I were used to define normal values for the area and peak magnitude ratios for the individual X, Y and Z leads and for the vector magnitude and to define normal values for the mean XYZ area and peak magnitude ratios. Spectra of the X, Y and Z leads, the vector magnitude and the mean XYZ results were significantly different in patients with VT compared with normal subjects and patients without VT (p less than 0.001). Results were abnormal in multiple leads from 71% of patients with VT and from only 5% of normal subjects (p less than 0.0001). In many patients with VT, abnormalities were identified in 2 of the 3 leads indicating a selective spatial distribution of altered ECG signals that elicit abnormal frequency components.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of infarct size with MB rather than total CK

We estimated infarct size in 95 patients with clinically uncomplicated infarction from total CK and results were compared to infarct size index based on plasma MB CK. Among patients with relatively low infarct size index indicative of relatively small infarctions (less than or equal to 20), estimates with total CK correlated closely with those based on MB CK (r = 0.88). In contrast, among patients with larger infarcts (infarct size index greater than 20) the correlation was poor. In this group, values for infarct size index based on total CK were 67 +/- 4 (SE)% greater than those based on MB CK. In the overall population, infarct size index based on MB (14 +/- 1 (SE) CK-gram-equivalents/m2) was less than that based on total CK (21 +/- 2). These disparities appear to reflect occult release of non-cardiac CK in patients with more extensive infarction. Thus, even in patients without overt clinical complications enzymatic estimates of infarct size are more accurate when based on MB rather than total plasma CK.

Initiation of repetitive ventricular depolarizations by relatively late premature complexes in patients with acute myocardial infarction

Abstract To determine whether repetitive ventricular depolarizations are more commonly precipitated by early compared with late premature ventricular complexes, we analyzed continuous electrocardiographic recordings obtained during the first 10 hours in 38 patients with myocardial Infarction without shock with the Argus/H computer system with editor verification of all premature ventricular complexes. Episodes of repetitive ventricular depolarization were defined as two or more consecutive complexes at a rate of 120 beats/min or greater. Premature ventricular complexes occurring with coupling intervals from the preceding normal complex equal to or less than the Q-T interval of the normal complex were defined as early, and those with longer coupling intervals as late. Among all premature ventricular complexes, early premature ventricular complexes accounted for 38 percent. The average coupling interval of premature ventricular complexes from a preceding normal complex did not correlate with heart rate, blood pressure, infarct size estimated enzymatically, the electrocardiographic locus of Infarction or history of previous Infarction. Twenty-nine patients had a total of 337 episodes of repetitive ventricular depolarizations. Somewhat surprisingly, 78 percent of these episodes, and all episodes in 22 patients, were initiated by late premature ventricular complexes. Thus, repetitive ventricular depolarizations in patients with acute myocardial infarction are often precipitated by late rather than early premature ventricular complexes.

Noninvasive detection of patients with ischemic and nonischemic heart disease prone to ventricular fibrillation

Abnormalities in the fast Fourier transforms of signal-averaged electrocardiograms (ECGs) obtained during sinus rhythm appear to distinguish patients with ischemic heart disease and sustained monomorphic ventricular tachycardia from those without ventricular tachycardia. This study was performed to determine the power of frequency analysis to detect patients with a history of ventricular fibrillation, to determine the extent to which spectra of signal-averaged ECGs from patients with ischemic and nonischemic heart disease are comparable and to compare results of signal-averaged ECG analysis in patients with ventricular fibrillation with results of programmed ventricular stimulation. Signal-averaged ECGs were obtained during sinus rhythm from 60 patients with sustained ventricular tachycardia (Group I) and 34 patients with ventricular fibrillation (Group II). Results of signal-averaged ECG analysis were abnormal in 92% of patients with ventricular tachycardia and 85% of patients with ventricular fibrillation (p = NS). Abnormal spectra were detected in the signal-averaged ECGs from 90% of patients with ischemic and from 86% of patients with nonischemic heart disease (p = NS). In contrast, the results of programmed stimulation differed markedly between the two patient groups. Sustained ventricular arrhythmias were induced in 91% of the patients with ventricular tachycardia compared with only 46% of those with ventricular fibrillation (p less than 0.0001). Moreover, ventricular tachycardia was inducible in 81% of patients with ischemic heart disease compared with only 50% of those with nonischemic heart disease (p less than 0.02). Thus, abnormalities in the spectra of signal-averaged ECGs were found in the majority of patients with ventricular fibrillation and were detectable even in those whose arrhythmia was not inducible by programmed stimulation. These results broaden the potential clinical application of noninvasive interrogation of signal-averaged ECGs to include the prospective identification of patients with ischemic or nonischemic heart disease prone to ventricular tachycardia or ventricular fibrillation.

Enzymatic estimation of myocardial infarct size when early creatine kinase values are not available.

Estimates of myocardial infarct (MI) size based on plasma creatine kinase (CK) are used widely for prognosis and in the assessment of therapy designed to salvage ischemic myocardium. However, if the initial plasma CK activity is elevated, MI size will be underestimated. To determine the impact of loss of early CK values on estimates of MI size and to develop a procedure to compensate for it, estimates of MI size based on complete and incomplete MB and total CK time-activity curves from 120 patients (experimental group) were compared. Estimates of MI size based on data inclusion intervals beginning at 24, 12, 8, and 4 hours before peak CK were 11, 14, 23, and 47% smaller than values based on complete CK curves, but the correlation was good between complete and incomplete estimates of MI size at any given interval, with r values ranging from 0.91 to 0.98. The derived correction factors were then prospectively applied to a new population (n = 25) with complete CK curves to compensate for purposely omitted early CK values. The corrected estimates of MI size were within 7% of those based on the complete CK curves. Similar results were obtained for transmural and nontransmural and anterior or inferior MI. Thus, if peak plasma CK is known, underestimation of MI size can be compensated for despite the unavailability of early CK values. Since greater than 90% of patients present before plasma CK has reached its peak (24 hours), MI size can be obtained in nearly all patients. Thus, being able to correct for unavailable early CK values makes MI size a more widely applicable endpoint for use in clinical trials and patient management.

Prospective detection of vulnerability to sustained ventricular tachycardia in patients awaiting cardiac transplantation

This prospective study tested the hypothesis that abnormal signal-averaged electrocardiograms (ECGs) and inducible ventricular arrhythmias identify patients awaiting cardiac transplantation who are prone to sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Thirty-seven patients with advanced symptoms of heart failure and a mean left ventricular ejection fraction of 20 +/- 7 were studied. In response to programmed ventricular stimulation using up to 3 extrastimuli, sustained monomorphic VT was induced in 8 (22%) and polymorphic VT or VF was induced in 5 patients (13%). Patients with inducible arrhythmias underwent drug therapy guided by results of programmed ventricular stimulation or implantation of a defibrillator. Patients in whom ventricular arrhythmias could not be induced were not treated for arrhythmias. The signal-averaged ECG was abnormal and sustained VT or VF was induced in 10 patients (27%). Follow-up ranged from 1 to 33 months (mean 12). Four patients (11%) died suddenly and 4 (11%) had nonfatal sustained VT or VF. The positive predictive value for sudden death or nonfatal VT/VF was 27% for the signal-averaged ECG, 38% for programmed ventricular stimulation, and 50% if both tests were abnormal. The negative predictive values for these tests were 87, 88 and 88%, respectively. The actuarial incidence of arrhythmic events was significantly higher in patients with inducible ventricular arrhythmias (p = 0.017) and in patients in whom both the results of signal-averaged electrocardiographic analysis and the response to programmed ventricular stimulation were abnormal (p = 0.002). This study demonstrates that results of signal-averaged electrocardiographic analysis and the response to programmed ventricular stimulation improve risk stratification for sudden cardiac death in patients awaiting cardiac transplantation.