Remote diagnosis of congenital heart disease in southern Arizona: comparison between tele-echocardiography and videotapes.

OBJECTIVE: We report our experience with tele-echocardiography and echocardiograms recorded digitally or on videotape (recorded-echos) at The University of Arizona from August 2006 to December 2010 and compare their quality and diagnostic accuracy. MATERIALS AND METHODS: Tele-echocardiograms (tele-echos) were transmitted from the Yuma Regional Medical Center to The University of Arizona via a T-1 and aT-3 line at a bandwidth of 768 kilobits per second. Recorded-echos were shipped for interpretation to The University of Arizona by overnight mail. Diagnostic accuracy was assessed by comparing tele- and recorded-echos with electrocardiograms performed by a pediatric cardiologist (PedsCard-echos). RESULTS: Three hundred forty-six tele-echos in 260 patients and 455 recorded-echos in 406 patients were performed (median age, 6 and 8 days, respectively). Indications included possible congenital heart disease (CHD), patent ductus arteriosus (PDA), and persistent pulmonary hypertension of the newborn. Diagnostic categories included complex CHD, non-critical disease, PDA, and other. PedsCard-echos were available for 27% of the tele-echo and 30% of the recorded-echo patients. Comparisons between tele- and PedsCard-echo yielded no discrepancies in 12 (23%), expected resolution of condition in 26 (49%), and minor in 14 (26%). One (2%) major discrepancy was detected. Comparisons between recorded- and PedsCard-echo showed no discrepancies in 28 (40%), expected resolution of condition in 14 (20%), and minor discrepancies in 28 (40%) patients. No significant difference with respect to discrepancies was detected between tele- and recorded-echos. There was significant (p<0.01) improvement in tele- and recorded-echo study quality by 2010. CONCLUSIONS: (1) Tele-echocardiography can be performed successfully with excellent accuracy. (2) The quality of tele- and recorded-echo studies improved toward the end of the analysis period. (3) Although initially tele-echo studies were more accurate than recorded-echo studies, there was no difference between these two types of studies by the fourth year of the study. (4) Both tele- and recorded-echos were indispensible in the remote diagnosis of CHD.

The influence of myocardial substrate on ventricular fibrillation waveform: a swine model of acute and postmyocardial infarction.

OBJECTIVE: In cardiac arrest resulting from ventricular fibrillation, the ventricular fibrillation waveform may be a clue to its duration and predict the likelihood of shock success. However, ventricular fibrillation occurs in different myocardial substrates such as ischemia, heart failure, and structurally normal hearts. We hypothesized that ventricular fibrillation is altered by myocardial infarction and varies from the acute to postmyocardial infarction periods. DESIGN: An animal intervention study was conducted with comparison to a control group. SETTING: This study took place in a university animal laboratory. SUBJECTS: Study subjects included 37 swine. INTERVENTIONS: Myocardial infarction was induced by occlusion of the midleft anterior descending artery. Ventricular fibrillation was induced in control swine, acute myocardial infarction swine, and in postmyocardial infarction swine after a 2-wk recovery period. MEASUREMENTS AND MAIN RESULTS: Ventricular fibrillation was recorded in 11 swine with acute myocardial infarction, ten postmyocardial infarction, and 16 controls. Frequency (mean, median, dominant, and bandwidth) and amplitude-related content (slope, slope-amp [slope divided by amplitude], and amplitude-spectrum area) were analyzed. Frequencies at 5 mins of ventricular fibrillation were altered in both acute myocardial infarction (p < .001 for all frequency characteristics) and postmyocardial infarction swine (p = .015 for mean, .002 for median, .002 for dominant frequency, and <.001 for bandwidth). At 5 mins, median frequency was highest in controls, 10.9 +/- .4 Hz; lowest in acute myocardial infarction, 8.4 +/- .5 Hz; and intermediate in postmyocardial infarction, 9.7 +/- .5 Hz (p < .001 for acute myocardial infarction and p = .002 for postmyocardial infarction compared with control). Slope and amplitude-spectrum area were similar among the three groups with a shallow decline after minute 2, whereas slope-amp remained significantly altered for acute myocardial infarction swine at 5 mins (p = .003). CONCLUSIONS: Ventricular fibrillation frequencies depend on myocardial substrate and evolve from the acute through healing phases of myocardial infarction. Amplitude related measures, however, are similar among these groups. It is unknown how defibrillation may be affected by relying on the ventricular fibrillation waveform without considering myocardial substrate.

Direction of signal recording affects waveform characteristics of ventricular fibrillation in humans undergoing defibrillation testing during ICD implantation.

INTRODUCTION: In cardiac arrest due to prolonged ventricular fibrillation (VF), defibrillation is more likely to result in a perfusing rhythm if chest compressions are performed first. Furthermore, the VF waveform can predict the shockability of VF and thus automated external defibrillators (AEDs) are being designed to analyze the VF waveform to direct therapies. However, it is unknown whether the VF waveform is dependent on recording direction, which could be altered by incorrect placement of AED patches. MATERIALS AND METHODS: VF was induced in 26 patients with ischemic cardiomyopathy and 19 patients with dilated cardiomyopathy and recorded in six limb leads. Frequency characteristics (mean, median, dominant frequency, and bandwidth) were computed as well as amplitude-based measures: amplitude spectral area (AMSA), slope, signal amplitude, and slope divide by signal amplitude (slope-amp). RESULTS: Frequency characteristics were similar in all leads. However, AMSA, slope, and signal amplitude were significantly affected (P<0.001) by lead. In particular, for ischemic cardiomyopathy patients, between leads I and II, AMSA varied from 29.4+/-3.2 to 49.3+/-4.6 mV Hz (mean+/-SEM, P<0.001) and slope varied from 1.5+/-0.2 to 2.4+/-0.3 mV/s (P<0.001). Slope-amp was similar in all leads. There were no significant differences between ischemic and dilated cardiomyopathy patients. CONCLUSIONS: Amplitude measures of VF are significantly affected by limb lead ECG recording direction. This work suggests that AED patches must be correctly and consistently placed if amplitude-based measures are used to decide whether to deliver a defibrillatory shock.

Ventricular fibrillation frequency characteristics are altered in acute myocardial infarction.

OBJECTIVE: Future automated external defibrillators are being designed to direct rescue efforts (chest compressions first vs. defibrillation) by inferring the duration of ventricular fibrillation based on its waveform characteristics such as frequency content. This approach assumes that the ventricular fibrillation waveform is an appropriate surrogate for ventricular fibrillation duration and is not affected by structural heart disease. We hypothesized that an acute myocardial infarction may alter the frequency content of ventricular fibrillation. DESIGN: Animal intervention study with comparison to control group. SETTING: University animal laboratory. SUBJECTS: Twenty-seven swine. INTERVENTIONS: Acute myocardial infarction was induced by occlusion of the mid-left anterior descending artery. Ventricular fibrillation was induced in swine with acute myocardial infarction and control swine. MEASUREMENTS AND MAIN RESULTS: Ventricular fibrillation was induced in 11 swine with an acute myocardial infarction and in 16 control swine. Ventricular fibrillation waveforms were analyzed for mean, median, and dominant frequency, as well as bandwidth and amplitude. All frequency characteristics were significantly (p < .001) altered in swine with acute myocardial infarction compared with controls. Specifically, these characteristics were significantly depressed and varied little over time in swine with acute myocardial infarction compared with controls. CONCLUSIONS: These data establish that ventricular fibrillation during an acute myocardial infarction has an altered frequency content and time evolution compared with ventricular fibrillation without coronary obstruction. Frequency characteristics such as mean, median, dominant, and bandwidth show little variation in time after an acute myocardial infarction and are not suitable surrogates for ventricular fibrillation duration. These findings have important implications for the development of "smart" automated external defibrillators designed to determine duration of ventricular fibrillation from the waveform characteristics.

Ventricular fibrillation waveform characteristics are different in ischemic heart failure compared with structurally normal hearts.

BACKGROUND: For prolonged VF, perfusion of the myocardium by pre-shock chest compressions can improve myocardial readiness for successful defibrillation. Characteristics of the VF waveform correlate with the duration of VF when there is no structural heart disease. A "smart" automated external defibrillator (AED) could therefore analyze the VF waveform, determine if VF has been prolonged, and then direct rescuers to either deliver a shock first or chest compressions first. We hypothesized that ischemic heart failure might alter the waveform content of ventricular fibrillation compared with normal hearts, complicating the determination of VF duration. METHODS: Myocardial infarction was induced by ligating the proximal left coronary artery. Six weeks later, VF was then induced in 10 rats with myocardial infarction and heart failure (MI-CHF) and 9 control rats. Waveforms were analyzed for total signal amplitude, median frequency, dominant frequency and bandwidth (the frequency interval containing 50% of the total amplitude about the median frequency). RESULTS: All of these VF waveform characteristics were altered substantially in MI-CHF rats compared to normal controls. In particular, MI-CHF rats had decreased signal amplitude early in VF (p=0.02), a broader bandwidth (p=0.001) and different frequency characteristics over time (p<0.001). CONCLUSIONS: VF waveforms vary over time in a typical manner among rats with and without ischemic heart failure. However, the time-course and waveform characteristics of ventricular fibrillation are altered in rats with myocardial infarctions and ischemic heart failure compared to normal controls. These findings have important implications regarding the use of waveform analyses to determine the duration of VF.

Ventricular fibrillation frequency characteristics and time evolution in piglets: a developmental study.

BACKGROUND: Derived variables of ventricular fibrillation, such as the frequency distribution by fast Fourier transformation and its evolution over time, have been used to determine the optimum timing for defibrillation. We hypothesized that these frequency variables would differ among neonatal, young child and older child populations due to cardiac developmental and size differences. Such differences may have important implications for developing defibrillation algorithms for pediatric patients and for extrapolating adult defibrillation algorithms to children in VF. METHODS: Ventricular fibrillation was induced and recorded for 6 min in 4 kg (n = 11), 14 kg (n = 10), and 24 kg (n = 16) piglets, corresponding to neonatal, young child and older children. Mean, median, and dominant frequencies were computed in 30 s intervals and compared among weight classes. RESULTS: All frequency variables in all weight groups showed first a decline at 1.25-1.75 min, followed by a gradual rise and plateau. There were significant differences for mean, median and dominant frequencies among weight classes. Specifically, 14 kg piglets showed higher frequency variables overall with a time evolution that was different from that of 4 and 24 kg piglets. Mean frequency showed the most stable time evolution with the least moment-to-moment variability. CONCLUSION: The frequency waveform characteristics and time course are somewhat different in 14 kg piglets compared with 4 and 24 kg piglets. If similar differences are demonstrable among children of different weights and ages, AEDs designed to determine optimal timing of defibrillation shocks in adults by frequency waveform characteristics may require modification for use in children with VF.

Acute cardiac effects of nicotine in healthy young adults.

BACKGROUND: Nicotine is known to have many physiologic effects. The influence of nicotine delivered in chewing gum upon cardiac hemodynamics and conduction has not been well-characterized. METHODS: We studied the effects of nicotine in nonsmoking adults (6 male, 5 female; ages 23-36 years) using a double-blind, randomized, cross-over study. Subjects chewed nicotine gum (4 mg) or placebo. After 20 minutes (approximate time to peak nicotine levels), echocardiograms and signal-averaged electrocardiograms (SAECG) were obtained. After 40 minutes, subjects were again given nicotine gum or placebo in cross-over fashion. Standard echocardiographic measurements were made from two-dimensional images. We then calculated end-systolic wall stress (ESWS), shortening fraction (SF), systemic vascular resistance (SVR), velocity for circumferential fiber shortening corrected for heart rate (Vcfc), stroke volume, and cardiac output. P wave and QRS duration were measured from SAECG. RESULTS: Significant differences (P < 0.05) from control or placebo were found for ESWS, mean blood pressure, cardiac output, SVR, heart rate, and P wave duration. No significant changes were seen in left ventricular ejection time (LVET), LV dimensions, SF, contractility (Vcfc), or QRS duration. CONCLUSIONS: These results suggest that nicotine chewing gum increases afterload and cardiac output. Cardiac contractility does not change acutely in response to nicotine gum. Heart rate and P wave duration are increased by chewing nicotine gum.