Richard S. Meltzer

Intracardiac Thrombi and Systemic Embolization

Recent progress has been made in diagnosing and tracing the natural history of intracardiac thrombi by echocardiography. Left ventricular thrombi occur and cause emboli in three clinical conditions: acute myocardial infarction, left ventricular aneurysm as a sequel to infarction, and idiopathic dilated cardiomyopathy. Echocardiographic studies have shown that one third of patients with acute anterior myocardial infarction have left ventricular thrombi; only a small percentage of these patients have emboli. Administration of anticoagulants decreases the prevalence of left ventricular thrombi and the frequency of embolization in this group. Thrombi that are protruding and mobile are most likely to embolize. Anticoagulation treatment decreases the prevalence of embolization in idiopathic dilated cardiomyopathy and should be instituted regardless of whether atrial or ventricular thrombi are detected by two-dimensional echocardiography. In patients with chronic left ventricular aneurysm, thrombi occur commonly, but emboli, infrequently. Therefore, data are insufficient to suggest that anticoagulation treatment is indicated, even if left ventricular thrombi are detected by two-dimensional echocardiography.

Comparison of two-dimensional echocardiography with radionuclide angiography during hynamic exercise for the detection of coronary artery disease

Two-dimensional echocardiography (2DE) was performed during 30-degree left lateral decubitus bicycle exercise in 52 patients who underwent cardiac catheterization for suspected coronary artery disease (CAD). Adequate echocardiograms were obtained in 39 patients (75%). Thirty-five of these patients underwent radionuclide angiography (RNA) with the same exercise protocol as for echocardiography. Exercise-induced or increased initial asynergy was considered to be a positive test by both 2DE and RNA. Echocardiographic, scintigraphic, and coronary angiographic data were compared to each other. Significant CAD (greater than 50% luminal obstruction) was present in 26 patients (66%). One of 15 patients with exercise-induced asynergy by 2DE had no CAD. Six 2DE and two RNA studies during exercise were falsely negative, sensitivity 76% versus 91%. Inclusion of RNA ejection fraction data would increase the sensitivity but decrease the specificity of RNA. Exercise-induced septal asynergy was far more frequently present by 2DE than by RNA (11 versus 6) in the 17 patients who had exercise-induced anterior asynergy by both methods. We conclude that it was possible to perform exercise 2DE in 75% of our patients. Exercise-induced asynergy on 2DE was specific (92%) for CAD. The sensitivity of 2DE in detecting CAD was less than that of RNA.

TRANSMISSION OF ULTRASONIC CONTRAST THROUGH THE LUNGS

The pulmonary capillary bed normally removes echocardiographic contrast from the circulation, so contrast injected peripherally or on the right side of the heart is not seen on the left side of the heart in the absence of intracardiac or intrapulmonary shunts. Based on recent advances in the theoretic understanding of microbubble physiology, we propose several theoretic methods for causing the transmission of ultrasonic contrast through the lungs to enable opacification of the left side of the heart. Three of these methods are tested: (I) injection of ether, an organic compound which may pass the pulmonary capillaries in the liquid phase and cavitate in the pulmonary veins to yield left heart echo contrast, (2) injection of hydrogen peroxide, a substance which chemically decomposes on the left side of the heart to yield gaseous oxygen that can be imaged as echo contrast, and (3) injections of 5% dextrose in the pulmonary wedge position. The first two methods were tested in anesthetized pigs, and the third method in humans and anesthetized rabbits. All methods could cause transmission of echocardiographic contrast through the lungs. There were no adverse reactions in the human subjects. Pulmonary wedge injections in rabbits were associated with one large and three small myocardial infarctions out of 7 animals sacrificed 24 hr later. We conclude that transmission of echocardiographic contrast through a capillary bed is feasible though potentially dangerous.

Pulmonary wedge injections yielding left-sided echocardiographic contrast.

Ultrasound contrast on the left side of the heart without the need for left heart catheterisation was achieved by hand injections of 8 to 10 ml 5 per cent dextrose solution through a catheter in the pulmonary wedge position. Injections were performed in 18 patients undergoing routine cardiac catheterisation and M-mode or two-dimensional echocardiography was used. An adequate wedge position was attained in 17 of the 18 patients. Nine had injections through Cournand catheters, three through Swan-Ganz catheters, and five through both. In 11 of these 17 patients left atrial or left ventricular echocardiographic contrast was seen immediately after wedge injection. Two patients showed diminished or absent contrast on later injections from the same position. Better results were obtained with the Cournand catheter (11/15 positive) than with the Swan-Ganz (1/8 positive) catheter. Pulmonary artery injections proximal to the wedge position did not cause left-sided contrast. No complications were observed. The safety of this method remains to be determined.

Transmission of Echocardiographic Contrast Through the Lungs

At present echocardiographic contrast can only be obtained on the left side of the heart with the aid of direct left heart catheterization. Chapters 10 and 11 are devoted to the as yet experimental technique of causing left heart contrast by performing injections through catheters in the pulmonary wedge position, thus only necessitating right heart catheterization. Though this is preferable to left heart catheterization, the ability to create left heart contrast noninvasively (we include peripheral venous injections) would be still better.

Left ventricular function at similar heart rates during tachycardia induced by exercise and atrial pacing: an echocardiographic study.

M mode echocardiography was used in 10 normal subjects to study left ventricular dimension and function variables at identical heart rates during tachycardia induced by supine bicycle exercise or atrial pacing. Echocardiographic data were analysed independently by two observers. The maximum heart rate reached during atrial pacing was lower (mean (1SD) 148 (17) beats/min) than that reached during exercise (mean (1SD) 167 (14) beats/min). The left ventricular end diastolic dimension was greater before supine exercise than before atrial pacing, probably as a result of leg raising. At each graded exercise step the end diastolic dimension remained greater than during atrial pacing and the differences became progressively greater with increasing heart rates. The left ventricular end systolic dimension was not significantly different at each step during the two stresses. During recovery the end systolic dimension was significantly smaller after exercise than at corresponding heart rates induced by atrial pacing. Left ventricular function indices--fractional shortening and peak rates of left ventricular systolic and diastolic dimensional change--were significantly higher during exercise than during atrial pacing and the differences increased with heart rate. It is concluded that the intervention used to change heart rate has an important effect on M mode echocardiographic left ventricular dimensions; indices of left ventricular performance increase progressively during exercise and differ from those measured at the same heart rate during atrial pacing; it is important to consider heart rate, stroke volume, and loading conditions when reference values are used and when the effects of a particular stress are to be interpreted.

Contrast echocardiography in pulmonary hypertension: Observations explaining the early closure of the pulmonic valve

We studied pulmonary artery flow patterns in 11 patients with pulmonary hypertension and 11 normal volunteers, by means of peripheral intravenous injections of 5% dextrose solution during M-mode echocardiography. Most of the patients had moderate to severe pulmonary hypertension. All normal subjects had antegrade flow throughout systole until just prior to pulmonic valve closure; none of the patients with pulmonary hypertension had continued antegrade flow throughout systole. The seven with early closure of the pulmonic valve showed abnormal retrograde flow of contrast in mid- to late systole; this was never observed in normal subjects. We conclude that early closure of the pulmonic value is seen in patients with early systolic retrograde flow in the pulmonary artery. A hypothesis for the pathogenesis of this flow is presented. Contrast M-mode echocardiography is a valuable new tool for the study of flow characteristics over the pulmonic valve. In patients with poor quality pulmonic valve echograms during systole, retrograde flow during midsystole imaged by contrast echocardiography may substitute for early closure as a sign of pulmonary hypertension.

The Source of Echocardiographic Contrast

In the mid-1960s Joyner first noted ultrasonic contrast effect and he was acknowledged in the first publication on this subject by Gramiak et al. in 1968 [1]. Within a short time a similar contrast effect was noted using several different unrelated biologically compatible solutions, and it was suggested that the source of the contrast effect was microbubbles of air caused by cavitation at the catheter tip during injection [2–4]. Catheter tip cavitation had just been described in the radiologic literature [5]. The most important argument in favor of the microbubble origin of ultrasonic contrast was that its intensity decreased in water tank experiments when increased pressure was placed on the fluid. Such behavior would be expected of a bubble of air, but not of a solid or liquid ultrasonic reflector. However, this in vitro observation by no means proved that the contrast seen in vivo necessarily is made of microbubbles of gas — only that the microbubbles are one possible source. For example it has been suggested that the spontaneous contrast occasionally observed in patients with mitral prosthetic valves might be due to particulate matter such as platelets or fibrin or fine pieces of the cloth sewing ring of the prostheses [6]. We thus decided to study the source of ultrasonic contrast effect directly and performed the following studies [7, 8].

Left Ventricular Thrombus: Diagnosis, Anticoagulation, and Systemic Embolization

Within the past decade, it has been established that echocardiography can diagnose left ventricular thrombi with a fair degree of accuracy [1–11]. This has been an impetus to the performance of many studies on the natural history of these thrombi and their response to therapy. Unfortunately, the literature occasionally fails to differentiate between clinically different subgroups of patients. Left atrial and left ventricular thrombi are seen in different settings, and echocardiography is better in diagnosing ventricular than atrial thrombi. Three distinct clinical entities associated with the occurrence of left ventricular thrombi should be differentiated: acute myocardial infarction, chronic left ventricular aneurysm as a sequel to myocardial infarction, and idiopathic dilated cardiomyopathy in the absence of coronary disease. We review the accuracy of echocardiography for diagnosing intracardiac thrombi, and then discuss the role of echocardiography in the setting of acute myocardial infarction and chronic aneurysm in detecting thrombi, in predicting embolization, and in decisions about antithrombotic therapy.

Factors Affecting the Success of Attaining Left Heart Echo Contrast After Pulmonary Wedge Injections

Peripheral venous contrast echocardiography has become an important diagnostic method and finds increasing application for the detection of intracardiac right-to-left shunts [1–21] and tricuspid insufficiency [22, 23]. It has been established that microbubbles of air injected into the blood stream are responsible for the echo-cardiographic contrast effect [24, 25]. The pulmonary capillary bed acts as a filter for these microbubbles [26]. Thus, after a peripheral venous or right heart injection, the appearance of ultrasonic contrast in the left heart cavities proves the existence of an intracardiac of extracardiac right-to-left shunt.