Coronary arterial remodeling studied by high-frequency epicardial echocardiography: an early compensatory mechanism in patients with obstructive coronary atherosclerosis.

Coronary arterial remodeling is a compensatory mechanism that may limit the adverse effects of coronary obstructive lesions by expansion of the entire vascular segment. To determine if this compensatory anatomic change occurs in patients, high-frequency epicardial echocardiography using a 12 MHz transducer was performed during open heart surgery in 33 patients (10 with normal coronary arteries undergoing valvular surgery and 23 with coronary atherosclerosis). From stop-frame videotape high-frequency epicardial echocardiographic images, cross-sectional measurements of luminal area and total arterial area (lumen, intima, media and dense adventitia) were made in the patients with atherosclerosis at the site of arterial lesions and from the most proximal portion of the same artery. Remodeling was defined as enlargement of the total arterial area. In normal arteries measurements were made from proximal and midarterial locations. In the patients with normal coronary arteries, total arterial area, as determined by high-frequency echocardiography, decreased from the proximal site to the midportion of the artery (from 10.4 +/- 0.9 to 8.4 +/- 1.0 mm2, p less than 0.05); luminal area also decreased (from 6.0 +/- 0.6 to 4.5 +/- 0.7 mm2, p less than 0.05). In patients with coronary arterial lesions, luminal area also decreased from the proximal site to the arterial lesion site (from 5.3 +/- 0.6 to 2.3 +/- 0.3 mm2, p less than 0.05), but total arterial area increased (from 11.6 +/- 1.0 to 13.0 +/- 1.0 mm2, p less than 0.05). Of the 25 coronary arteries evaluated, only 4 had angiographic evidence of coronary collateral formation. These data indicate that coronary arterial remodeling is an important compensatory mechanism in obstructive coronary disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Pediatric defibrillation: importance of paddle size in determining transthoracic impedance.

Transthoracic impedance is a major determinant of successful defibrillation or cardioversion, but no data are available concerning the range and determinants of transthoracic impedance in children. Transthoracic impedance was measured in ten ambulatory infants, 6 weeks to 9 months of age, and 37 children, 1.5 to 15 years of age, using a previously validated "test pulse" technique that measures transthoracic impedance without actually delivering a shock. We used hand-held "pediatric" (21 cm2) and "adult" (83 cm2) electrode paddles coated with either Redux paste or Redux creme. Transthoracic impedance in children was 108 +/- 24 omega (range 61 to 212 omega) using pediatric paddles. Using adult paddles lowered the transthoracic resistance by 47% to 57 +/- 11 omega (range 29 to 101 omega), P less than .05. In infants, transthoracic impedance (measured only with pediatric paddles) was 94 +/- 17 omega (range 74 to 124 omega). Using Redux paste as the coupling agent reduced transthoracic impedance by 13% (P less than .05). Transthoracic impedance was significantly but poorly related to body weight and body surface areas, but the correlations were not sufficiently high to be clinically useful. These data indicate that the larger adult electrode paddles will minimize transthoracic impedance and should be used when the child's thorax is large enough to permit electrode to chest contact over the entire paddle surface. This transition occurred at an approximate weight of 10 kg.

Factors affecting transthoracic impedance during electrical cardioversion.

Successful cardioversion is dependent on the delivery of sufficient current. Current is determined by energy and transthoracic impedance (TTI). Our purpose was to assess factors affecting TTI in humans. Twenty-eight patients undergoing elective cardioversion were monitored up to 48 hours after shock delivery. We also studied 10 normal subjects, who did not receive shocks, for comparison. TTI declined 8% in the first hour in patients who received shocks, but also 6% in the normal subjects who wore the same pads for 1 hour but received no shocks. Twenty-four hours later, TTI returned to baseline in the nonshocked subjects but remained reduced (93% of control, p less than 0.05) in the shocked patients. There was a correlation between the total energy delivered and the decline in TTI (r = 0.69). TTI was 9% lower at end-expiration than at end-inspiration (55 +/- 3 vs 50 +/- 3 ohms, mean +/- standard error of the mean, p less than 0.01, paired t test). In the normal subjects, when a nonsalt-containing coupling agent (ultrasound coupling gel) was compared with a salt-containing gel (Redux paste), TTI was 20% higher (65 +/- 5 vs 54 +/- 4 ohms, p less than 0.01) with the nonsalt-containing gel. When no coupling agent was used, TTI was markedly higher, 160 +/- 18 ohms (p less than 0.01 vs control). After 1 hour, TTI decreased 6% in the normal subjects when salt-containing gel was used, but did not change when a nonsalt gel was used.(ABSTRACT TRUNCATED AT 250 WORDS)

Can atherosclerotic coronary arteries vasodilate? An intraoperative high-frequency epicardial echocardiographic study.

Our purpose was to evaluate the vasodilating responses of atherosclerotic coronary arteries using intraoperative high-frequency (12 MHz) epicardial echocardiography. We obtained continuous high-frequency epicardial echocardiographic recordings during surgery, and determined cross-sectional lumen area from 17 coronary arterial segments (12 patients). Nitroglycerin (100 to 400 micrograms/min) was administered intravenously to reduce mean (+/- SEM) arterial pressure 14 +/- 1.8 mm Hg. The cross-sectional arterial images were classified using 3 different parameters: arterial lumen area, percentage of the arterial wall circumference that was atherosclerotic (wall thickness > 0.7 mm), and presence of an eccentrically shaped arterial lumen (maximal/minimal luminal diameter > 1.5). Nine arterial segments had small (< 5.0 mm2) arterial lumens (1.7 +/- 0.40 mm2 [+/- SEM; range 0.6 to 3.9]). With nitroglycerin, the luminal area increased 0.8 +/- 0.28 mm2 (range 0 to 2.5), and 39 +/- 12.1% (range 0 to 117). The remaining 8 segments had larger (> 5.0 mm2) lumens (8.7 +/- 0.91 mm2 [range 5.0 to 11.9]). With nitroglycerin the luminal area increased 4.3 +/- 1.11 mm2 (range 1.4 to 11.4), and 51 +/- 10.2% (range 16 to 96). Seven arterial segments had eccentric lumens; mean maximal/minimal ratio was 1.8 +/- 0.08 (range 1.6 to 2.0). The area increased 39 +/- 7.3% (range 16 to 71) with nitroglycerin. In the 10 concentrically shaped lumens (maximal/minimal lumen diameters 1.3 +/- 0.04 [range 1.1 to 1.5]), nitroglycerin increased luminal area by 48 +/- 12.6% (range 0 to 117) (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

What have we learned about coronary artery disease from high-frequency epicardial echocardiography?

We have used a high frequency epicardial echocardiographic technique to visualize and measure coronary artery lumens and walls in patients undergoing cardiac surgery. A 12 MHz probe (Surgiscan, Biosound Corp.) is sterilized and placed on the exposed epicardial coronary arteries. Transverse cross-sectional views are obtained from the arteries on the anterior surface of the heart: the right coronary artery to the cardiac margin and the left anterior descending coronary artery to the cardiac apex. Numerous echocardiographic-angiographic-pathological correlations have been obtained from this work. We have validated the echocardiographic lumen and wall measurements by comparing the echo measurements to histological material from pressure-distended coronary arterial segments (from animals and fresh human autopsy specimens). We have shown by comparison with angiography that coronary arteries which appear normal or only minimally diseased by angiograms are often diffusely and severely atherosclerotic. We have also evaluated the shape of atherosclerotic lesions and demonstrated a wide range of lumen shapes (oval, circular, complex) and location within the residual coronary lumen (eccentric vs. concentric). Highly eccentric lesions are characterized by relative preservation of portions of the arterial wall, and this may preserve vasoreactivity of the atherosclerotic vessel. We have also demonstrated remodeling of atherosclerotic lesions: enlargement of the total arterial area (wall plus lumen) as a compensatory mechanism to preserve the arterial lumen in the face of encroaching atherosclerosis. High frequency epicardial echocardiography offers an accurate, real-time, in-vivo method for the anatomic and functional evaluation of coronary atherosclerosis. This dynamic, in-vivo technique supports and extends information previously obtainable only from pathologic studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitization of reperfused myocardium to subsequent coronary flow reductions. An extension of the concept of myocardial stunning.

The purpose of the present study was to evaluate the response of briefly ischemic and reperfused myocardium to subsequent moderate reductions of coronary arterial flow. In mongrel dogs, a carotid to left anterior descending coronary shunt was constricted to produce moderate coronary flow reductions (50-60% of control) and to thereby reduce regional systolic thickening (measured by echocardiography or sonomicrometry). First, we demonstrated an abnormal response of reperfused myocardium to subsequent flow reductions. We performed two episodes of coronary shunt stenosis, with an intervening 5-minute complete coronary shunt occlusion followed by 30 minutes of reperfusion. In a control group, the same two shunt stenoses were done, but no intervening shunt occlusion was performed. In the control dogs, repeated coronary shunt stenosis that produced equivalent perfusion reductions also produced equivalent declines in regional wall thickening. In contrast, in the intervention group (animals undergoing the intervening occlusion-reperfusion sequence between two shunt stenoses), the second coronary shunt stenosis produced an exaggerated decline in regional systolic thickening, even though the decline in myocardial perfusion was similar to the first stenosis. Second, we sought to demonstrate the mechanism of the exaggerated decline of the reperfused myocardium to subsequent moderate flow reductions. Again, two groups of animals were studied. Each group underwent two episodes of coronary shunt stenosis with an intervening sequence of 5 minutes of complete shunt occlusion and 30 minutes of reperfusion. In addition, one of the groups received an infusion of the oxygen free radical scavengers superoxide dismutase and catalase during the occlusion-reperfusion sequence. In the superoxide dismutase and catalase-treated animals, the decline in regional systolic function during the postreperfusion shunt stenosis was similar to the preocclusion stenosis. Thus, oxygen free radical scavengers blocked the exaggerated contraction decline in response to the postreperfusion flow reduction. We conclude that briefly ischemic and reperfused myocardium displays an exaggerated response to subsequent coronary arterial flow reductions and that this response is a subtle manifestation of postischemic ventricular dyskinesis, or "stunning." The mechanism is probably oxygen free radical toxicity.

Cardiac evaluation of the patient with stroke.

Coronary artery disease and ischemic cerebrovascular disease are leading causes of morbidity and mortality in the United States. Coronary artery disease often coexists with asymptomatic carotid artery atherosclerosis, transient ischemic attacks, or ischemic stroke. Numerous studies have shown that mortality from all forms of ischemic cerebrovascular disease is primarily due to coronary artery disease. Thus, there is increasing interest in identifying coronary artery disease in patients with cerebrovascular disease, including those without clinical manifestations of heart disease. We review the use of current noninvasive techniques to detect coronary artery disease and present practical approaches to screen for ischemic heart disease. Current diagnostic imaging methods for potential cardioembolic sources of cerebral infarction are also discussed.

Mechanisms responsible for decline in transthoracic impedance after DC shocks.

To test the hypothesis that tissue hyperemia and edema in the current pathway cause a decrease in transthoracic impedance (TTI) following direct current (DC) shock, the thoracic-skin and skeletal blood flow and blood volume were measured in anesthetized dogs after three 100-J shocks. TTI declined 11% (P less than 0.01) after DC shocks. Blood flow increased 10-fold in skeletal muscle from 0.9 +/- 0.2 to 11.3 +/- 2.6 (SE) ml.100 g-1.min-1 (P less than 0.05). Blood flow did not change outside the current pathway. Blood volume increased in skin in the current pathway from 7.6 +/- 1.5 ml/100 g preshock to 17.5 +/- 2.0 ml/100 g (P less than 0.01) at 60 min after shock; skeletal muscle blood volume did not change. We also determined postshock tissue weight before and after 72 h of drying at 70 degrees C. The percentage decline from wet weight after drying was 68.4 +/- 3.4% in the current pathway vs. 64 +/- 3.8% outside the pathway (P less than 0.05), indicating the tissue in the current pathway was more edematous. Finally, hindlimb edema was induced by deliberate overperfusion. As hindlimb circumference (edema) increased, impedance declined. We conclude that increases in tissue blood flow or tissue blood volume or tissue edema contribute to the decline in transthoracic impedance after DC shock.

The role of intraoperative high-frequency epicardial echocardiography during coronary artery revascularization.

The intraoperative evaluation of the technical adequacy of coronary artery bypass graft anastomoses has been limited by a lack of suitable tools. To evaluate the role of intraoperative high-frequency epicardial echocardiography we examined 82 coronary artery bypass graft anastomoses in 29 patients shortly before or just after weaning from cardiopulmonary bypass. Minor defects that did not compromise the lumen of the anastomoses were seen in two patients. One major technical error, a near total occlusion of an internal mammary-to-coronary artery anastomosis, was not apparent on external inspection, but was clearly identified with high-frequency epicardial echocardiography. This was revised immediately. Thus, high-frequency epicardial echocardiography permits the intraoperative evaluation of coronary artery bypass graft anastomoses so that technical errors can be quickly identified and corrected.