Ming H. Hwang

Progression of native coronary artery disease at 10 years: insights from a randomized study of medical versus surgical therapy for angina.

Repeat coronary angiography was performed in 42 patients 10 years after randomization to medical (n = 21) or surgical (n = 21) therapy for chronic angina. The native coronary arteries were classified into 15 angiographic segments and 3 arterial trunks for analysis of progression of coronary artery disease. The incidence rate of disease progression in coronary segments was 24% and 28% in medically and surgically treated patients, respectively (p = NS). Grafted segments showed a 38% rate of disease progression, which was higher than the 18% rate of for nongrafted segments (p less than 0.001) and the overall rate of 24% for medically treated patients (p less than 0.01). Similarly, 29 (94%) of 31 grafted arteries exhibited disease progression compared with 19 (59%) of 32 nongrafted arteries (p less than 0.01) and 42 (67%) of 63 arteries in medically treated patients (p less than 0.01). In grafted vessels, disease progression occurred more often in arteries proximal (84%) to the anastomosis than in arteries distal (16%) to graft insertion (p less than 0.001). Progression occurred in 46% of proximal segments compared with 23% of distal segments (p less than 0.02). Progression was seen in 23 (55%) of 43 segments with an occluded graft compared with 30 (31%) of 96 segments with a patent graft (p less than 0.02). Ten years after randomization, medically and surgically treated patients showed a comparable rate of disease progression in coronary segments. However, surgical therapy appeared to significantly accelerate atherosclerotic progression in the grafted vessels, especially in the proximal portions. Occluded grafts also correlated with an adverse effect on disease progression.(ABSTRACT TRUNCATED AT 250 WORDS)

Progression of coronary artery disease after percutaneous transluminal coronary angioplasty

Thirty-nine patients underwent coronary arteriography 1 to 20 months (mean 7 months) after percutaneous transluminal coronary angioplasty (PTCA). At the time of the repeat study, 35 patients (90%) had recurrent angina or myocardial infarction, and 4 patients (10%) were asymptomatic. Restenosis, defined as greater than 50% loss of PTCA gained diameter, was found in 19 patients (49%). In addition, 20 patients had new lesions or marked progression of existing lesions (defined as greater than 20% or increasing greater than 20% obstruction in coronary diameter) in the previously normal or mildly diseased coronary segments. The new or progressive lesions occurred both in patients with restenosis at the PTCA site (nine of 19) and in patients without restenosis (11 of 20). New or progressive lesions tended to occur more commonly in the artery on which PTCA was performed (13 of 40) than in the artery that did not have PTCA (10 of 77) (p less than 0.02 by chi 2). In arteries that had PTCA, new or progressive lesions occurred more often in the segment proximal to the angioplasty site (seven of 13 or 54%) than in the peri-PTCA segment (two of 13 or 15%) and in the segments distal to it (four of 13 or 31%), but this observation did not reach statistical significance. No other clinical, angiographic, or PTCA procedure variables affected the occurrence of new or progressive lesions. In patients with recurrent angina or myocardial infarction after PTCA, both restenosis and new or progressive lesions are common. New lesions or marked progression of existing lesions tended to occur in the vessel subjected to PTCA.(ABSTRACT TRUNCATED AT 250 WORDS)

Contrast media-induced ventricular fibrillation. A comparison of Hypaque-76, Hexabrix, and Omnipaque.

Contrast media occasionally produce ventricular fibrillation during coronary angiography. We compared the fibrillatory propensity of the conventional ionic contrast medium, Hypaque-76 (H76) to the low osmolar ionic dimer Hexabrix (HB) and to the nonionic agent Omnipaque (OM) in 20 open chest anesthetized dogs. Intracoronary injection of 6 mL of contrast medium produced spontaneous ventricular fibrillation in four of ten dogs with H76, compared with two of ten with HB, and zero of ten with OM (P = .07). The induction of two premature beats by programmed stimulation of the myocardium during injection of 4 mL of contrast medium produced ventricular fibrillation in ten of ten dogs with H76, compared with three of ten with HB, and zero of ten with OM (P less than .001). Both H76 and HB produced ventricular fibrillation in ten of ten dogs when three premature beats were induced, compared with two of ten dogs with OM (P less than .001). Four mL H76 produced a 109 +/- 18 msec increase in the QT interval, compared with an 82 +/- 17 msec increase with HB, and a 45 +/- 12 msec increase with OM. We conclude that both low osmolar HB and OM are less fibrillatory than the conventional ionic medium H76, and that the nonionic medium OM is less fibrillatory than the ionic dimer contrast medium HB.

Effects of indomethacin on coronary hemodynamics, myocardial metabolism and anginal threshold in coronary artery disease

The effects of orally administered indomethacin or placebo on coronary hemodynamics were studied in 23 patients with coronary artery disease. After indomethacin administration the systemic arterial pressure increased by 12 +/- 4% and the myocardial oxygen consumption by 24 +/- 11%. Coronary sinus flow did not change and coronary vascular resistance increased slightly. Oxygen saturation of the arterial blood did not change, but coronary sinus saturation decreased substantially. Hemodynamic values returned to normal 150 minutes after administration of indomethacin. During rapid atrial pacing, coronary sinus flow increased 79 +/- 14% above the rest value when pacing was done before indomethacin administration; only a 56 +/- 12% increase was seen when pacing was repeated after indomethacin. Peak heart rate achieved during atrial pacing, severity of angina and the degree of ST-segment depression were not altered by indomethacin treatment. Orally administered indomethacin has a mild coronary vasoconstrictive effect that does not interfere substantially with the expected increase in myocardial blood flow during rapid atrial pacing. Anginal threshold is not altered by orally administered indomethacin.

The use of programmed electrical stimulation to assess the fibrillatory propensity of ionic and nonionic contrast media.

Coronary angiography occasionally results in ventricular fibrillation. To compare the fibrillatory propensity of conventional ionic and nonionic contrast media, we measured QT intervals and performed programmed electrical stimulation during intracoronary injection of Renografin 76 (R76), Hypaque 76 (H76), and iopamidol (IOP) in 16 open chest dogs. In ten dogs the incidence of ventricular fibrillation following induction of a single premature ventricular beat after every fourth atrial paced beat was 19/20 with R76, 8/20 with H76, and 0/20 with IOP (P less than .001). When two premature beats were induced, the incidence of ventricular fibrillation was 20/20 with R76, 19/20 with H76, and 1/20 with IOP (P less than .001). In six additional dogs, the mean prolongation of the QT interval was 170 +/- 20 msec with R76, 105 +/- 14 msec with H76, and 63 +/- 9 msec with IOP (P less than .001). Thus, programmed electrical stimulation readily induces ventricular fibrillation during intracoronary injection of conventional ionic contrast media. The incidence of ventricular fibrillation parallels the amount of QT interval prolongation produced. H76, which lacks EDTA and sodium citrate, is less fibrillatory than R76. However, the nonionic medium IOP appears far less fibrillatory than either R76 or H76.

Exercise induced “Mobitz type II” second degree AV block in a patient with chronic bifascicular block (right bundle branch block and left anterior hemiblock)

A 55 year old healthy man with chronic bifascicular block (right bundle branch block and left anterior hemiblock) had a near syncopal episode. A treadmill test showed exercise induced Mobitz type II AV block manifested clinically by paradoxical slowing of the heart rate and decreased blood pressure. True His Purkinje block and pseudo AV block due to His extrasystoles were documented by an electrophysiological study.

The effect of sodium on the fibrillatory propensity of nonionic contrast media.

Removing sodium from standard ionic contrast media markedly increases the incidence of ventricular fibrillation in patients undergoing coronary angiography. Newer nonionic contrast media, iopamidol, iohexol, and ioversol contain only trace amounts of sodium. To determine whether sodium attenuates or potentiates ventricular fibrillation from nonionic contrast media, we measured the prolongation in QT interval and performed programmed electrical stimulation with one, two and three extra ventricular stimuli in 40 dogs during 4-mL intracoronary injections of iopamidol, iohexol, and ioversol. Solutions of each contrast medium with added NaCl at concentrations of 0.225%, 0.45%, and 0.9% were compared with standard contrast media. The addition of NaCl markedly increased the amount of QT interval prolongation produced by each contrast medium. With iopamidol, the amount of QT interval prolongation was 40 +/- 11 msec with standard iopamidol, but was 58 +/- 11 msec with 0.225% NaCl/iopamidol, 84 +/- 17 msec with 0.45% NaCl/iopamidol, and 132 +/- 42 msec with 0.9% NaCl/iopamidol (P less than .001). Similar results were seen with iohexol and ioversol. Ventricular fibrillation was difficult to induce with standard solutions of these agents (even with three extra stimuli), but became progressively easier to induce when NaCl was added. Three extra stimuli produced ventricular fibrillation in zero of 11 dogs with standard iopamidol, zero of 11 with 0.225% NaCl/iopamidol, three of 11 with 0.45% NaCl/iopamidol, and eight of 11 with 0.9% NaCl/iopamidol (P less than .001). Similar results were observed with iohexol and ioversol. The addition of choline chloride or dextrose did not increase ventricular fibrillation and QT interval prolongation. It is concluded that standard preparations of nonionic contrast media have a very low fibrillatory propensity.(ABSTRACT TRUNCATED AT 250 WORDS)

Delayed Pulse Generator Malfunction after D.C. Countershock

Immediate pacemaker malfunction following defibrillation or cardioversion has been reported. In this paper we report one patient whose pacemaker appeared to be functioning normally after D.C, countershock but malfunctioned 13 days later manifested by changing from an R‐wave inhibited to an R‐wave synchronous mode.

The usefulness of dobutamine in the assessment of the severity of mitral stenosis

Patients with mitral stenosis often require supine exercise in order to increase their heart rate and cardiac output to assess the severity of their valvular obstruction during cardiac catheterization. We substituted dobutamine for exercise in 14 patients with suspected mitral stenosis. The dobutamine infusion was started at 5 micrograms/kg/min and was increased to 10, 15, and 20 micrograms/kg/min every 3 minutes as tolerated. The heart rate increased from 84 +/- 4 to 123 +/- 7 bpm (p less than 0.001), the cardiac index increased from 2.4 +/- 0.2 to 3.4 +/- 0.2 L/min/m2 (p less than 0.001), and the mean pulmonary artery pressure increased from 27 +/- 3 to 30 +/- 2 mm Hg (p less than 0.02). The pulmonary wedge pressure of 19 +/- 2 mm Hg and the mitral valve index of 0.8 +/- 0.1 cm2/m2 remained unchanged, but the left ventricular end-diastolic pressure decreased from 11 +/- 2 to 6 +/- 2 mm Hg (p less than 0.02). The hemodynamic response during the infusion of dobutamine identified a subgroup of patients with more severe mitral stenosis. Thus, the administration of dobutamine is useful in the evaluation of the severity of mitral valve obstruction during catheterization.

Effects of contrast media on coronary hemodynamics and myocardial metabolism.

RATIONALE AND OBJECTIVESThis study was designed to compare the effects of ionic contrast medium (CM), Renografin-76 (R76), and nonionic CM, Omnipaque-350 (OM350), on coronary hemodynamics and myocardial metabolism. METHODSIn 10 open-chest, atrial-paced dogs, 4 mL of R76 and OM350 were injected into the left anterior descending coronary artery. Coronary blood flow (CBF), myocardial oxygen consumption (MVO2), lactate extraction (LE), left ventricular (LV) dp/dt, and aortic systolic pressure (AOP) were measured. RESULTSThe maximal CBF changes caused by OM350 and R76 were 23.7 ± 3.3 mL/minute and 18.3 ± 3.3 mL/minute (NS), respectively. OM350 produced an increase in LV dp/dt by 378 ± 85 mm Hg/second, which was different from – 244 ± 65 mm Hg/second by R76 (P < .05). The changes in MVO2 and LE after OM350 injection were 2.6 ± 0.6 mL/minute and 10.2 ± 5 μM/minute, respectively; those were different from – 0.1 ± 0.4 mL/minute, and –7.7 ± 5.1 μM/minute after R76 injection (P < .05). CONCLUSIONAlthough both agents increased CBF, they appeared to act by different mechanisms. That a direct coronary vasodilator effect is the main action of R76 on coronary vascular response is suggested by decreasing myocardial contractility and oxygen consumption. However, OM350, by enhancing both parameters, may augment CBF at least in part by autoregulation.