The mechanism of production of ventricular fibrillation in coronary angiography

Cerebral angiography using transauricular access in a rabbit model: a new technique

BACKGROUND

Cerebral angiography in a rabbit model is widely used in the field of interventional radiology. Conventionally, the femoral artery is used for cerebral angiography in radiology departments. However, angiographic studies require surgical cutdown of the femoral artery, which is technically difficult.

PURPOSE

To evaluate a new cerebral angiography technique involving a transauricular approach in a rabbit model.

MATERIAL AND METHODS

In each of 10 rabbits, central auricular arteries were punctured in the right or left ear with a 20-gauge i.v. catheter. A microcatheter (2.0 F) with a 0.016-inch guide wire was introduced through the i.v. catheter and advanced to the aortic arch. The microcatheter and guide wire were advanced selectively into cerebral arteries and angiography was performed.

RESULTS

Central auricular arteries were successfully punctured with 20-gauge i.v. catheters. After approaching the aortic arch, microcatheter tips and guide wires were advanced manually to cerebral arteries on both sides. Difficulties in selecting the carotid arteries were resolved by using a looping technique within the cardiac chamber. Microcatheter loops within the cardiac chamber disappeared or remained during artery superselection.

CONCLUSION

Transauricular cerebral angiography appears to be a feasible technique for brain or carotid intervention studies in rabbits. In addition, vertebral angiography using a transauricular approach is possible using the looping technique. Selection of carotid or vertebral arteries on each side was not difficult when the microcatheter and guide wire were looped within the cardiac chamber. The ear chosen for the initial puncture does not appear to be important.

Reduction of the Risk of Ventricular Fibrillation in the Isolated Rabbit Heart by Small Additions of Electrolytes to Non-Ionic Monomeric Contrast Media

Perfusion of the isolated rabbit heart with solutions (350 mg I/ml) of the non-ionic contrast media iohexol and iopentol, both containing NaCl (20 mmol/l), caused a significantly lower frequency of ventricular fibrillation (VF) than solutions without NaCl. Iohexol or iopentol with NaCl (10 mmol/l) caused an intermediate frequency of VF. Iohexol with 10 or 20 mmol NaCl/l caused about the same frequency of VF as iohexol solutions with about the same total electrolyte concentration but with electrolyte composition as that of Krebs' solution. At 320 mg I/ml, solutions of iohexol (20 mmol NaCl/l), iodixanol (20 mmol NaCl/l) and ioxaglate (155 mmol Na/l) all produced a significantly lower frequency of VF than iohexol without NaCl. Ioxaglate caused the largest and iodixanol the smallest decrease in contractile force of the media. The investigation suggests that the small risk of VF from non-ionic monomeric media can be further reduced by adding a small amount of sodium chloride or of the electrolytes of Krebs' solution.

Cardiac Effects of Adding Electrolytes and Oxygen to Iohexol in a Dog Model of Contrast Media-Induced Ventricular Fibrillation

We investigated whether addition of a balanced electrolyte supplement and oxygen to the nonionic contrast medium iohexol reduces the risk of ventricular fibrillation (VF), and studied regional electrophysiology prior to the VF event. Twenty ml of each test solution were infused at a rate of 0.5 ml/s into the left anterior descending coronary artery (LAD) in 8 anesthetized dogs. LAD was externally occluded during infusion, to simulate a wedged catheter situation. ECG, hemodynamics, regional epicardial monophasic action potential duration (MAPD) and ventricular activation times (VAT) were calculated. All infusions with iohexol caused VF within 27 s. Five of 12 infusions with iohexol + 30 mmol NaCl, 3 of 11 infusions with iohexol + electrolytes (IPE) (NaCl, KCl, CaCl2 and MgCl2) and 4 of 11 infusions with IPE with oxygen addition (IPE + O2) caused VF after 45 s. Iohexol did not change MAPD prior to the VF event. Iohexol + 30 mmol NaCl and the IPE solutions lengthened MAPD initially, but at the time of the VF event MAPD were normalized or shortened. We conclude that electrolyte supplement to iohexol may prevent VF, probably by lengthening MAPD.

Addition of Sodium to Iohexol

The addition of sodium to nonionic contrast media has reduced the incidence of arrhythmias in animal models. The influence on cardiac function and safety of sodium addition to the nonionic contrast medium iohexol (Omnipaque) was studied in a randomized, double-blind trial in patients undergoing cardioangiography. Fifty-nine patients received iohexol 350 mg I/ml with NaCl 28 mmol/l and 58, iohexol only. ECG changes after contrast injections were evaluated with continuous computerized dynamic vectorcardiography (VCG). QRS-vector difference (QRS-vd), which reflects changes in the QRS-complex, was chosen as the main parameter. Both contrast media caused changes in the QRS-complex, but there was no significant difference between the two. No serious arrhythmias were observed. Both contrast media were well tolerated. No beneficial effects from enriching iohexol with sodium were found. VCG was found to be a valuable tool in the study of contrast medium-induced ECG changes.

Effect of Sodium Addition to Non-Ionic Contrast Media on Cardiac Contractile Force

Cardiac contractile force after adding NaCl to the non-ionic contrast media iohexol and iopentol was investigated in the isolated rabbit heart. Iodine concentrations of 150, 300 and 350 mg I/ml were used with sodium concentrations ranging from 0 to 154 mmol/l. From physiologic experiences of nutrient solutions it should follow that a sodium-free solution of a non-ionic contrast medium, which also has the lowest hypertonicity, should cause the smallest decrease in contractile force. However, a small amount of sodium added to the contrast medium solutions, in the range of 19.25 to 38.5 mmol/l, caused the least decrease in contractile force. The decrease in contractile force was significantly more pronounced when no sodium was added or when larger amounts of sodium were added. A small amount of sodium also decreases the risk of ventricular fibrillation. Thus there is a possibility that addition of sodium could reduce the adverse effects of cardioangiography.

Effects of Contrast Media on the RR and QT Interval during Coronary Arteriography

During coronary arteriography, transient prolongation of the RR and QT intervals can be observed to occur. Animal experiments have suggested that low-osmolality contrast media have less effect, but there have been few clinical studies of this phenomenon. We analyzed 95 electrocardiographic records from patients who had undergone coronary arteriography and assessed the maximal prolongation of the RR and QT intervals. The contrast media used for arteriography included meglumine sodium diatrizoate, iopamidol, iohexol, and meglumine sodium ioxaglate. Diatrizoate caused the greatest electrocardiographic changes. Among the low osmolality contrast media, ioxaglate caused the smallest bradycardial effect and iohexol the smallest prolongation of the QT interval. It appears necessary to consider some additional factors for osmolality or ionicity, such as the chemotoxicity of the chemical structure of the iodinated contrast medium moiety, when assessing their potential adverse effect on the cardiac conduction system.

Reducing arrhythmogenic effects in the isolated heart enriching roentgen contrast media with electrolytes. Survey and present state

A review of the literature on the effects of adding electrolytes to ionic as well as nonionic contrast media (CM) in the isolated heart model reveals that both ionic and nonionic CM favor from such addtion, if the added electrolytes are balanced with respect to each other. By enriching nonionic monomeric as well as dimeric CM with such a balanced electrolyte solution, the risk of ventricular fibrillation is reduced and myocardial contractibility is improved compared to nonionic CM without such enrichment. The new nonionic dimer iodixanol is slightly hypotonic to plasma in concentrations suitable for coronary arteriography. The water solution of iodixanol therefore contains an osmotic space in which electrolytes can be added, therby making it isotonic with plasma.

Cardioangiography and the hemodynamic effects of iodixanol

Patient safety should be in focus when using contrast media (CM) in diagnostic and interventional cardiac procedures. Side-effects that occur during cardioangiography due to hemodynamic effects of CM include direct effects on the heart, effects on the systemic and pulmonary circulation, and effects on the blood volume. Although not a totally inert solution, iodixanol (Visipaque) has less pronounced direct inotropic effects on the heart than have other CM; its vasodilatory effects on peripheral arteries are smaller, and the increase in blood volume is smaller after administering iodixanol than after other CM. Thus, iodixanol represents a further step forward in terms of reducing side-effects during contrast-enhanced diagnostic and interventional cardiac procedures.

Cardiac electrophysiology, arrhythmogenic mechanisms and roentgen contrast media

Contrast media (CM) affect normal cardiac electrophysiology when injected into the coronary arteries. High-osmolality CM cause more pronounced electrophysiological effects than do low-osmolality CM. Further, both high- and low-osmolality ionic CM have more pronounced effects than the nonionic CM. The CM-induced electrophysiological effects involve regional disturbances of depolarization and repolarization, thereby causing disturbances of impulse conduction as well as dispersion of refractoriness. Recent experimental studies have demonstrated that the addition of sodium or a balanced electrolyte supplement to nonionic CM reduces the risk of ventricular fibrillation (VF), particularly when the CM is injected in a wedged catheter situation. The reduced risk of VF may be due to the small and transient lengthening of repolarization seen in the CM-perfused area of the myocardium. Iodixanol, which is an isotonic nonionic dimer supplemented with NaCl and CaCl(2), is as well tolerated as iohexol during free coronary flow. However, when flow is restricted, such as when CM is injected through a wedged catheter, the risk of VF is less with iodixanol than with iopamidol, iohexol and ioxaglate.

A review of coronary arteriography- and contrast media-induced ventricular fibrillation

Since the first animal coronary arteriogram in 1933 there have been many innovations in techniques and contrast media. From 1933 through the late 1950s the procedures used involved nonselective aortic injections and the use of acetylcholine to slow the heart. The first selective coronary arteriogram in animals was performed by West, Kobayashi & Guzman in 1958 (45) and in 1959 Guzman & West (7) observed ventricular fibrillation with some media but not others. In 1967 Judkins (14) described the catheter designs for right and left coronary catheterizations that we still use today. In the 1970s and 80s many authors observed the ionic monomeric contrast media reduced plasma calcium causing fibrillation and myocardial depression. Supplementation of ionic media with calcium was shown to moderate these adverse effects. Almen's vision of low osmolality contrast media and the creation of metrizamide (1) stimulated the rapid development of monomeric and dimeric nonionic contrast media. The ionic dimeric medium ioxaglate also provided low osmolality. Digital frame grabbers and computers lead to the development of digital subtraction angiography and new applications of arteriography, frequently using dilute media. Unexpectedly, during prolonged right coronary arteriography in animals, dilute nonionic media were found to produce increased fibrillation as compared to dilute ionic media. The addition of sodium to nonionic media significantly reduced the incidence of fibrillation. Animal studies with the nonionic medium iodixanol supplemented with sodium and calcium (Visipaque) have demonstrated minimal incidences of fibrillation and myocardial depression.

Cardiac effects of iodixanol compared to those of other nonionic and ionic contrast media on the isolated rat heart

This study was designed to compare the cardiac electrophysiology and mechanical effects of iodixanol to those of iotrolan, iopromide, ioxaglate and diatrizoate. Two consecutive injections of contrast media (CM) (0.3 g I/kg and 0.9 g I/kg b.w.) were given to spontaneously beating, Langendorff-perfused rat hearts. CM were given as a single, short-lasting bolus injection (i.e. over 2 and 5 s). Changes in aortic pressure, left ventricular pressures and ECG were continuously recorded during constant volume perfusion. The nonionic CM had less pronounced effects on aortic pressure than had the ionic media. The peak rate of isovolumetric contraction (LV dP/dt(max)) was slightly decreased by iodixanol and iotrolan, slightly more decreased by iopromide and markedly decreased by ioxaglate and diatrizoate. Similarly, the peak rate of pressure decline (LV dP/dt (min)) was only slightly decreased by iodixanol and iotrolan. Also, the 2 nonionic dimers had the smallest effects on the left ventricular end diastolic pressure (LVEDP) and heart rate. Ioxaglate lengthened the PQ-interval, but less so than diatrizoate. THe QT-interval was only slightly lengthened by iodixanol and iotrolan, as compared to the lenghthening caused by iopromide, ioxaglate and diatrizoate. Single ventricular extrasystoles were seen in all groups. Extrasystoles up to 3 coupled beats were registered after ioxaglate and diatrizoate. No episodes of ventricular fibrillation occurred with any CM. In conclusion, the nonionic dimers, and in particular iodixanol, induce only minor changes in cardiac function, whereas the ionic dimer ioxaglate and the ionic monomer diatrizoate induce pronounced effects.

Role of sodium addition to nonionic contrast medium in preventing ventricular fibrillation during coronary arteriography in dogs

RATIONALE AND OBJECTIVES

We studied the effect of the addition of sodium to nonionic contrast medium (CM) on the incidence of ventricular fibrillation (VF) during coronary arteriography in dogs.

METHODS

We infused 20 ml (0.5 ml/sec) of iohexol, iohexol plus 30 mmol of Na+ per liter, and NaCl-Ringer's acetate in randomized order through a wedged catheter placed in the right coronary artery (RCA) or in the left anterior descending coronary artery (LAD) in 12 anesthetized dogs. In addition to electrocardiographic and hemodynamic measurements, epicardial monophasic action potential durations and ventricular activation times were recorded during infusions into the LAD.

RESULTS

All infusions with iohexol into the RCA and the LAD (n = 16) caused VF. Seven of 19 infusions with iohexol plus 30 mmol of Na+ per liter caused VF. Infusions with iohexol plus 30 mmol of Na+ per liter that did not cause VF lengthened monophasic action potential durations and increased ventricular activation times more in the CM-perfused area than in the control area.

CONCLUSION

The addition of sodium to iohexol reduces the incidence of VF when infused through a wedged catheter. The protective mechanisms may be attributable to a lengthened repolarization phase and an increased activation time in the CM-perfused area.

Clinical pharmacology of iomeprol

The pharmacodynamic effects of iomeprol on the cardiovascular, central nervous, coagulation, and complement systems and on renal and thyroid functions using a wide range of intravenous and intraarterial radiological procedures were evaluated in Phase I, Phase II and Phase III clinical studies. The pharmacokinetics and metabolism of iomeprol were studied in healthy volunteers. Iomeprol 350 and 400 mgI/ml at doses ranging from 100 to 300 ml did not cause any significant changes of the basal haemodynamic parameters when used in CT of the chest and upper abdomen. No significant alterations of haemodynamic and ECG parameters were seen in patients who underwent cardiac-angiography or coronary angiography with iomeprol 400 mgI/ml. Intensive monitoring of haemodynamic and EEG parameters in patients undergoing conventional cerebral angiography with iomeprol 300 mgI/ml confirmed good toleration by the CNS. Neither renal and thyroid functions nor the coagulation and complement systems were significantly affected by iomeprol. Iomeprol was not metabolised and did not bind to plasma proteins. In healthy volunteers it was excreted almost exclusively by renal glomerular filtration (about 90% of the injected dose after 24 h). The pharmacokinetic behaviour of iomeprol was very similar to the behaviour of other nonionic, monomeric agents.

Comparison of ionic and non-ionic contrast agents in cardiac catheterization: the effects of ventriculography and coronary arteriography on hemodynamics, electrocardiography, and serum creatinine

We compared two nonionic contrast agents (ioxaglate and iohexol) with an ionic agent (Renografin-76) on the effects of ventriculography and coronary arteriography on the hemodynamics, electrocardiography, and serum creatinine in one hundred consecutive patients. Patients were randomized to nonionic or ionic groups and were further evaluated regarding the effect of fluid loading prior to catheterization. The ionic agent more often produced subjective reactions (rash, nausea/vomiting). Following ventriculography, both ionic and non-ionic agents produced an increase in left ventricular end diastolic pressure and this effect was undetermined by fluid loading. Nonionic agents decreased aortic diastolic pressure following ventriculography and this effect was unaltered by fluid loading. In contrast, the ionic agent produced profound hemodynamic changes (drop in both systolic and diastolic pressures) following coronary arteriography and these effects were blunted by prior fluid loading. The ionic agent produced significantly greater heart rate slowing and prolongation of the QT interval than the nonionic agents, suggesting that the latter are potentially less arrhythmogenic. Comparing the two non-ionic agents, we found that both decreased aortic diastolic pressure and increased left ventricular end diastolic pressure following ventriculography. Iohexol produced greater heart rate slowing than did ioxaglate, though the increase was minor compared to the ionic agent. Neither nonionic agent appeared to significantly affect serum creatinine. In conclusion, the two nonionic agents appeared to offer significant advantages over the ionic agent in ventriculography and coronary arteriography.

Cardiovascular effects of iodinated contrast agents

The ideal intravascular contrast agent would be biologically inert and have no pharmacologic actions. Pharmacologic actions of currently used radiographic contrast agents are determined principally by 3 physicochemical properties of the iodine-bearing molecule and its formulation: osmolality, sodium concentration and calcium-binding properties. Within this framework, the calcium-binding 1.5 ratio agents have the most marked effects, and the 3.0 ratio nonionic agents the least, with the noncalcium-binding formulations of 1.5 ratio agents and ioxaglate (the only 3.0 ratio ionic agent) in between. Differences in hemodynamic effects are predominantly related to osmolality with the 3.0 agents causing less hemodynamic disturbance. The magnitude of difference is small enough that the 3.0 ratio agents have no important clinical advantage when used in patients with good or moderately impaired left ventricular function. However, the difference may be important in patients with severely impaired circulatory performance. The principal electrophysiologic differences are between the calcium-binding 1.5 ratio agents (which are associated with a clear-cut greater frequency of ventricular fibrillation during coronary injection than the noncalcium-binding 1.5 ratio agents) and the 3.0 ratio agents. There is no justification for the use of calcium-binding 1.5 ratio agents, since noncalcium-binding formulations of the same molecule are available at the same price. The circulatory reserve of most patients makes the differences between 3.0 ratio agents and noncalcium-binding 1.5 ratio agents clinically unimportant. In view of the substantial price disparity between 1.5 ratio and 3.0 ratio agents, noncalcium-binding 1.5 ratio agents are appropriate for patients with good circulatory performance and 3.0 ratio agents are best reserved for patients with impaired circulatory performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of meglumine sodium diatrizoate, iopamidol, and iohexol for coronary angiography and ventriculography

Meglumine sodium diatrizoate (Urografin), iopamidol, and iohexol were compared in a double-blind, randomized study of 287 patients undergoing elective cardiac angiography. Ninety-six patients received Urografin, 98 received iopamidol, and 92 received iohexol. The groups were similar in all respects. Variables measured before and after contrast injection were left ventricular end-diastolic pressure (LVEDP), left ventricular systolic pressure (LVSP), systolic arterial pressure (SAP), RR, PR, and QTc intervals, QRS duration, ST segment change greater than 2 mm, arrhythmias, and symptoms. The adequacy of coronary and ventricular opacification was assessed by two experienced observers. Following left ventriculography, small rises in LVEDP occurred with iopamidol and iohexol (mean +/- SD: 18 +/- 7 to 21 +/- 7 mmHg) and a moderate fall in LVSP with Urografin (150 +/- 32 to 133 +/- 32 mmHg). Following coronary angiography there was a progressive fall in SAP (130 +/- 26 to 117 +/- 30 mmHg) and prolongation of RR intervals (900 +/- 138 to 1,266 +/- 692 msec) and QTc (440 +/- 61 to 471 +/- 73 msec) and QRS duration (87 +/- 25 to 100 +/- 27 msec) with Urografin. There was a small fall in SAP with iopamidol (138 +/- 25 to 128 +/- 27 mmHg) and prolongation of QRS duration with iohexol (85 +/- 29 to 90 +/- 24 msec). Other parameters were not significantly affected. Frequent bradyarrhythmias (sinus pause 14.5%, asystole 6%) and ST segment depression occurred following Urografin. Urografin was less well tolerated, with 10% of patients experiencing severe nausea or vomiting and 30% of patients experiencing extreme heat sensation. Differences between iohexol and iopamidol were minor.(ABSTRACT TRUNCATED AT 250 WORDS)

Thromboembolic complications in coronary angiography associated with the use of nonionic contrast medium

Thromboembolic complications occurred during diagnostic coronary arteriography in three patients in spite of systemic heparinization. These mishaps were associated with the use of a nonionic contrast medium, which is known not to have a significant protective effect on coagulation pathways. If nonionic contrast media are to be used in angiographic studies of critical organs, meticulous technique is imperative, and adequate systemic heparinization is recommended.

Effect of calcium-binding additives on ventricular fibrillation and repolarization changes during coronary angiography

Ventricular fibrillation during coronary angiography with Renografin-76 (meglumine sodium diatrizoate) has been attributed to the calcium-binding additives sodium citrate and sodium ethylenediaminetetraacetic acid (EDTA), which may produce repolarization changes manifested as prolongation of the QT interval. Angiovist-370 is a newer form of meglumine sodium diatrizoate that contains calcium EDTA as its additive and thus has a decreased calcium-binding effect. Eight hundred sixteen patients were prospectively randomized to receive either Renografin-76 or Angiovist-370. Ventricular fibrillation occurred in 10 of 410 patients receiving Renografin-76 and in 0 of 406 patients given Angiovist-370 (p less than 0.0005). Clinical data were analyzed without knowledge of other data in the 10 patients treated with Renografin-76 who had ventricular fibrillation (Group I), 103 randomly selected patients who also received Renografin-76 but had no ventricular fibrillation (Group II) and 108 randomly selected patients given Angiovist-370 (Group III). Of several variables examined, only the QT interval differentiated patients receiving Renografin-76 and Angiovist-370. The mean corrected QT interval (QTc interval) before coronary angiography was slightly but not significantly (p = 0.7) higher in Group I than in Groups II and III. Ten seconds after the first left coronary artery injection it was more prolonged in Groups I and II (0.552 and 0.561 second, respectively) than in Group III (0.448 second) (p less than 0.00005). Similarly, 10 seconds after the first right coronary artery injection it was significantly longer in Groups I and II (0.545 and 0.544 second) than in Group III (0.477 second) (p less than 0.00005).(ABSTRACT TRUNCATED AT 250 WORDS)

Aortocervical angiography with high and low osmolality ionic contrast media. A clinical investigation of metrizoate and ioxaglate

The influence of aortic arch injection of metrizoate 280 and 370 mg I/ml and ioxaglate 280 and 320 mg I/ml on EEG, heart rate, blood pressure, subjective responses, occurrence of involuntary movements and resulting image quality was investigated in 31 patients. Ioxaglate 320 produced less haemodynamic changes and subjective responses and as good image quality as the hyperosmolar contrast medium metrizoate 370 if subtraction procedure was used. Small and brief EEG changes were recorded in 9 of 14 patients. Only metrizoate 280 induced significant bradycardia. Involuntary movements on the film with the best demonstration of the vessels occurred with no difference between the contrast media. There was no correlation between involuntary movements and image quality. Our investigation indicates that an ionic contrast medium which is intended for aortocervical angiography should have a concentration of at least 320 mg I/ml, high viscosity, low osmolality and be no pure meglumine salt.

Ventricular fibrillation during coronary angiography: an analysis of mechanisms

To investigate the mechanisms of ventricular fibrillation (VF) during coronary angiography, we assessed ventricular automaticity, local QT intervals, local conduction characteristics, and the ability to induce arrhythmias with premature ventricular stimulation in 30 dogs after intracoronary injections of 4 to 6 cc of Renografin 76 (RG 76). Ventricular automaticity was measured in six dogs as the idioventricular escape rate following intense vagal stimulation and was unchanged (51 +/- 6 vs 52 +/- 6 bpm, p greater than 0.05) with 6 cc of RG 76. In addition, 8 of 10 injections of 6 cc of RG 76 produced VF at a heart rate of 200 bpm compared to only 2 of 10 injections at a heart rate of 80 bpm (p less than 0.05). Composite and bipolar plunge electrodes were placed in the region perfused by the left anterior descending coronary artery (LAD) and circumflex coronary artery to assess QT intervals and conduction characteristics. RG 76, 4cc, produced a 116 +/- 18 msec increase in the QT intervals recorded from the region perfused by the LAD, resulting in a marked dispersion in repolarization. Both local bipolar and composite electrograms showed minimal conduction delay, which rarely extended beyond the QRS of a lead II ECG during atrial paced rhythm. As premature beats (spontaneous or induced) conducted through the region of QT prolongation, marked conduction delay was recorded from bipolar electrograms, while composite electrograms recorded continuous fractionated electrical activity spanning the diastolic interval at the onset of VF.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventricular arrhythmias during coronary angiography in patients with angina pectoris or chest pain syndromes

Of 7,915 patients undergoing coronary angiography from 1978 to 1983, 39 (25 men and 14 women with a mean age of 57 years [range 37 to 79]) had sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) during the procedure. Nine patients had atypical chest pain and 30 had typical angina. Fifteen had had a previous myocardial infarction. One patient had a history of VT or VF. Electrocardiograms taken at rest revealed a prolonged QT interval in 14. A normal ejection fraction was found in 79%. Coronary angiography revealed that 10 patients had 3-vessel disease, 15 had 1- or 2-vessel disease and 14 had normal coronary arteries. The VT or VF was seen with injection of contrast medium into the right coronary artery in 24, the left coronary artery in 10 and vein bypass grafts in 5 patients. Of the episodes of VT or VF, 67% occurred after injection of contrast medium into a minimally diseased coronary artery. In patients in whom VT or VF occurred after injection into a minimally diseased coronary artery, the arrhythmia was preceded by bradycardia, usually with pronounced widening of the QRS and QT intervals. This response was significantly different from that in patients in whom VT or VF occurred after injection into a coronary artery with significant stenosis; in these patients, VT or VF was initiated by a single premature ventricular contraction on a T wave. VT or VF was successfully cardioverted in all instances, without further arrhythmias.

Changes in QTc interval induced with Renografin-76 and Hypaque-76 during coronary arteriography

Renografin-76 and Hypaque-76 are both recommended for coronary arteriography. Both have the same osmolality and iodine concentration, but differ in their calcium binding properties. After selective right or left coronary arteriography in patients, Renografin-76 caused significantly more prolongation of the QTc interval than did Hypaque-76. Less calcium binding in the Hypaque formulation is probably responsible for its lesser effect on the QTc interval. This study suggests, but does not prove, that Hypaque-76 is safer than Renografin-76 for coronary arteriography.

Inotropic action of tolbutamide on human myocardium

The inotropic action of tolbutamide previously demonstrated in vitro was evaluated in 15 nondiabetic subjects during diagnostic cardiac catheterization. Following bolus injection of 250 mg of tolbutamide intravenously, a rise of serum insulin and a slight fall of serum potassium were observed. Inotropic response was determined from significant fall in PEP/LVET ratio, significant fall of left ventricular end-diastolic pressure, shift to an augmented function curve in work-pressure relationships, and prominent rise of dP/dt values at comparable heart rates. The inotropic effect was greatest at 5-15 min with return to near control values at 30 min. An unusually marked inotropic response was observed in one subject. While the measurable net hemodynamic effect of tolbutamide in the human heart is small, its effect on ischemic and normal areas within the heart of a diabetic patient with atherosclerosis may be different. Thus, its ultimate effect on the diseased heart may be significant.