Correlation of the location of coronary arterial spasm with the lead distribution of ST segment elevation during variant angina

Coronary spasm and acute myocardial infarction due to a mutation (V734I) in the nucleotide binding domain 1 of ABCC9

BACKGROUND

Alterations in coronary vasomotor tone may participate in the pathogenesis of acute myocardial infarction (AMI). Vascular ATP-sensitive K(+) (KATP) channels, formed by Kir6.x/SUR2B, are key regulators of coronary tone and mutations in cardiac (Kir6.2/SUR2A) KATP channels result in heart disease. Here we explore the pathophysiological mechanism of a rare mutation (V734I) found in exon 17 of the ABCC9 gene, estimated to cause a 6.4-fold higher risk of AMI before the age of 60.

METHODS AND RESULTS

Eleven patients carrying the mutation were identified; they presented AMI of vasospastic origin associated with increased plasma levels of endothelin-1 and increased leukocyte ROCK activity. The effects of the mutation on the functional properties of the two splice variants of ABCC9 (SUR2A and SUR2B) were studied using patch-clamp electrophysiology. The mutation reduced the sensitivity to MgATP inhibition of Kir6.2/SUR2B channels but not of Kir6.2/SUR2A and Kir6.1/SUR2B channels. Furthermore, the stimulatory effects of MgNDP (MgADP, MgGDP and MgUDP) were unaltered in mutant Kir6.2/SUR2A and Kir6.1/SUR2B channels. In contrast, mutant channels composed of Kir6.2 and SUR2B were less sensitive to MgNDP activation, assessed in the presence of MgATP. The antianginal drug nicorandil activated Kir6.2/SUR2B-V734I channels, thus substituting for the loss of MgNDP stimulation, suggesting that this drug could be of therapeutic use in the treatment of AMI associated with V734I.

CONCLUSIONS

The 734I allele in ABCC9 may influence susceptibility to AMI by impairing the response of vascular, but not cardiac, KATP channels to intracellular nucleotides. This is the first human mutation in an ion channel gene to be implicated in AMI.

Recent insights into the mechanisms of vasospastic angina

Coronary artery spasm plays an important role in the pathogenesis of many types of ischemic heart disease, not only in vasospastic angina but also in myocardial infarction and sudden death, particularly in the asian population. Patients with vasospastic angina are known to have defective endothelial function due to reduced nitric oxide bioavailability. Moreover, markers of oxidative stress and plasma levels of C-reactive protein are elevated. Smoking, polymorphysms of endothelial nitric oxide synthetase (eNOS), and low-grade inflammation have been regarded as the most important risk factors for vasospastic angina. The recent body of evidence indicates that RhoA and its down stream effector, ROCK/Rho-kinase, are associated with hypercontraction of vascular smooth muscle of the coronary artery and regulation of eNOS activity. Thus, endothelial dysfunction through abnormalities of eNOS and enhanced contractility of vascular smooth muscle in coronary artery segments are considered major mechanisms in vasospastic angina. However, the precise mechanisms for coronary vasospasm are not well understood. This article will review current understanding of the mechanism of coronary artery spasm.

Neurovascular pharmacology of migraine

Migraine is a paroxysmal neurovascular disorder, which affects a significant proportion of the population. Since dilation of cranial blood vessels is likely to be responsible for the headache experienced in migraine, many experimental models for the study of migraine have focussed on this feature. The current review discusses a model that is based on the constriction of carotid arteriovenous anastomoses in anaesthetized pigs, which has during the last decades proven of great value in identifying potential antimigraine drugs acting via a vascular mechanism. Further, the use of human isolated blood vessels in migraine research is discussed. Thirdly, we describe an integrated neurovascular model, where dural vasodilatation in response to trigeminal perivascular nerve stimulation can be studied. Such a model not only allows an in-depth characterization of directly vascularly acting drugs, but also of drugs that are supposed to act via inhibition of vasodilator responses to endogenous neuropeptides, or of drugs that inhibit the release of these neuropeptides. We discuss the use of this model in a study on the influence of female sex hormones on migraine. Finally, the implementation of this model in mice is considered. Such a murine model allows the use of genetically modified animals, which will lead to a better understanding of the ion channel mutations that are found in migraine patients.

New Holter Monitoring Analysis System-Synthesizing 12-Lead Electrocardiograms Using a Calculation of the Lead Vectors-

BACKGROUND

A new system of synthesizing a 12-lead electrocardiogram (Syn-ECG) with practically identical waveforms to the standard 12-lead ECG (Stn-ECG) from 3-channel ECGs recorded by Holter monitoring has been developed.

METHODS AND RESULTS

The study group comprised 16 healthy individuals and 13 patients with abnormal ECGs. The bipolar eV1, eV5 and eVF leads were recorded using digital Holter monitoring and nine Syn-ECGs, corresponding to each lead of the Stn-ECG, were synthesized. The 9 ECGs consisted of a theoretical Syn-ECG and 8 Syn-ECGs positioned around the theoretical Syn-ECG at 3 cm intervals on the Frank's image surface. Of the 9 ECGs, the Syn-ECG with the maximum product of the cross-correlation coefficient of the QRS wave and that of the T wave, was automatically selected as the optimal Syn-ECG. The amplitude data from the QRS wave, R wave, T wave, and ST level, and also the amplitude ratio of the R wave, T wave to the QRS wave, were significantly well correlated between the Syn-ECG and Stn-ECG.

CONCLUSIONS

A practically identical ECG morphology, comparable with a Stn-ECG, was successfully created using this system.

Tl-201 scintigraphy in multivessel exercise-induced variant angina

A 53-year-old man presented for evaluation of nocturnal chest pain, consistent with angina pectoris. An exercise stress test reproduced his symptoms, however, exercise electrocardiograms were nondiagnostic. An exercise-thallium perfusion study confirmed vasospasm as the cause. This knowledge guided subsequent successful medical therapy.

Clinical observation of spontaneous anginal attacks and multivessel spasm in variant angina pectoris with normal coronary arteries: evaluation by 24-hour 12-lead electrocardiography with computer analysis

OBJECTIVES

Using a new, computerized 24-h 12-lead electrocardiographic (ECG) recording and analysis system (the EAGLE system), we sought to evaluate the clinical manifestations of ischemic episodes in patients with variant angina and normal coronary arteries.

BACKGROUND

Although the prognosis of variant angina without significant organic stenosis is generally good, the incidence of multivessel spasm, a major prognostic factor, is surprisingly high in provocation tests.

METHODS

A total of 122 patients with suspected variant or unstable angina underwent 24-h examination with the EAGLE system and two-channel Holter monitoring. Thirty patients in this group were diagnosed as having variant angina with normal or nearly normal coronary arteries. Twenty-two (73%) of these 30 patients developed anginal attacks with ST segment elevation during monitoring and were enrolled in the study.

RESULTS

The 22 patients had a total of 138 episodes of transient ST segment elevation and 13 episodes of ST segment depression. No arrhythmias were observed during ST segment depression, but 26 episodes of ST segment elevation (19%) were associated with arrhythmias: 7 with premature ventricular contractions, 3 with ventricular bigeminy, 3 with complete atrioventricular (AV) block, 1 with complete AV block and couplets of premature ventricular contractions and 12 with marked sinus bradycardia (< 45 beats/min). Ten (45%) of the 22 patients had multivessel spasm. We observed three different patterns of multivessel spasm: 1) spasm at a different site on different occasions (migratory spasm); 2) spasm that sequentially affected two different sites; 3) simultaneous spasm at more than one site. The duration of ST segment elevation was much longer in patients with sequential and simultaneous spasm than in those with single-vessel spasm, and arrhythmias were more frequent during these two types of multivessel spasm.

CONCLUSIONS

Although the prognosis of multivessel spasm is believed to be poor, this may not necessarily be so. Anginal attacks due to sequential and simultaneous multivessel spasm seem to be more dangerous than those involving single-vessel spasm or migratory multivessel spasm.

Efficacy of three-channel ambulatory electrocardiographic monitoring for the detection of myocardial ischemia

The recognition of silent myocardial ischemia (SMI) has been demonstrated to have important clinical relevance. Two-channel ambulatory (Holter) electrocardiographic recording is a commonly utilized method for detecting transient electrocardiographic ST segment changes representative of SMI. It has been suggested that the analysis of two channels alone may not adequately detect SMI. We therefore evaluated the diagnostic yield of three channels using a three-channel electrocardiographic monitoring device in 46 consecutive patients (age 61 +/- 9 years) undergoing percutaneous transluminal coronary angioplasty of an isolated single-vessel stenosis. Modified bipolar chest leads V2, V5, and AVF (CM-V2, CM-V5, and CS-AVF) were utilized for analysis. The percent detection of ST segment changes from various combinations of two-lead recordings were compared to the total three leads, and an absolute transient ST segment shift (STSS) of greater than or equal to 1 mm during balloon inflation was considered as evidence of myocardial ischemia. One patient was excluded because of the need for ventricular pacing during balloon inflation. A total of 33 of 45 patients had STSS in all three leads (percent detection = 73%), while 32 (71%) had STSS in the two-lead grouping with the highest diagnostic yield (CM-V2/CM-V5; p = ns). Of the various two-lead combinations studied, leads CM-V2 and CM-V5 provided the best lead set overall for the detection of ischemic STSS. Three-channel ambulatory electrocardiographic recording only marginally improves upon the detection of ischemia when compared with standard (CM-V2/CM-V5 or CM-V5/CS-AVF) two-channel ambulatory electrocardiographic recordings.

Evaluation of a newly devised three-lead Holter recording during treadmill testing in the diagnosis of ischemic ST changes

Sixty-five patients (54 men, 11 women) with angina pectoris were studied using a technique for recording a 3-lead electrocardiogram without increasing the number of channels and electrodes in the commercial 2-channel Holter recorder. In 52 of the 65 patients, simultaneous ECGs with both the 3-lead Holter method and the conventional 12-lead system during treadmill exercise testing were performed. The results of the two systems in detecting significant ST depressions were consistent in 51 of 52 patients (98%). Twenty-seven of the 32 patients with significant coronary stenosis showed ST depressions during exercise both in the 3-lead Holter and the 12-lead ECG systems. There were cases in which ST depressions were confined only to the CM2 lead (n = 1), the CM5 lead (n = 18) or the CMf lead (n = 3). This indicates that at least three leads are needed in the Holter system for the detection of certain ST changes. The sensitivity of the Holter system during exercise in detecting significant coronary artery disease was the same as that of the 12-lead system (84%). Two of the total 65 patients had variant angina at night. No ST changes in the CM5 lead were observed in either case. Thus, the 3-lead Holter monitoring technique is as accurate as the 12-lead system for the detection of ischemic ST depressions associated with coronary stenosis and is unlikely no miss the signs of variant angina. In addition, this technique is expandable since it can continuously switch between leads using the same channel.

Effects of intracoronary injection of ergonovine on angiographic normal coronary arteries: study of 108 consecutive patients

To assess the local and systemic intracoronary (IC) ergonovine maleate (EM), single or repeated 25 micrograms bolus injections were administered to 108 consecutive patients with chest pain and normal coronary arteriograms. Coronary artery spasm (CAS) was induced in 17 (15.7%) patients. None of these patients developed ST-segment depression, and ST-segment elevation appeared in only 6 (35.3%). In 59 of the 91 patients without CAS, both the IC and the intravenous (IV) EM arteriographic and hemodynamic effects were compared. The mean diameter of the vessels was reduced by 15% (p less than 0.001) after two single 25 micrograms ICEM injections. Only insignificant changes were induced in the heart rate (baseline 80 +/- 15; after ICEM 79 +/- 15 beats/min; p = NS) and systolic aortic pressure (baseline 147 +/- 27; after ICEM 149 +/- 28 mmHG; p = NS). Following 350 micrograms of cumulative IVEM, the mean coronary diameter decreased by 20% (p less than 0.01 vs. ICEM dose) and the heart rate diminished slightly (76 +/- 12 beats/min, p less than 0.01). However, the systolic aortic pressures did increase by 16% (171 +/- 28 mmHg; p less than 0.001). No major complications were observed. Thus, to induce CAS the IC delivery route appears to be safe, allows for more accurate titration, and adverse systemic effects, such as hypertension, are avoided.

Significance of coronary artery tone in patients with vasospastic angina

To investigate the relation between basal coronary artery diameter and development of coronary artery spasm, the diameters of the proximal, middle and distal segments of the three major coronary artery branches, together with that of the left main trunk, were measured on a control angiogram and after ergonovine and nitrate administration in 30 patients with vasospastic angina without significant organic stenosis, and in 35 patients without ischemic heart disease. The percent change in coronary diameter after ergonovine and nitrate administration compared with the control diameter was used as an index of coronary vasoreactivity. In patients with vasospastic angina, coronary artery responses to both ergonovine and nitrate were greater in the spastic segments than in the other segments (p less than 0.05), and those of the coronary arteries without spasm were greater than those of the coronary arteries in patients without ischemic heart disease (p less than 0.01). There were no significant differences between the coronary artery diameters in the two groups after nitrate administration, and the control diameters were less in patients with vasospastic angina than in patients without ischemic heart disease. These observations indicate that a coronary vasomotion disorder, which involves increased basal coronary artery tone and hypersensitivity to vasoconstrictive stimuli, not only at a localized segment but also in the entire coronary artery tree, is present in patients with vasospastic angina. Clinically, evaluation of basal coronary artery tone may be useful for predicting the occurrence and location of coronary artery spasm.

Hyperventilation-induced simultaneous multivessel coronary spasm in patients with variant angina: an echocardiographic and arteriographic study

Left ventricular wall motion abnormalities during an attack of coronary spasm induced by hyperventilation were examined with use of two-dimensional echocardiography in 27 patients with variant angina. Transient abnormal wall motion (asynergy) confined to one coronary artery region was found in 18 of the 27 patients and transient abnormal motion extending over more than one coronary artery region in the remaining 9 patients. Spasm of more than one major coronary artery was demonstrated separately by coronary arteriography during an attack induced by injection of acetylcholine or ergonovine in seven of the nine patients who manifested asynergy in more than one coronary artery region. In one patient, spasm was demonstrated in one major coronary artery, and the other coronary arteries were severely stenosed or occluded organically. In the remaining patient, acetylcholine was not injected into both arteries; however, the attack was sometimes associated with ST segment elevation in the anterior leads and at other times in the inferior leads. Therefore, simultaneous multivessel coronary spasm seems to have occurred in eight of the nine patients who exhibited asynergy in more than one coronary artery region. The 8 patients with simultaneous multivessel coronary spasm had a higher degree and longer duration of ST segment elevation and a higher incidence of arrhythmias during the attack induced by hyperventilation than did the 19 patients with single vessel coronary spasm, and all of them had no significant organic stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Inverted U wave in ergonovine-induced vasospastic angina

The relationship between inverted U wave in leads V5 and II and the location of myocardial ischemia was studied in 52 positive patients and in 50 negative patients with ergonovine provocation test. Development of a biphasic or negative U wave, or increased negativity of U wave (inverted U wave) was observed in 15 of 17 patients with spasm in only the right coronary artery (RCA), in 6 of 8 with spasm in only the left anterior descending artery (LAD), in 2 of 8 with spasm in only the left circumflex artery (LCx), and in 23 of 24 with spasm in two or more vessels. Of 52 positive patients in the ergonovine provocation test, 46 (88.5%) had inverted U wave. Of these, 17 (32.7%) had inverted U wave without discernible ST deviation. Of 50 negative patients, 2 had inverted U wave. Inverted U wave in lead V5 was frequently seen in patients with spasm of LAD, but this finding was not uncommon in spasm of RCA or LCx. On the other hand, inverted U wave in lead II was frequently seen in spasm of RCA and LCx, but not in spasm of LAD. These findings suggest that inverted U wave in lead V5 is not specific for myocardial ischemia due to spasm of LAD and that inverted U wave in lead II is specific for spasm of RCA and LCx.

Simultaneous multivessel coronary artery spasm demonstrated by quantitative analysis of thallium-201 single photon emission computed tomography

Thallium-201 myocardial scintigraphy with quantitative analysis of emission computed tomography was performed during episodes of angina in 19 patients with variant angina and nearly normal coronary arteriographic findings. Eleven patients (group I) were shown by arteriography to have spasm in 2 or more large coronary arteries. Eight patients (group II) had spasm in only 1 coronary artery. In 7 patients in group I, significant diffuse perfusion defects simultaneously appeared in multiple coronary artery regions on the scintigram (group IA). The extent and severity of the perfusion defect as measured by thallium-201 tomography were significantly greater in group IA than in group II (p less than 0.001 and p less than 0.01, respectively). The duration of transient ST-segment elevation during the attack in group IA was significantly longer than in group II (p less than 0.001). The incidence of ventricular arrhythmias, including ventricular tachycardia, or complete atrioventricular block during the anginal attack was significantly higher (p less than 0.05) in group IA than in group II. In all study patients, neither attack nor scintigraphic perfusion defect appeared on the repeat test after oral administration of nifedipine. In conclusion, multivessel coronary artery spasm simultaneously appears and causes the attack in many patients with variant angina and nearly normal coronary arteriographic findings, and myocardial ischemia due to simultaneous multivessel coronary spasm is likely to be more extensive and severe, persist longer and have a higher frequency of potentially dangerous arrhythmias than that due to spasm of only 1 coronary artery.

Clinical assessment of elastic properties of large coronary arteries: pressure-diameter relationship and dynamic incremental elastic modulus

Vascular elastic properties in vivo (dynamic incremental elastic modulus [Ep(dyn)]) of large coronary arteries were assessed from the pressure-diameter relationships of the large coronary arteries in 46 patients with suspected ischemic heart disease. Ep(dyn) represents the vascular stiffness primarily determined by the organic sclerotic changes of the vascular wall and the vascular smooth muscle tone. Coronary arterial diameter was obtained from the magnified cine coronary arteriograms by using a computerized caliber measurement technique. The mean Ep(dyn) of the left main coronary artery and the proximal portions of the left anterior descending and circumflex coronary arteries with apparently normal angiograms were significantly (P less than 0.01) increased as the number of involved coronary vessels was increased. Mean Ep(dyn) values in multi-vessel disease were comparable with those of dilated segment by the percutaneous transluminal coronary angioplasty, indicating that the vascular sclerotic changes are not localized to the narrowed segments but diffusely distributed to the angiographically normal vascular wall. In 4 patients who had successful percutaneous transluminal coronary angioplasty, Ep(dyn) of the dilated coronary segment showed markedly higher values (0.21-0.30 X 10(6) Nm-2) than the normal values (0.16 +/- 0.06 X 10(6) Nm-2 in left anterior descending coronary artery). In contrast, there was no significant difference in Ep(dyn) values of the angiographically normal left main coronary trunk, proximal portions of left anterior descending and circumflex arteries between patients with and without vasospastic angina. During myocardial ischemia induced by ergonovine maleate, vasospastic response of the non-diseased segment was comparable with that in patients who did not have an anginal attack during the ergonovine test. Thus, in contrast to the sclerotic change, abnormal vasoconstrictive property of the coronary artery may be localized to the diseased segment.

Clinical and research applications of ambulatory Holter ST-segment and heart rate monitoring

Monitoring of the electrocardiogram during normal daily activity yields data regarding silent myocardial ischemia and its relation to heart rate in addition to the detection of cardiac arrhythmias. In recent years various techniques have been developed to quantify the frequency and duration of ischemic episodes in patients with ischemic heart disease. Of particular importance are the newer frequency-modulated recording techniques, which ensure adequate low frequency response, and the computerized digital analysis used to define the role of ST-segment monitoring in the clinical and research setting. The techniques used for acquiring artifact-free signals, the methods of data analysis and the clinical role of ambulatory Holter monitoring of ST-segment changes in the diagnosis of Prinzmetal's angina, in chronic stable angina and in the detection of calcium antagonist withdrawal syndrome in angina are discussed. The data indicate the particular utility of Holter monitoring to analyze the variability of heart rate in defining the effects of calcium-channel blockers, beta-adrenergic blocking agents and their combined use in pharmacologic therapy of ischemic myocardial syndromes.

Prinzmetal's variant angina evolved in inferior myocardial infarction with involvement of the right ventricle: sequential radionuclide evaluation

A patient with Prinzmetal's variant angina (PVA) who developed an inferolateral myocardial infarction with right-ventricle involvement was studied using sequential radionuclide imaging until 5 months after the acute event. The patient also underwent-contrast ventriculography and coronary-artery angiography. Equilibrium-gated radionuclide angiography (EGRA) revealed the localization of ventricular dysfunction, the results obtained being in agreement with haemodynamic data. We emphasize the usefulness of the parameters obtained using EGRA (regional wall motion, systolic and diastolic parameters) in planning therapy and follow-up.

Transient changes in left ventricular mechanics during attacks of Prinzmetal's angina: an M-mode echocardiographic study

M-mode echocardiograms were recorded in 12 patients with Prinzmetal's angina during 29 episodes of transient myocardial ischemia at rest (18 spontaneous and 11 ergonovine-induced). At peak ST segment elevation a regional mechanical impairment was observed in the interventricular septum during 23 episodes of angina and in the posterior wall during six episodes. In the 18 spontaneous episodes the left ventricular ischemic wall, when compared to the basal state, was found to have a significant reduction in motion (-76.3 +/- 9.1%) (mean +/- SEM), in diastolic thickness (-11.7 +/- 2.5%), and in percent systolic thickening (-88.0 +/- 5.6%). Increase in left ventricular end-diastolic diameter (+13.1 +/- 2.1%) and decrease in percent fractional shortening (-38.1 +/- 3.7%) were also observed. When ST segment was back to the isoelectric line, a transient overshoot in regional left ventricular function was observed. In induced episodes statistically significant changes could be detected by M-mode echocardiography even before appearance of ST segment elevation and anginal pain. No significant difference was found in type or degree of mechanical impairment between induced and spontaneous episodes. Therefore, in patients with Prinzmetal's angina: (1) M-mode echocardiography allows detection of mechanical changes due to transient myocardial ischemia; and (2) mechanical impairment occurs earlier than clinical (pain) and electrocardiographic (ST segment elevation) signs of transmural ischemia.

U wave inversion during attacks of variant angina

Sequential 12 lead electrocardiograms were recorded during angina pectoris induced by ergonovine maleate in 38 patients with variant angina. Transient U wave inversion was observed in 17 patients with ST segment elevation in anterior chest leads, but in only three of 21 patients with ST segment elevation in the inferior leads associated with right coronary artery spasm. In the 17, all of whom had spasm of the left anterior descending coronary artery, the sensitivity of ST segment elevation in V5 was only 41%, and that of U wave inversion 71%. U wave inversion without ST segment elevation occurred during attacks in 35% of patients. During the recovery phase, the sensitivity of U wave inversion was 82% in V4 and 65% in V5, though ST segment elevation was absent in both V4 and V5. Thus, inverted U waves without ST segment elevation often appear in marginal ischaemic zones or during the time of recovery from temporary ischaemia. Detection of inverted U waves should aid in the diagnosis of variant angina when only lead V5 is used as a monitor and when electrocardiograms are recorded only during the recovery phase.

Simultaneous recording of continuous arterial pressure, heart rate, and ST segment in ambulant patients with stable angina pectoris

Simultaneous and accurate recording of arterial blood pressure and ST segment changes is fraught with technical difficulties. We have developed a new system to enable accurate reproduction of the electrocardiogram and intra-arterial blood pressure, using a transducer/perfusion unit conventionally used to study hypertensive subjects, linked to a frequency modulated tape recorder. Detailed methods of digital analysis have been developed to process the data. This system has been used to study 22 patients with arteriographically proven severe obstructive coronary artery disease who suffered frequent attacks of angina. Control data from quantified dynamic exercise in the laboratory were used for comparison with the effects of normal daily activities outside the hospital and to test the hypothesis that "double product" (heart rate X systolic blood pressure) is relevant to the onset of angina in such patients. The most important finding was that both angina and asymptomatic episodes of ST segment depression were invariably accompanied by an increase in heart rate, whereas there was considerable variation in blood pressure changes ranging from an increase to a substantial fall. This suggests that heart rate changes are more important in determining ischaemic episodes than blood pressure. Furthermore, the "double product" was not reproducible during repeated episodes of angina and asymptomatic ischaemia and did not appear to have an important role in the pathogenesis of intermittent myocardial ischaemia in this group of patients.

Calcium antagonists. Clinical use in the treatment of angina

Angina pectoris results from an imbalance between the oxygen supply and the oxygen needs of the myocardium. While the classic form of angina is usually caused by demands exceeding supply, a primary and transient decrease in coronary blood flow is more and more often recognised as an aetiological factor of myocardial ischaemia. Calcium antagonists, although new in cardiovascular therapeutics, are already recognised as the treatment of choice for some forms of angina and as useful therapeutic adjuncts in others. Few contraindications to their use exist. They are potent vasodilators and they can prevent the occurrence of coronary artery spasm responsible for the Prinzmetal's variant form of angina. They can also reduce coronary artery tone, which if high, can compromise flow through a narrowed coronary artery. Nifedipine, diltiazem and verapamil can also influence the various determinants of myocardial oxygen consumption to reduce myocardial oxygen needs. Their effects on heart rate, blood pressure and on the inotropic state of the left ventricle is, in vivo, the balance between their direct effects on the vascular wall and myocardial muscular cells and their indirect effects represented by the reflex physiological responses. Significant variations in these effects exist between the 3 calcium antagonists such that treatment can be individualised to a particular patient's needs. Precautions with their use as well as most of their side effects can be understood from a knowledge of their direct and indirect properties. Other pharmacological effects of these drugs include a regional redistribution of coronary blood flow, cardioprotection, delay in cell death and possibly in the progression of atherosclerosis. The clinical significance of these properties remains to be investigated.