Intravenous nitroglycerin for the treatment of angina at rest unresponsive to standard nitrate therapy

Nitroglycerin Use in the Emergency Department: Current Perspectives

Nitroglycerin, a fast-acting vasodilator, is commonly used as a first-line agent for angina in the emergency department and to manage chest pain due to acute coronary syndromes. It is also a treatment option for other disease states such as acute heart failure, pulmonary edema, and aortic dissection. Nitroglycerin is converted to nitric oxide, a potent vasodilator, in the body, leading to venodilation at lower dosages and arteriodilation at higher dosages that results in both preload and afterload reduction, respectively. Although nitroglycerin has historically been administered as a sublingual tablet and/or spray, it is often given intravenously in the emergency department as this enables titration to effect with predictable pharmacokinetics. In this review article, we outline the indications, mechanism of action, contraindications, and adverse effects of nitroglycerin as well as review relevant literature and make general recommendations regarding the use of nitroglycerin in the emergency department.

Non-ST-Segment Acute Coronary Syndromes

Acute coronary syndrome (ACS) represents an umbrella of ischemic myocardial disease and diagnoses encompassing unstable angina (UA), non-ST-elevation myocardial infarction (NSTEMI), and ST-elevation myocardial infarction (STEMI). UA and NSTEMI for all intents and purposes, share similar pathophysiology, but at increasing severity. This article focuses on the diagnosis, risk stratification, management, and strategies that impact outcomes in NSTEMI.

2018 Guidelines of the Taiwan Society of Cardiology, Taiwan Society of Emergency Medicine and Taiwan Society of Cardiovascular Interventions for the management of non ST-segment elevation acute coronary syndrome

In Taiwan, the incidence of non-ST segment elevation acute coronary syndrome (NSTE-ACS) continues to increase in recent years. The purpose of this guideline is to help health care professionals in Taiwan to use adequate tests and treatments for management of NSTE-ACS. For rapid diagnosis, in addition to history and physical examination, 0/3 h rapid diagnosis protocol with high sensitivity cardiac troponin assay is recommended in this guideline. Dual antiplatelet and anticoagulation therapies are important parts in the initial treatment. Risk stratification should be performed to identify high risk patients for early coronary angiography. Through evaluation of the coronary anatomy and other clinical factors, the decision for coronary revascularization, either by percutaneous coronary intervention or coronary artery bypass grafting, should be decided by the heart team. The duration of dual antiplatelet therapy should be given for at least 12 months after discharge. Other secondary preventive medications are also recommended for long term use.

Unstable Angina Pectoris: An Interventional Approach to Management

The therapy of unstable angina has changed consider ably in the last 15 years. An improved understanding of the pathophysiology has led to many of the changes. Thrombus, platelet activation, progression of athero sclerosis, and coronary vasospasm all appear to have a role. Initial management in unstable angina should begin with aggressive medical therapy with nitrates, calcium antagonists, beta blockers, and aspirin. In patients who are refractory to aggressive medical management, early cardiac catheterization and coronary arteriography is in dicated. The literature appears to confirm that patients with unstable angina who are stabilized with aggressive medical therapy fare as well as those treated with emer gency bypass surgery. Percutaneous transluminal coro nary angioplasty (PTCA) is the treatment of choice in medically refractory unstable angina patients with single-vessel coronary disease.

New approaches include culprit lesion angioplasty, thrombolytic therapy, coronary sinus retroperfusion, and new catheter-based revascularization methods such as intracoronary stents, laser methods and atherectomy. Culprit lesion angioplasty involves angioplasty of only the angina-producing artery in patients with multivessel coronary disease. Early data suggest that this may be an effective short-term alternative to multivessel PTCA or bypass surgery. Recent data also suggest a beneficial role for thrombolytic therapy and synchronized coronary si nus retroperfusion with arterial blood in patients with unstable angina. New catheter-based approaches are in the early stages of development, and their eventual role in the treatment of coronary artery disease and unstable angina remains to be elucidated.

Side effects of using nitrates to treat heart failure and the acute coronary syndromes, unstable angina and acute myocardial infarction

Nitrates are potent venous dilators and anti-ischemic agents. They are widely used for the relief of chest pain and pulmonary congestion in patients with acute coronary syndromes and heart failure. Nitrates, however, do not reduce mortality in patients with acute coronary syndromes. Combination of nitrates and hydralazine when given in addition to beta-blockers and angiotensin-converting enzyme (ACE) inhibitors reduce mortality and heart failure hospitalizations in patients with heart failure due to left ventricular systolic dysfunction who are of African-American origin. Side effects during nitrate therapy are common but are less well described in the literature compared with the reported side effects in patients with stable angina pectoris. The reported incidence of side effects varies highly among different studies and among various disease states. Headache is the most commonly reported side effect with an incidence of 12% in acute heart failure, 41-73% in chronic heart failure, 3-19% in unstable angina and 2-26% in acute myocardial infarction. The reported incidence of hypotension also differs: 5-10% in acute heart failure, 20% in chronic heart failure, 9% in unstable angina and < 1-48% in acute myocardial infarction, with the incidence being much higher with concomitant nitrate therapy plus angiotensin-converting enzyme inhibitors. Reported incidence of dizziness is as low as 1% in patients with acute myocardial infarction to as high as 29% in patients with heart failure. Severe headaches and/or symptomatic hypotension may necessitate discontinuation of nitrate therapy. Severe life threatening hypotension or even death may occur when nitrates are used in patients with acute inferior myocardial infarction associated with right ventricular dysfunction or infarction, or with concomitant use of phosphodiesterase-5 inhibitors or N-acetylcysteine. Despite the disturbing observational reports in the literature that continuous and prolonged use of nitrates may lead to increased mortality and recurrent myocardial infarction in patients with stable coronary artery disease, no such adverse effects of nitrates have been reported in the large randomized trials in patients with acute myocardial infarction or chronic heart failure.

Contemporary management of acute coronary syndrome

This review focuses on the modern management of the non-ST elevation acute coronary syndromes (unstable angina and non-ST elevation myocardial infarction). Patients with these syndromes are at varying degrees of risk of (re)infarction and death. This risk can be reliably predicted by clinical, electrocardiographic, and biochemical markers. Aspirin, clopidogrel, heparin (unfractionated or low molecular weight), and anti-ischaemic drugs should be offered to all patients, irrespective of the predicted level of risk. Patients at high risk should also receive a glycoprotein IIb/IIIa receptor inhibitor and should undergo early coronary arteriography with a view to percutaneous or surgical revascularisation. Lower risk patients should undergo non-invasive testing. When inducible myocardial ischaemia is exhibited coronary arteriography should follow. When non-invasive testing is negative, a conservative management strategy is safe.

Nitroglycerin upregulates matrix metalloproteinase expression by human macrophages

OBJECTIVES

This study aimed to determine whether nitroglycerin (NTG) treatment affects matrix metalloproteinase (MMP) gene expression and activities in human macrophages.

BACKGROUND

Nitroglycerin is one of the most frequently used therapeutic agents for the symptomatic relief of stable or unstable coronary artery disease; however, its effects on vascular biology are poorly characterized. Despite its powerful vasodilator activity, NTG has not been shown to improve outcomes in coronary disease. We now describe evidence that NTG has potentially pro-inflammatory effects in human monocyte-derived macrophages (MDMs).

METHODS

Human monocytes were isolated from whole blood by elutriation and allowed to differentiate into macrophages over eight to 10 days. The MDMs were then treated for 4 or 24 h with control media, pharmacologically relevant doses of NTG or other nitric oxide donors. Matrix metalloproteinase activity was measured by zymography, protein levels measured by enzyme-linked immunosorbent assay and messenger ribonucleic acid (mRNA) levels were quantified by competitive reverse transcription-polymerase chain reaction.

RESULTS

The major MMP expressed by MDMs was MMP-9. Nitroglycerin treatment stimulated a dose-dependent increase in MMP-9 mRNA levels (NTG 200 pmol: 193 +/- 6% and NTG 2,000 pmol: 372 +/- 9% compared to controls, p < 0.005) and MMP-9 activity (NTG 200: 142 +/- 5.5% and NTG 2,000: 167 +/- 11% compared to controls, p < 0.005). Nitroglycerin 2,000 pmol also increased MMP-2 and MMP-7 mRNA levels to 187 +/- 8% and 183 +/- 21% of control values, respectively (p < 0.05). Furthermore, tissue inhibitor of metalloproteinase (TIMP)-1 (the major tissue inhibitor of MMPs) mRNA and protein levels were decreased in NTG 2,000 pmol-treated MDMs compared with control cells (mRNA: 67 +/- 7%, p < 0.005; protein: 45 +/- 5%, p < 0.005).

CONCLUSIONS

Nitroglycerin in pharmacologically relevant concentrations activates MMP but represses TIMP expression in human macrophages. The subsequent imbalance in MMP/TIMP expression associated with NTG treatment could promote matrix degradation, with potentially adverse effects on plaque stability.

The release of nitroglycerin absorbed into the central venous catheter

This study was conducted to evaluate the release of nitroglycerin (NG) that has been absorbed into the central venous catheter. A 0.05% NG solution was infused through a central venous catheter and the flow rates were set at 1, 5, or 10 ml/h, given over 12, 24, or 48 h. The catheter was flushed with lactate Ringer solution after completion of the NG infusion. The elution of the lactate Ringer solution from the tip of the catheter was then collected and assayed for its NG concentration by high performance liquid chromatography (HPLC). A higher concentration of NG was released with a faster flow rate and a longer infusion. The high level of NG release continued during the first 20 min, and ranged from a minimum of 0.07 mg/ml to a maximum that exceeded 0.15 mg/ml. Subsequently, the NG concentration gradually declined, but low concentrations of 0.006-0.02 mg/ml were still maintained 360 min later. Thus, it is suggested that if a catheter such as the Swan-Ganz continues to be used after the completion of a NG infusion, certain pharmacological effects due to the absorption of NG into the catheter body should be expected for at least 60 min.

Randomized trial comparing intravenous nitroglycerin and heparin for treatment of unstable angina secondary to restenosis after coronary artery angioplasty

BACKGROUND

The treatment of unstable angina targets the specific pathophysiological thrombotic process at the site of the active culprit lesion. In unstable angina due to a restenotic lesion, smooth muscle cell proliferation and increased vasoreactivity may play a more important role than thrombus formation. Therefore, the relative benefits of nitroglycerin and heparin might differ in unstable angina associated with restenosis compared with classic unstable angina.

METHODS AND RESULTS

We randomized 200 patients hospitalized for unstable angina within 6 months after angioplasty (excluding those with intracoronary stents) to double-blind administration of intravenous nitroglycerin, heparin, their combination, or placebo for 63+/-30 hours. Recurrent angina occurred in 75% of patients in the placebo and heparin-alone groups, compared with 42.6% of patients in the nitroglycerin-alone group and 41.7% of patients in the nitroglycerin-plus-heparin group (P<0.003). Refractory angina requiring angiography occurred in 22.9%, 29.2%, 4. 3%, and 4.2% of patients, respectively (P<0.002). The odds ratios for being event free were 0.24 (95% CI, -0.13 to 0.45, P=0.0001) for nitroglycerin versus no nitroglycerin and 0.98 (95% CI, -0.55 to 1. 73, P=NS) for heparin versus no heparin. No patient died or suffered myocardial infarction.

CONCLUSIONS

Intravenous nitroglycerin is highly effective in preventing adverse ischemic events (recurrent or refractory angina) in patients with unstable angina secondary to restenosis, whereas heparin has no effect.

High-dose nitrates in the immediate management of unstable angina: optimal dosage, route of administration, and therapeutic goals

Nitrates are commonly used for rapid relief of ischemia in the initial management of unstable angina. However, their optimal dosage, route of administration, and therapeutic goals have not been fully established. This study was conducted to determine the optimal dosage and mode of administration (intravenous bolus versus sublingual spray) of nitrates and the therapeutic goals of their use in the immediate management of unstable angina. In a single-center prospective trial, 72 consecutive patients with unstable angina accompanied by typical ST-segment depression on electrocardiogram were randomly assigned to receive isosorbide dinitrate either as repeated intravenous boluses or as sublingual sprays while being delivered to the hospital by a mobile intensive care unit. Optimal nitrate dosage was tailored to pain relief while monitoring mean blood pressure reduction to an optimal range (5% to 20%) without dosage restriction. The mean nitrate dosage needed for ischemia control during the first hour of treatment was 7.8 +/- 3.8 mg. Optimal blood pressure reduction was achieved by significantly more intravenously treated patients than sublingually treated patients (68% v 41%, P = .037). Intravenously treated patients also experienced a more pronounced therapeutic effect, as assessed by reduction in chest pain score (67% v 39%, P = .0004) and decrease in ST-segment depressions (57% v 27%, P = .004). These results show that higher doses of nitrates than previously recommended are required for ischemia control during the initial management of unstable angina. The use of repeated intravenous boluses is safe and more easily controlled and, therefore, more efficacious than sublingual sprays in inducing the maximal anti-ischemic effect while avoiding significant hypotension.

Effects of prior aspirin and anti-ischemic therapy on outcome of patients with unstable angina. TIMI 7 Investigators. Thrombin Inhibition in Myocardial Ischemia

Both aspirin and beta-adrenergic blocking drugs have been shown to reduce the risk of death or acute myocardial infarction (AMI) in patients with unstable angina, but their effect during chronic use on the presentation of acute coronary syndromes is less well defined. Calcium antagonists and oral nitrates are also widely prescribed for patients with coronary disease, but their effect on presentation of acute myocardial ischemia is unknown. We retrospectively examined the effects of prior aspirin and anti-ischemic medical therapy on clinical events in 410 patients hospitalized for unstable angina. Ischemic pain occurred at rest for a duration of 5 to 60 minutes. During hospitalization, 97% of patients received aspirin and all received the direct thrombin inhibitor bivalirudin for at least 72 hours. Despite being older and more likely to have risk factors for coronary disease and poor outcome, patients receiving aspirin before admission were less likely to present with non-Q-wave AMI (5% vs 14% in patients not on aspirin, p = 0.004). Prior beta blocker, calcium antagonist, or nitrate administration did not appear to modify presentation as unstable angina or non-Q-wave AMI. In a multivariate model, the combined incidence of death, AMI not present at enrollment, or recurrent angina was best predicted by age (adjusted odds ratio [95% confidence interval] 2.38 [1.14 to 3.98]) and presence of electrocardiographic changes with pain on presentation (adjusted odds ratio 2.83 [1.50 to 5.35]) but was not related to prior or in-hospital medical therapy. Thus, aspirin but not anti-ischemic therapy before hospitalization of patients with unstable angina was associated with a decreased incidence of non-Q-wave AMI on admission.

Intravenous nitroglycerin reduces ischaemia in unstable angina pectoris: a double-blind placebo-controlled study

OBJECTIVE

To study whether intravenous nitroglycerin (NTG) reduces the incidence of ischaemic events and leucocyte activation, as well as inhibiting platelet aggregation in patients with unstable angina pectoris.

DESIGN

Randomized double-blind placebo-controlled study.

SUBJECTS

One hundred and sixty-two patients with a history and electrocardiographic changes suggesting unstable angina pectoris.

INTERVENTIONS

A 48-hour titrated intravenous infusion of NTG or placebo.

RESULTS

Of the 162 randomized patients, 19 were excluded because of an acute myocardial infarction on randomization (11 patients) or proven presence of a non-ischaemic cause of the pain (6 patients). Other causes (2 patients). No differences in the clinical findings were detected between the groups on randomization. In the comparison of NTG and placebo, fewer patients in the former group had more than two new attacks of chest pain lasting for < 20 min or one new attack of chest pain lasting > 20 min, despite sublingual NTG (13/25, P < 0.03). In addition, the attacks of pain lasting > 20 min in the NTG group were delayed compared to those in the placebo group (P < 0.05), suggesting a beneficial effect on these more severe episodes. Fewer patients in the NTG group required more than two sublingual NTG tablets (P < 0.005). NTG also reduced the rate-pressure product (P < 0.05), compared to placebo after 2 h but not after 24 h. Compared to baseline, platelet aggregation was inhibited in the patients who had received an NTG infusion for 2 h (P < 0.05). In both groups, leucocytes were activated at baseline, but remained unchanged thereafter.

CONCLUSIONS

Intravenous NTG seems to reduce myocardial ischaemia in patients with unstable angina pectoris more than the placebo.

Persistent inhibition of platelets during continuous nitroglycerin therapy despite hemodynamic tolerance

BACKGROUND

Nitroglycerin has been shown to possess antiplatelet properties in both animals and humans. Tolerance to the hemodynamic effects of nitroglycerin develops with continuous therapy, but it is unclear whether there is tolerance to its antiplatelet effect.

METHODS AND RESULTS

Tolerance to nitroglycerin was studied by exposing porcine aortic media to flowing arterial blood from control pigs (n = 9) or pigs treated with continuous nitroglycerin patches (Nitro-dur, 0.8 mg/h; n = 11) at a shear rate of 3397 s-1 for 3 minutes. Relative to baseline, mean arterial pressure fell by approximately 10% at 3 and 24 hours (P < .05) but returned to baseline at 48 hours of continuous nitroglycerin treatment, whereas no significant changes were observed in control animals. Autologous 51Cr-labeled platelet deposition (x 10(6)/cm2) on the aortic media at baseline and 3, 24, and 48 hours remained stable in control animals, with mean values of 94.8 +/- 5.9, 89.4 +/- 8.3, 89.3 +/- 8.8, and 84.3 +/- 5.7, respectively. However, in pigs treated continuously with nitroglycerin for 48 hours, platelet deposition was reduced significantly at 3 (65.9 +/- 4.8), 24 (63.8 +/- 6.4), and 48 hours (56.5 +/- 7.3) of nitroglycerin treatment compared with baseline (93.1 +/- 3.6). Platelet aggregation induced by thrombin also decreased at 3 (12.4 +/- 1.3), 24 (12.6 +/- 1.7), and 48 hours (10.8 +/- 1.6) of nitroglycerin treatment compared with baseline (16.3 +/- 1.4) but remained unchanged in the control group. Also, nitroglycerin treatment increased intraplatelet cGMP at 3, 24, and 48 hours compared with baseline.

CONCLUSIONS

This study demonstrates the persistent inhibition of platelet function and platelet deposition on an injured arterial wall by continuous nitroglycerin therapy despite hemodynamic tolerance.

Platelet activation in acute myocardial infarction and unstable angina is inhibited by nitric oxide donors

Platelet activation and thrombus formation within the coronary artery are major factors in acute myocardial infarction (AMI) and unstable angina (UA), and continuing platelet activation is associated with an adverse prognosis. We assessed platelet activation by using flow cytometry to measure platelet surface expression of P-selectin and glycoprotein IIb/IIIa in 20 patients with AMI and 20 with UA, all of whom were treated with aspirin. Platelet studies were repeated after the infusion of a nitric oxide donor (glyceryl trinitrate or S-nitrosoglutathione) that produced a fall in mean arterial pressure of no more than 10 mm Hg. P-selectin was expressed on 2.5% (range, 1.4% to 6.3%) of platelets from AMI and 2.3% (range, 1.6% to 3.3%) from UA subjects compared with 1.0% (range, 0.6% to 1.9%) of platelets from 20 control volunteers without angina (P < .001). Glycoprotein IIb/IIIa expression was 101.6 +/- 2.7 arbitrary units of relative fluorescence in AMI and 100.2 +/- 3.3 in UA compared with 87.8 +/- 2.5 in control subjects (P < .01). In both AMI and UA, S-nitrosoglutathione reduced P-selectin (P < .001) and glycoprotein IIb/IIIa (P < .05) expression, as did glyceryl trinitrate (P < .02 and P < .01, respectively). In 3 of 20 patients receiving glyceryl trinitrate the lowest dose was not tolerated due to headache or hypotension. These findings show that platelet activation persists in AMI and UA despite aspirin treatment and that this can be inhibited by using glyceryl trinitrate or S-nitrosoglutathione. S-nitrosoglutathione is better tolerated at the doses required.

Randomised, double-blind trial of intravenous diltiazem versus glyceryl trinitrate for unstable angina pectoris

The effect of dihydropyridines in patients with unstable angina is discouraging. To find out the effect of the non-dihydropyridine-like calcium-channel blocker diltiazem, a randomised, double-blind trial was conducted comparing diltiazem with glyceryl trinitrate, both given intravenously, in 129 patients with unstable angina. The endpoints were refractory angina or myocardial infarction, individually and as a composite endpoint. Refractory angina alone or together with myocardial infarction occurred significantly less commonly in the diltiazem group. While patients were on the trial drugs the numbers with refractory angina were 6 (10%) in the diltiazem group versus 17 (28%) in the glyceryl trinitrate group (relative risk 0.36, p = 0.02), and the numbers with refractory angina and myocardial infarction were 9 (15%) versus 23 (38%) (relative risk 0.40, p = 0.007). Over 48 h the number were: refractory angina 8 (13%) versus 18 (30%), relative risk 0.45, p = 0.03, and refractory angina and myocardial infarction 12 (20.0%) versus 25 (41%), relative risk 0.49, p = 0.02. Patients in the diltiazem group had better (p < 0.05) event-free survival while taking the drugs. Heart-rate pressure product was reduced significantly only by diltiazem (p < 0.05). The incidence of bradyarrhythmias did not differ significantly. Atrioventricular conduction disturbances occurred in 5 (8%) patients in the diltiazem group but were not seen in the glyceryl trinitrate group (p = 0.03). These disturbances could be reversed by decreasing the dose of the drug or withdrawing it. No temporary pacemakers were required. Headache requiring an analgesic or dose adjustment occurred significantly less in the diltiazem group: 3 (5%) versus 15 (25%), relative risk 0.20 (p < 0.004). These results indicate that intravenous diltiazem, compared with intravenous glyceryl trinitrate, significantly reduces ischaemic events and can be used safely in patients with unstable angina.

A clinical and in vitro study on the possible interaction of intravenous nitrates with heparin anticoagulation

It has been reported that intravenous nitrates inhibit the anticoagulant effect of heparin. This possible interaction has potentially serious implications for the management of patients with acute coronary ischemic syndromes. This possible interaction was assessed prospectively in a clinical and in an in vitro study involving 24 patients receiving both drugs for the management of unstable angina pectoris. There was a small inhibitory effect of intravenous glyceryl trinitrate or isosorbide dinitrate on the anticoagulant effect of heparin in 3 of 24 cases in vivo, as assessed by activated partial thromboplastin time measurements. Nitrates or propylene glycol had no effect on heparin activity in vitro. It was concluded that there may be an inhibitory effect of nitrates on anticoagulation in a small minority of patients, but close attention to detail in monitoring heparin anticoagulation is far more important.

Nitrates for unstable angina

The term unstable angina encompasses heterogeneous clinical syndromes. Fissuring of an atherosclerotic coronary artery plaque with superimposed platelet deposition, with or without additional thrombus formation, is invariably responsible for a prolonged episode of angina at rest, increasing frequency of angina at rest, or with minimal exertion of less than 4 weeks in duration and early postinfarction angina. Plaque progression, rather than plaque fissuring, is the most likely mechanism for progressive reduction in walking distance due to angina in patients who previously have stable angina. Coronary artery spasm is responsible for Prinzmetal's variant angina, but its exact role in other forms of unstable angina is unknown. The mainstay of treatment of unstable angina (prolonged episode of angina at rest and recent onset angina at rest, or with minimal exertion with a crescendo pattern) is aspirin, heparin, or both. Both aspirin and intravenous (i.v.) heparin or their combination reduce early mortality and the incidence of acute myocardial infarction in patients hospitalized with unstable angina. However, these agents do not promptly relieve chest pain. There are no placebo-controlled studies evaluating the usefulness of nitrates in unstable angina. In open-label studies, continuous therapy with i.v. nitroglycerin (NTG) for 24 hours or longer has been shown to relieve chest pain in patients with rest angina refractory to therapy with other antianginal agents, including long-acting nitrates. Recurrence of chest pain in patients receiving i.v. NTG is a common problem and probably represents development of pharmacologic tolerance, but this can be overridden by dose escalation; protracted tolerance during short-term use of i.v. NTG is usually not a problem.(ABSTRACT TRUNCATED AT 250 WORDS)

Bolus i.v. nitroglycerin treatment of ischemic chest pain in the ED

A prospective case series was conducted to demonstrate the safety and efficacy of intravenous nitroglycerin (i.v. NTG) boluses in the treatment of ischemic chest pain (CP) in the emergency department (ED). Patients with CP symptomatic after sublingual nitroglycerin (SL NTG) therapy with a systolic blood pressure (SBP) greater than 95 mmHg were included. Patients were treated with i.v. NTG boluses of 0.05 mg to 0.4 mg during a 1- to 2-minute period per a protocol based on the patient's prebolus SBP. This was followed by a maintenance infusion. Additional NTG boluses were repeated every 5 minutes as needed. The end point of treatment was the resolution of chest discomfort, thrombolysis, or a SBP less than 95 mmHg. There were 16 cases of CP. All 16 patients treated, ie, 5 with acute myocardial infarction and 11 with unstable angina showed significant decrease in chest discomfort after 1 to 2 boluses. Two of five with acute myocardial infarction and 9 of 11 patients with unstable angina had complete relief of chest pain after 1 to 4 boluses. There were no episodes of hypotension (SBP < 90 mmHg) in any of the 16 cases. The judicious use of i.v. NTG boluses administered during a 1- to 2-minute period, in the ED, appears safe and efficacious in patients with CP unresponsive to SL NTG therapy.

The effect of different nitrate preparations on plasma heparin concentrations and the activated partial thromboplastin time

There is evidence that intravenous nitrates which are frequently used in acute coronary syndromes may interfere with the anticoagulant effect of heparin. We compared the effect of two different nitrate preparations on the activated partial thromboplastin time (APTT), anti-thrombin III activity (AT III) and plasma heparin levels in patients (n = 50) undergoing routine percutaneous transluminal coronary angioplasty (PTCA) for stable angina. Patients were randomized to either: (1) intravenous heparin and nitroglycerin (GTN); or (2) intravenous heparin and isosorbide dinitrate. The APTT, plasma heparin concentration and AT III activity were measured before PTCA and at 2 and 4 hours after commencement of infusions. Both groups received identical doses of heparin. Group 1 patients received a constant dose of 16.6 micrograms/minute of GTN, and group 2 patients received 33.3 micrograms/minute of isosorbide dinitrate. At 4 hours the median APTT ratio was significantly lower in group 1 compared with group 2 (2.6 versus 4.5) (P < 0.05) as was the plasma heparin concentration (0.18 U/ml versus 0.32 U/ml (P < 0.05). However, no significant difference in APTT ratios or plasma heparin concentrations were noted at any of the other sample times. AT III activity was not significantly different between the groups at any sample time. Within-group analysis showed significantly lower APTT ratio and heparin concentrations at 4 hours compared with the respective 2 hour values. These results would suggest that there is a potential impairment of anticoagulation with low-dose intravenous nitroglycerin and to a lesser extent with low-dose isosorbide dinitrate. Early and frequent monitoring may therefore be appropriate when intravenous nitrates and heparin are used in combination.

Role of nitrates in unstable angina pectoris

Unstable angina pectoris is a clinically heterogeneous process with patient symptoms varying between reduced threshold for exertional angina and the occurrence of multiple episodes of rest pain. The major factors in the pathogenesis of unstable angina appear to be intracoronary platelet aggregation and thrombus formation secondary to fissuring or rupture of atheromatous plaques, with associated coronary vasoconstriction due to release of constrictor materials from aggregating platelets and deficiency of endothelium-related vasodilator activity. The latter factor is of particular interest in view of the similar biochemical mechanisms of action of nitroglycerin (NTG) and endothelium-derived relaxing factor (EDRF). The efficacy of NTG in limiting platelet aggregation is also of particular interest in this condition. Medical therapy in patients with unstable angina usually requires use of multiple agents. In the short term, there is a strong case for the use of intravenous heparin both to relieve pain and to reduce the risk of acute myocardial infarction. Aspirin is perhaps less effective in the short term, but very useful in long-term treatment of such patients. Despite their widespread clinical use, beta-adrenoceptor antagonists are probably only marginally beneficial, whereas dihydropyridine calcium antagonists such as nifedipine are potentially harmful as monotherapy and of questionable use in combination with other drugs. Other agents that are effective in relieving ischemic symptoms are the nondihydropyridine calcium antagonists verapamil and diltiazem and the oxygen-sparing agent perhexiline maleate. Despite a paucity of controlled trial data, nitrates are used in the vast majority of patients with unstable angina.

Use of nitrates in ischemic heart disease

The organic nitrates have remarkably diverse actions that are or should be beneficial in patients with ischemic heart disease. These drugs are effective in all the important ischemic syndromes. Preliminary data in patients with acute infarction suggest that the drugs may be truly cardioprotective, resulting in improved mortality. This review has not discussed the role of nitrates in congestive heart failure or LV dysfunction, a subject of great importance. The nitrates are useful adjunctive agents in these syndromes, and the two VeHfT trials support the concept that long-term nitrate administration, in conjunction with hydralazine, may favorably alter the natural history of heart failure. This cardioprotective effect is similar to that suggested for the post-MI patient. The data are not strong enough for definitive conclusions at this time. The clinical benefits of nitrates in decreasing subjective (angina) and objective indices of ischemia in stable and unstable angina, as well as limited data in asymptomatic myocardial ischemia, are unequivocal and are as favorable as those for beta blockers or calcium antagonists. Tolerance is an important problem that unfavorably influences the potential benefits of nitrate therapy. I believe that this problem can be avoided with well-designed dosing regimens. Current research into endothelial biology in health and disease has further supported a physiologic role for the organic nitrates in patients with ischemic heart disease. The nitrate-platelet story, while controversial, is promising and offers another positive rationale for nitrate administration. The concept of nitrates replenishing disordered EDRF release or action is an exciting one. Physicians should feel fortunate to have such a remarkable group of drugs available for their patients.

Pharmacotherapy of unstable angina

All patients with unstable angina should be admitted to a coronary or an intensive care unit. There should be an attempt to classify the patient according to the proposed Braunwald nomenclature. If the patient has a secondary cause for unstable angina (e.g., tachyarrhythmia, heart failure, fever, thyrotoxicosis, severe hypertension, hypoxia, unusual emotional stress, or anemia), this condition should be treated initially with therapy specific for that etiology. If the patient does not have a secondary etiology, therapy should be initiated with nitrates, preferably intravenous nitroglycerin. Heparin should be concomitantly administered. If the patient cannot receive heparin, aspirin should be initiated. All patients should receive beta-blockers. If the patient cannot take a beta-blocker, a calcium antagonist (probably diltiazem) should be initiated. However, if the patient is refractory to beta-blockers, the dihydropyridine nifedipine should be added. Failure to all pharmacologic interventions necessitates a progressive invasive approach dictated by the potential surgical risk of the patient. Long-term aspirin and beta-blockers should be strongly considered.

Treatment of unstable angina pectoris (European experience)

Unstable angina pectoris is used to describe accelerated angina, new onset of angina, or prolonged angina. The natural history of the angina varies according to clinical presentation. The 1-year mortality rate ranges from 2% to nearly 40%. Specific therapy includes nitrates, beta-adrenergic blockers, and/or calcium antagonists as well as antithrombotic therapy in the form of aspirin. Patients with severe angina at rest and ST- and T-wave changes should be admitted to a coronary care unit where full-dose heparin is administered. Coronary angiography should be performed in individuals who fail to respond to the conventional therapy in order to evaluate other therapeutic options, including percutaneous transluminal coronary angioplasty (PTCA) and coronary bypass surgery. In some cases, especially in patients with intracoronary thrombus, thrombolytic therapy may be beneficial.

Dynamics of coronary occlusion in the pathogenesis of myocardial infarction

In most coronary artery stenoses in humans, lumen size decreases in response to acute vasoconstriction, reduced aortic pressure or passive collapse. Because the effects of vasoconstriction and plaque rupture with thrombus formation are additive, in some cases total cessation of flow may result from only minimal obstruction by thrombus. This hypothesis was investigated with use of a previously developed model of the coronary circulation in which the pressure drop across and flow through an arterial stenosis were determined by standard hemodynamic equations. The vessel wall was assumed to be composed of pliable and rigid sections, as is the case in most arterial stenoses in humans. The computer analysis was conducted for a rigid stenosis and for a dynamic stenosis in which proximal artery constriction and distal collapse were simulated. Plaque rupture with subsequent thrombus formation was simulated as a decrease in lumen area without effect on the arterial wall. Compared with a dynamic stenosis, a rigid stenosis required a significantly larger thrombus for vessel occlusion. Thrombus formation equal to the nonobstructed area of the lumen was required to occlude a rigid vessel; a 60% stenotic vessel required a 40% plaque rupture with thrombus formation for occlusion. However, for a dynamic stenosis, if vasoconstriction and passive collapse were simulated, small plaque ruptures led to vessel occlusion: a 60% stenotic vessel required only a 12% plaque rupture with thrombus formation for occlusion. This analysis indicates that even mild coronary lesions may be responsible for myocardial infarction, suggesting that vasomotion may be a very important element in the pathogenesis of most myocardial infarcts.

Buccal versus intravenous nitroglycerin in unstable angina pectoris

The clinical syndrome of unstable angina includes patients with the first onset of angina, change in a previous stable pattern or the development of chest pain at rest. Administration of intravenous nitroglycerin is established therapy in unstable angina. Buccal nitroglycerin has been introduced as an alternative means of administering nitroglycerin, which provides relief of anginal pain within 2 to 3 min and a sustained effect for 3 to 5 h. Twenty-nine patients admitted to the coronary care unit due to unstable angina were randomized to receive treatment with nitroglycerin i.v. for 24 h or buccal nitroglycerin every 4 h. Therapy was titrated according to haemodynamic effects. The mean dose of buccal nitroglycerin was 4.42 mg versus 0.45 micrograms.kg-1.min-1 in the intravenous group. The efficacy of treatment was similar in the two groups. Buccal nitroglycerin appeared to cause fewer adverse effects, especially less haemodynamic intolerance and headache, although the differences were not significant. Repeated administration of buccal nitroglycerin appears to be a safe and well tolerated alternative to high-dose i.v. nitroglycerin treatment in unstable angina pectoris.

Effects of nitroglycerin at therapeutic doses on platelet aggregation in unstable angina pectoris and acute myocardial infarction

The platelet aggregation response to adenosine diphosphate (ADP) and to thrombin was quantified in 10 patients, 5 with unstable angina pectoris and 5 with acute myocardial infarction, before, during and after a 45-minute infusion of nitroglycerin. An impedance aggregometer allowing rapid bedside studies in whole blood was used. The reproducibility of the methods was documented to be within 10%. Doses of nitroglycerin were titrated for a 10 mm Hg decrease in mean arterial blood pressure with mean doses being 1.2 +/- 0.2 (standard error of the mean) micrograms/kg/min. Nitroglycerin decreased the area under the aggregation curve induced by ADP from 43 +/- 3.6 to 30 +/- 6.3 cm2 (p = 0.007) and by thrombin from 8.9 +/- 1.7 to 4.1 +/- 0.9 cm2 (p = 0.003). Peak responses to ADP were decreased from 13.3 +/- 1 to 9.1 +/- 1.7 ohms (p = 0.005) and to thrombin from 9.3 +/- 2 to 5.0 +/- 1.2 ohms (p = 0.003). All patients had greater than or equal to 50% inhibition with 1 agent or the other and the inhibition was greater than 50% with each of the 2 aggregating agents in 6 patients. Analyses performed on blood withdrawn 15 minutes after the discontinuation of nitroglycerin showed a return to baseline before nitroglycerin results. When analyses were delayed and performed on blood preserved at room temperature for 30 minutes, no effect of nitroglycerin could be detected. Thus, bedside platelet aggregation studies document a significant and reversible effect of nitroglycerin at therapeutic doses on platelet function.

Coronary angioplasty for medically refractory unstable angina in patients with prior coronary bypass surgery

Percutaneous transluminal coronary angioplasty (PTCA) has been applied with good results to selected patients with unstable angina and to selected patients who have had prior bypass surgery. The population with prior bypass and unstable angina has not been specifically evaluated. This report reviews the results of angioplasty of 45 vessels in 34 patients with medically refractory unstable angina and at least one prior bypass heart surgery. Of these 34 patients, 32 had rest angina; 14 had resting electrocardiographic changes, all 34 were on aspirin 325 mg QD, 31 were on a calcium blocker, 22 were on a beta blocker, 9 were on intravenous nitroglycerin, and 5 required intraaortic balloon counterpulsation for temporary stabilization. Angioplasty of a vein graft was attempted in 17 patients; the left internal mammary was attempted in 4 patients; 24 native coronary arteries in 15 patients were attempted; 3 of the native arteries were protected left main arteries. Of the LIMA angioplasties, 3 were successful; in the 1 unsuccessful case, the occluded anterior descending artery was opened. Of the 17 vein grafts, 16 were successful: 1 had an acute occlusive syndrome and went to surgery with a balloon pump and bail out catheter; his recovery was uneventful. Of the 24 native artery angioplasties, 22 were successful: one patient was technically unsuccessful in the only vessel attempted; he went to semiemergent surgery and recovered uneventfully. In the other, a right coronary lesion was successfully dilated, but an occluded anterior descending artery was not opened. There were no deaths or in-hospital myocardial infarctions.(ABSTRACT TRUNCATED AT 250 WORDS)

Unstable angina

Unstable angina can manifest as an array of symptom complexes. In some patients, medical therapy will stabilize the episodes of angina, and only predismissal exercise testing or angiography (or both) will be necessary. At the other end of the spectrum are patients with rest angina or multiple episodes of silent ischemia who are refractory to medical therapy and experience undetected microinfarction. Most of these patients require immediate catheterization and subsequent intervention with intra-aortic balloon pulsation, percutaneous transluminal coronary angioplasty, or coronary artery bypass grafting. An entire spectrum of manifestations exists between these two extremes. One challenge during the 1990s will be better stratification of patients with unstable angina so that safe, efficient, cost-effective treatment strategies can be appropriately applied to all patients.

Does nitroglycerin induce heparin resistance?

We studied the possibility that intravenous nitroglycerin may produce heparin resistance both in vitro and prospectively in a group of 10 patients following coronary angioplasty. Nitroglycerin in physiologic to pharmacologic concentrations (41-250 micrograms/ml) did not produce heparin resistance in vitro as measured by activated partial thromboplastin time and thrombin time. The maximum reduction in activated partial thromboplastin time was 7%. In patient studies, the activated partial thromboplastin time at baseline on heparin alone (93 + 22 s) was not significantly different (p = 0.61) from activated partial thromboplastin measured upon addition of nitroglycerin (94 +/- 27 s) or 30 min following cessation of the nitroglycerin infusion while continuing the same dose of heparin (91 +/- 24 s). We conclude that intravenous nitroglycerin does not induce heparin resistance in vitro or in patients during short-term administration.

Treatment of pain in acute myocardial infarction

The treatment of pain in acute myocardial infarction varies with local practice. Narcotic analgesics are still the usual treatment in many hospitals. Knowledge of optimal doses, duration of pain relief, and time between drug administration and pain relief is inadequate. Many studies indicate that the relief of pain is often incomplete after treatment with narcotic analgesics. There is often a need for alternative treatments. Large randomised studies consistently show that beta blockade, initially given intravenously and then orally, relieves pain and reduces the need for analgesics. Studies also indicate that early administration of streptokinase and glyceryl trinitrate relieves pain. There is evidence that drugs that limit ischaemic damage also relieve pain.

Clinical characteristics and coronary anatomy in refractory unstable angina pectoris leading to coronary artery bypass grafting. The Kuopio experience

One hundred patients with high-risk unstable and medication-resistant angina pectoris underwent coronary artery by-pass grafting. In 35 cases the angina was of early post-infarction type, in 60 it was progressive after previous stability and in five it was of recent onset. All had abnormal ECG in association with anginal attacks (ST depression in 76, ST elevation in 5, T-wave inversion in 15 and left bundle branch block in 4). The left main coronary artery was stenosed in 33 patients, and the respective figures for three-vessel, two-vessel and one-vessel disease were 53, 9 and 5. The average number of inserted peripheral grafts/patient was 4.6. The perioperative mortality rate was 1%. Seven patients had confirmed or probable perioperative myocardial infarction and two had late infarction during the hospital stay, but none had angina pectoris on discharge. Of 60 patients re-examined after 1 year, 47 were angina-free. Five had NYHA class III angina, but all were improved. In refractory unstable angina pectoris there is severe coronary artery involvement, but bypass grafting can give good results.

Unstable angina: current concepts of medical management

Unstable angina describes a clinical syndrome bridging the gap between stable angina and acute myocardial infarction. By definition, patients with angina of new onset, of a crescendo pattern, and with angina at rest are included in this high-risk group. The underlying pathogenetic mechanisms are complex and include initial atherosclerotic plaque rupture, release of vasoactive substances, and intracoronary thrombus formation. The currently established medical approach of the acute phase consists of heparin for anticoagulation and nitrates combined with beta-blockers for the relief of pain. Calcium antagonists are indicated, if anginal symptoms persist. The effect of thrombolytic therapy is still under investigation. Angina refractory to medical treatment and angina at rest are associated with a particularly unfavorable prognosis and prompt early catheterization. The long-term prognosis of the patient is markedly improved by chronic platelet inhibitory treatment with aspirin.

Usefulness of serial radionuclide monitoring during graded nitroglycerin infusion for unstable angina pectoris for determining left ventricular function and individualized therapeutic dose

Using serial invasive hemodynamics in concert with noninvasive radionuclide monitoring of left ventricular (LV) function, 20 patients with unstable angina were evaluated during incremental infusion of intravenous nitroglycerin. Of 20 patients, 17 demonstrated a favorable hemodynamic response and dose responses could be determined for individual patients. There was excellent agreement between hemodynamic and noninvasive radionuclide measurements, and patient responses could be inferred from the radionuclide data alone. Cardiac output improved by 29% (mean 4.7 +/- 1.2 to 6.0 +/- 1.3), LV ejection fraction increased an average of 0.11 (0.39 +/- 0.14 to 0.50 +/- 0.16) and diastolic function as assessed by peak filling rate improved from 1.80 +/- 0.60 end-diastolic volumes/s to 2.70 +/- 0.90. Changes in systolic blood pressure and heart rate were not predictive of hemodynamic response. The dose of nitroglycerin necessary to produce maximal hemodynamic benefit was variable (mean 98 micrograms/min, range 48 to 144). In 7 patients, nitroglycerin caused excessive decreases in pulmonary arterial wedge pressure and adverse hemodynamics that corrected with intravenous fluids, allowing continued administration of intravenous nitroglycerin with improvement in hemodynamic status. In 15 patients, peak systolic pressure--end-systolic volume relations were assessed to define possible changes in LV contractility induced during nitroglycerin infusion. In 12 of these patients, this relation was linear, suggesting altered loading rather than augmented contractility as nitroglycerin's mechanism of action. In 3 patients a downward and rightward shift of the systolic relation was seen, suggesting that significant underloading with nitroglycerin was associated with depressed contractility.