Physiologic and clinical actions of nitroglycerin

Nonischemic Causes of Cardiogenic Shock

Although cardiogenic shock is uncommon in the emergency department, it is associated with high mortality. Most cardiogenic shock is caused by ischemia, but nonischemic etiologies are essential to recognize. Clinicians should optimize preload, contractility, and afterload. Volume-responsive patients should be resuscitated in small aliquots, although some patients may require diuresis to improve cardiac output. Vasopressors are important to restore end-organ perfusion, and inotropes improve contractility. Intubation and positive pressure ventilation impact hemodynamics, which, depending on volume status, may be beneficial or deleterious. Knowing indications for mechanical circulatory support is important for timely consultation or transfer as indicated.

Vasodilators in acute heart failure

Most patients with acute heart failure present with increased left ventricular filling pressure and high or normal blood pressure; only a minority present with cardiogenic shock. In this context, therapy with vasodilators in the acute setting can improve both hemodynamics and symptoms. Vasodilators are usually given in conjunction with diuretics, although much of the acute effect of loop diuretics may be due to venodilation. Currently available agents include nitroglycerin, nitroprusside, and nesiritide. Nitroglycerin relieves pulmonary congestion primarily through direct venodilation, but may dilate coronary arteries and increase collateral blood flow at higher doses, an effect desirable in patients with ischemia. Tachyphylaxis may develop, necessitating incremental dosing. The major adverse effects of nitrates are hypotension and headache. Nitroprusside is a balanced arterial and venous vasodilator with a very short half-life, facilitating rapid titration. Afterload reduction lowers blood pressure and can increase stroke volume. The major complications of nitroprusside therapy are hypotension, and toxicity from accumulation of cyanide or thiocyanate, usually in patients with renal insufficiency treated for more than 24 h. Nesiritide, a recombinant form of human B-type natriuretic peptide (BNP), is a venous and arterial vasodilator that may also potentiate the effect of concomitant diuretics. Hypotension is the most common side effect. In addition, meta-analyses have suggested that nesiritide may worsen renal function and decrease survival at 30 days compared to conventional therapies. Resolution of these concerns awaits completion of appropriately powered prospective clinical trials. Angiotensin-converting enzyme (ACE) inhibitors have vasodilatory effects, but intravenous infusion of enalapril within 24 h of ischemic chest pain is not recommended. Oral ACE inhibition may be used to reduce afterload in other settings if blood pressure permits. Use of calcium antagonists in acute heart failure is not recommended.

Transdermal glyceryl trinitrate (nitroglycerin) in healthy persons: acute effects on skin temperature and hemodynamic orthostatic response

In order to find an explanation for individual reactions to transdermal glyceryl trinitrate (GTN) we studied the skin temperature and hemodynamic reactions in 63 healthy persons. The data were obtained before and after the application of GTN and Glycerin (GL) placebo patches, during one hour. The skin temperature was measured on both forearms, the local (left sided) and systemic (right sided) reaction on GTN was related to the skin fold and the calculated body fat content. The bilateral rise of skin temperature and its duration was higher and longer in obese than in lean persons mainly in obese women. The UV induced thermo and the later photothermoreaction (Erythema) was reduced on the left forearm after the application of GTN and GL patches. The observed hemodynamic GTN effect confirmed known postural reactions, such as decreased arterial pressure (delta mAP = -2.9%), increased heart rate (delta HR = +7.4%) and QTc prolongation (delta QTc = +4.9%) in upright position. An adverse drug effect with increased mean blood pressure (delta mAP = +12%) and increased heart rate (delta HR = +10.4%) mainly in supine position was observed in 11% of the participants, but only in men. Such a reaction was already described by Murell, 1879. Individual GTN effects were analyzed and related to habits and family history. In male smokers and in persons with hypertensive and diabetic close relatives, the hypotensive GTN effect was accentuated in supine position. In the upright position the group with hypertensives in the family presented a moderate hypotensive reaction without secondary tachycardia and the smokers presented only a slightly increased heart rate. Our observations suggest that individual reactions to transdermal glyceryl trinitrate (GTN) with its active component nitric oxide (NO) depends on physiological conditions, related to endogenous vasoactive substances, mainly the interaction with EDRF (the endogenous NO) and the activity of the Renin-Angiotensin System.

Efficacy of intermittent (eight hours off) transdermal nitrate therapy in stable angina

The efficacy of intermittent (16 h on/8 h off) transdermal nitrate therapy (0.4 mg/h) was assessed in 46 patients with chronic stable angina, all but one of whom were on concomitant beta-blocker and/or calcium antagonist therapy. The study was a randomised, double-blind placebo-controlled crossover with two consecutive 7-day treatment periods, conducted at two centres. Prior to entry into the study patients were screened for exercise test reproducibility and nitrate response. Patch efficacy was determined by maximal symptom limited treadmill stress testing (Bruce protocol) and subjective diary card data. Analysis of variance showed that active treatment significantly improved time to onset of angina (P < 0.001), time to 1 mm ST-segment depression (P < 0.001) and total exercise duration (P < 0.001) compared with placebo from 385.7, 310.8 and 458.1 s to 455.7, 385.2 and 497.1 s, respectively. Nitrate patch therapy significantly reduced diastolic and systolic blood pressures without significantly increasing resting heart rate. There was a marginal reduction in the incidence of angina attacks and sublingual nitroglycerine consumption during active treatment. We conclude that intermittent transdermal nitrate therapy significantly improves exercise tolerance in patients with chronic angina pectoris and that this improvement occurs in addition to conventional anti-anginal therapy.

A randomised double-blind crossover study of isosorbide mononitrate and nifedipine retard in chronic stable angina

In order to evaluate and compare the efficacy and safety of nifedipine retard and isosorbide-5-mononitrate as monotherapy in the treatment of stable angina, 18 patients with abnormal exercise electrocardiograms and angiographically proven coronary arterial disease were studied in a randomised placebo controlled double-blind crossover study comparing isosorbide 20 mg twice a day, sustained released isosorbide 40 mg once daily and nifedipine 20 mg twice a day each given for two weeks. Patients were assessed subjectively by counting the frequency of anginal attacks and glyceryl trinitrate consumed and objectively by maximal symptom-limited treadmill stress tests performed at "trough" therapeutic blood levels on the last day of each treatment period. There were no significant differences in all parameters between entry and run-out placebo. Compared to placebo, all three active treatments showed significant improvement in exercise time to 1 mm ST segment depression, amount of maximum ST segment depression and exercise duration. All three active treatments also significantly reduced the consumption of glyceryl trinitrate and frequency of anginal attacks. There were no significant differences between active treatments. Thus similar clinical improvements were produced by nifedipine retard and isosorbide, both being shown to be equally effective starting therapy for the treatment of patients with stable angina pectoris. Although anginal frequency was reduced by one third and exercise time increased residual symptoms and exercise ischaemia suggest that nifedipine retard and isosorbide may be more clinically useful in combination therapy. Neither demonstrated tolerance after two weeks of therapy.

Effect of theophylline on exercise-induced myocardial ischaemia

In a single-blind, placebo-controlled, randomised trial in 20 patients with stable angina pectoris, intravenous theophylline ethylenediamine (aminophylline), 7 mg/kg, increased the time to onset of angina by 46%, the heart-rate/blood-pressure product (an index of myocardial oxygen consumption) at 1 mm ST segment depression by 22%, and exercise duration by 24%. In a subsequent double-blind placebo-controlled trial in 8 patients a single oral dose of theophylline (375 mg) increased the time to onset of angina by 56%, the heart-rate/blood-pressure product at 1 mm ST segment depression by 22%, and the exercise duration by 35%. Infusion of theophylline ethylenediamine during angiography (10 patients) did not affect the diameter of epicardial coronary arteries. The beneficial effects of theophylline may be due to redistribution of coronary blood flow from non-ischaemic to ischaemic myocardium.

Postinfarction angina

In conclusion, the PIA patient is at high risk, with higher early as well as late mortality. The pathophysiology of PIA is complex and may vary from patient to patient. The concepts of ischemia at a distance and ischemia in the infarct zone have led to a better understanding of early PIA. Coronary spasm may play an important role in most PIA patients as in the general population of patients with angina pectoris. Medical therapy is efficacious in many, although it may on rare occasion aggravate myocardial ischemia. Urgent coronary arteriography is generally safe and should be performed as soon as possible for medically refractory PIA. CABG appears to be safe in experienced hands, but its timing must be individualized. The IABP should be reserved for more unstable patients for fear of vascular complications. Randomized controlled trials such as the BARI Trial will further compare PTCA with CABG.

Isosorbide dinitrate and exercise performance in patients with congestive heart failure

Nitrates are widely used for the management of congestive heart failure (CHF), as well as angina pectoris. In both situations, nitrates significantly increase exercise capacity. The mechanism of this beneficial effect is unclear, especially in CHF. Isosorbide dinitrate reduces pulmonary capillary wedge pressure (PCWP) after a first dose. The improvement in exercise capacity is not apparent in the short term but is evident after long-term nitrate administration. Nitrates do not affect hemodynamics at maximal exercise but do reduce PCWP during submaximal exercise in patients with CHF. This observation, in addition to increased oxygen extraction at peak exercise during nitrate administration, suggests a "training like" peripheral effect of nitrates in CHF. Lowering of PCWP by nitrates may be important, since vasodilators that do not reduce PCWP also do not improve exercise capacity in CHF. How PCWP influences exercise performance in CHF is unknown, but the mechanism may relate to effects of PCWP on pulmonary hemodynamics more than on ventilation and blood oxygenation.

Inhibition of platelet function by injectable isosorbide dinitrate

The possibility that isosorbide dinitrate (ISDN) inhibits platelet function in humans has been explored in vitro and in vivo. Incubation of citrated platelet-rich plasma from healthy subjects with scalar concentrations (1.25, 12.5 and 125 micrograms/ml) of ISDN for 5 and 10 minutes resulted in a decrease in platelet aggregation after ADP, adrenaline, and arachidonic acid at the highest drug concentration (mean decrease: 72% [p less than 0.01], 56% [p less than 0.05] and 62% [p less than 0.05], respectively, with the 10-minute incubation). Also, a significant reduction (30%) in generated thromboxane (TX)B2 levels was observed after arachidonic acid (p less than 0.01). ISDN was then infused at rate of 4 mg/hour for 30 minutes in 11 patients with angina and at a rate of 30 mg/hour for 20 minutes in 8. The smaller dose, which caused minor changes in arterial pressure and heart rate, was accompanied by a marked, significant decrease in ADP- and adrenaline-induced aggregation, with a nadir at 60 minutes from the infusion stop (decreases of 40% and 51% respectively). Circulating platelet aggregates also decreased, with a minimum (-41%, p less than 0.05) at the end of the infusion. The higher infusion rate, causing marked hemodynamic effects, was not accompanied by the occurrence of clear antiplatelet effects. Thus, ISDN can affect platelet function both in vitro and in vivo. The in vivo effect occurs at lower concentrations than in vitro but is blunted when a marked hemodynamic response occurs.

Cardiorespiratory effects of isosorbide dinitrate and nifedipine in combination with nadolol: a double-blind comparative study of beneficial and adverse antianginal drug interactions

Combinations of 2 or 3 drugs are often used to treat angina pectoris, but their combined cardiorespiratory effects have not been investigated. Using a randomized, double-blind, placebo-controlled protocol, the effects of nadolol alone and nadolol in combination with isosorbide dinitrate and nifedipine were compared, in low and high doses, on antianginal efficacy, respiratory functions and arterial blood oxygen saturation (SaO2) in 19 patients with stable angina pectoris. A complete assessment including a bicycle exercise test with the measurement of the sum of ST-segment depression in all leads (sigma ST) was carried out every 2 weeks. The frequency of anginal attacks and nitroglycerin consumption was reduced significantly (p less than 0.001) by nadolol alone and in combination with the other drugs. Nadolol caused a slight reduction in the forced expiratory volume in 1 second, which was improved by isosorbide dinitrate and nifedipine. The sigma ST profile (basal, at peak exercise and 2 and 5 minutes after exercise) was decreased by nadolol alone and in combination with the other drugs, although the greatest reduction was achieved with large doses of nifedipine and nadolol. The rest and postexercise SaO2 decreased after nadolol alone and in combination with isosorbide dinitrate, but recovered to pretrial values after nifedipine and nadolol. With all drug combination, sigma ST depression was greater when the postexercise SaO2 was less than 92%, and decreased (p less than 0.05) in the same patients when their postexercise SaO2 was greater than 92%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of sublingually administered nitroglycerin on regional myocardial blood flow in patients with coronary artery disease

The effect of sublingually administered nitroglycerin on regional myocardial specific blood flow (in ml/min per 100 g tissue) was evaluated with a xenon-133 washout technique in 31 patients in a resting nonstressed state. Eight patients had normal coronary arteriograms (Group 1), 12 had coronary artery disease without collateral vessels (Group 2) and 11 had coronary artery disease with collateral vessels (Group 3). Although nitroglycerin caused a similar decrease in mean arterial blood pressure and blood pressure-heart rate product in all three groups, the decrease in regional myocardial blood flow was significantly less in Group 3 (-8+/-6% [mean+/-standard error of the mean]) than in Group 1 (-31+/-5%), P less than 0.05); an intermediary decrease occurred in Group 2 (-23+/-5%). Within Group 3, there was a mean increase in regional myocardial blood flow after nitroglycerin in the five patients whose collateral vessels were of a higher angiographic grade and arose from non-stenosed coronary arteries, whereas a reduction was observed in the six patients with none or only one of these findings (+10+/-7% versus -23+/-3%, P less than 0.001). This study suggests that even in the resting state, in some patients with coronary artery disease enhancement of regional myocardial blood flow can occur after sublingual administration of nitroglycerin and is probably mediated through well functioning collateral vessels. It is possible that the drug's effects on both the coronary and systemic circulation may relieve angina in some patients with coronary artery disease.

Effect of sublingual nitroglycerin on cardiac performance in patients with coronary artery disease and non-dyskinetic left ventricular contraction

In 8 patients with coronary artery disease and symmetrical left ventricular contraction, an echocardiographic study of left ventricular function was performed before and 3 minutes after the administration of 0-6 mg nitroglycerin sublingually. The left ventricular end-diastolic diameter decreased from 5-2 +/- 0-2 to 4-9 +/- 0-2 cm (P less than 0-05) and the end-systolic diameter from 4-2 +/- 0-2 to 3-7 +/- 0-2 cm (P less than 0-001). The estimated stroke volume did not change significantly, while the cardiac output increased, 5-8 +/- 0-6 to 7-7 +/- 0-6 l min-1 (P less than 0-001) and the heart rate increased from 72 +/- 5 to 90 +/- 6 (P less than 0-001). The mean arterial blood pressure decreased from 105 +/- 4 to 88 +/- 3 mmHg (P less than 0-001). The ejection fraction increased from 53 +/- 3 per cent to 65 +/- 6 per cent (P less than 0-001) and the mean velocity of circumferential fibre shortening (VCF) from 0-81 +/- 0-05 to 1-15 +/- 0-10 circumferences per second (P less than 0-001). The estimated midsystolic midwall stress decreased from 155 +/- 14 g cm-2 to 102 +/- 12 g cm-2 after mitroglycerin (P less than 0-001). The administration of nitroglycerin was associated with a significant decrease in left ventricular preload and afterload. A vasodilating effect is suggested by the fall in peripheral resistance. The overall improvement in ejection fraction and VCF may not reflect a true increase contractility, because of the concomitant fall in wall stress.

Comparative hemodynamic effects of chewable isosorbide dinitrate and nitroglycerin in patients with congestive heart failure

Vasodilators are known to be effective in improving the hemodynamics of congestive heart failure by increasing cardiac output and reducing left ventricular filling pressure (LVFP). Long acting agents are needed to augment the practicality and availability of chronic vasodilator therapy. In the present study the vascular effects of chewable isosorbide dinitrate (CHIS), sublingual nitroglycerin (NTG) and placebo (P) were compared in eight patients with high LVFP due to heart failure. Patients with LVFP (pulmonary wedge pressure) over 14 mm Hg were given CHIS, 10 mg, NTG, 0.6 mg, and P, two chewable tablets, in random fashion. Heart rate (HR), blood pressure (BP) and LVFP were monitored for three hours after each drug. HR was not significantly affected by any drug, although it rose slightly after NTG and fell after CHIS. Significant reduction of BP occurred only after NTG, with peak effect at five minutes, but lasting only 15 minutes. NTG reduced LVFP 5.1 mm Hg (19.5%, P, less than 0.05), at peak effect, but LVFP was no longer significantly lower by 20 minutes after NTG. After CHIS, LVFP fell significantly within five minutes, reached a peak reduction of 8.6 mm Hg (32;7%, P less than 0.01) at 15 minutes, and remained significantly lower through three hours. Thus CHIS provides a nitrate action of rapid onset and sustained effect that may be useful for chronic vasodilator therapy of heart failure.