Left Ventricular Assist Device Insertion 

Updated: Jul 06, 2016
Author: Craig H Selzman, MD, FACS; Chief Editor: Karlheinz Peter, MD, PhD 

Overview

Background

Over the past several years, there has been a dramatic shift from the use of large pulsatile left ventricular assist devices (LVADs) to the use of smaller continuous-flow devices for the provision of mechanical circulatory support in patients with heart failure.[1] However, the fundamental issues related to surgical implantation remain the same. That is, most devices use the apex of the left ventricle (LV) as the inflow site to the pump, which subsequently gives off an outflow graft to the aorta, thus bypassing the ailing LV.

This article describes some of the issues related to implantation of LVADs. Although many types of devices are currently available, they do not differ significantly with regard to general implantation technique. Accordingly, this article focuses on the device currently dominant in the United States, the Thoratec HeartMate II. Other devices approved by the US Food and Drug Administration (FDA) include the Jarvik 2000 (Jarvik Heart, New York, NY) and the HeartWare Ventricular Assist System[2] (HeartWare, Framingham, MA).

Indications

Mechanical circulatory support can be used to salvage the cardiogenic shock patient and as a bridge to transplant therapy (BTT); it can also be permanent or be used for destination therapy (DT). In addition, patients who have durable LVADs implanted to determine their eligibility for transplant fall into a gray zone.

The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) follows all FDA-approved durable pump implants and has created a system for defining patient profiles. The algorithm for the patient with acute cardiogenic shock often involves insertion of nondurable pumps (INTERMACS Profile #1). This article remains focused on BTT, DT, and eligibility for transplant.

Most patients with LVADs are in progressive decline (INTERMACS Profile #2; inotrope-dependent with continuing deterioration) or are stable but inotrope-dependent (INTERMACS Profile #3). In addition, the INTERMACS Profile #4 group consists of patients with recurrent advanced heart failure (which is distinguished from refractory decompensation).

In general, most patients receiving durable LVADs have stage D and class IV heart failure. The evidence for routine use of LVADs to treat class III heart failure is still controversial. Most BTT patients have met institutional requirements for heart transplant. The authors use a similar workup for BTT and DT patients, including multidisciplinary assessment of comorbid conditions, behavior, and psychosocial characteristics.

Classic indications for DT versus BTT include, but are not limited to, the following:

  • Age
  • Diabetes
  • Pulmonary hypertension
  • Renal dysfunction
  • Recent malignancy

Contraindications

Although most patients listed for transplant are at some level candidates for mechanical circulatory support, there are several compelling factors that might argue for going straight to transplant, including multiple reoperations, congenital heart anomalies, restrictive heart disease with small ventricles, and other surgical issues (eg, previous pericardiectomy). These are all relative contraindications.

Extreme body mass indices (BMIs)—that is, being extremely underweight or extremely overweight—are also considered contraindications to LVAD implantation. Prior observational reports have suggested that morbidly obese patients have higher rates of driveline infections after LVADs. This was confirmed in a large study of the HeartMate II database; however, BMI did not influence short- and long-term survival.[3]

The most important contraindication for LVAD therapy is a right ventricle (RV) that is unable to support LVAD flows. Although it is not unusual (<10% of cases) to require temporary RV assist device (RVAD) support at the time of LVAD support, if one has a high suspicion of RV failure (based, for example, on severe dysfunction with a low right ventricular stroke work index and high right atrial pressures), the best options are biventricular assist devices, total artificial heart replacement, and transplant.

The emergence of DT has a created a different set of issues. Many DT patients are older and have end-organ dysfunction, and implants are seen as the last option or even a heroic measure. The ability of these patients to survive and thrive after LVAD must be seriously and rigorously evaluated by a multidisciplinary team.

Outcomes

Although the cumulative effect of advances in technology (with the smaller pumps) and overall improvements on the management of these patients has been positive, LVAD therapy is still associated with significant morbidity and mortality. The operative mortality for these patients ranges from 10-30%, with some preoperative assessments suggesting that it may be even higher.

According to a 2014 study that assessed 139 consecutive LVAD implantations as a bridge to transplantation at a single institution, both HeartMate II and the HeartWare Ventricular Assist System were associated with excellent early postoperative outcomes and good midterm survival.[4]

Ammirati et al, in Milan, assessed outcomes in older (>55 years) patients with advanced heart failure who were treated either (a) with a continuous-flow LVAD (CF-LVAD) with a BTT or bridge-to-candidacy (BTC) indication or (b) with heart transplant.[5]  Early and midterm outcomes were better for CF-LVAD with BTT indication than for heart transplant in these patients. At 2-year follow-up, outcomes were similar for CF-LVAD with BTT or BTC indications and for heart transplant. The authors noted that these results require confirmation in larger, more varied populations and with longer follow-up periods.

 

Periprocedural Care

Preprocedural Planning

As a general note, the success of a left ventricular assist device (LVAD) implantation procedure depends on more than just technique. Judicious preoperative evaluation and preparation must be combined with vigilant postoperative management of both the usual issues encountered in the intensive care unit (ICU) and the issues arising in the outpatient setting. This can be accomplished only through the efforts of an active and engaged multidisciplinary team.

Issues that must be taken into account in planning the care of an LVAD patient include cardiovascular disease and anticoagulation.

Coronary artery disease (CAD) in LVAD patients is usually related to the right ventricle (RV). In a right-dominant system with significant disease in the right coronary artery, a bypass graft to that artery is advisable. To the extent possible, protect all patent grafts at the time of reentry.

General guidelines for valve disease are as follows[6] :

  • Aortic stenosis - This is generally not a problem and can be left alone
  • Aortic insufficiency - This must be fixed if it is more than mild; options include bioprosthetic aortic valve replacement (AVR), oversewing the valve with a collagen-impregnated Dacron patch (eg, Hemashield; Maquet, Rastatt, Germany), and approximation of the nodes of Arantius; the authors prefer not to oversew the valve, because oversewing makes the patient completely dependent on the LVAD for left ventricular (LV) ejection
  • Prosthetic AVR - A bioprosthetic AVR is not a problem, but there are as yet no data suggesting what to do with a mechanical AVR; some surgeons recommend oversewing or replacement with a bioprosthetic AVR (especially in destination therapy [DT] patients), whereas others might consider leaving the prosthesis in place; this scenario was an exclusion criteria for patients in current trials
  • Mitral stenosis - This must be repaired to allow LV inflow; options include tissue valve replacement and, if the situation is amenable, valvuloplasty
  • Mitral regurgitation - This can be left alone unless myocardial recovery and explantation are being considered
  • Tricuspid regurgitation - Although the practice is controversial, most perform annuloplasty or replacement in the face of severe tricuspid regurgitation [7]

The authors usually administer warfarin when the patient is extubated and taking oral medications, the ultimate goal being an international normalized ratio (INR) of 1.7-2.5. If the time before initiation of warfarin is extended, the authors administer heparin.

Other circumstances can also alter surgical strategies and must therefore be taken into account in planning, including previous cardiac surgical procedures (eg, congenital repairs or ventricular restoration).[8, 9, 10]

Equipment

No particular specialized equipment is necessary for insertion of an LVAD. Each device usually comes with its own specific tools for implantation; these tools can rarely be used on competing devices. Most centers that implant durable LVADs also have the capacity to implant either short-term or durable RV assist devices (RVADs) if necessary.

This article focuses on insertion of the Thoratec HeartMate II (see the image below), which is the dominant LVAD in the United States at present. Other devices approved by the US Food and Drug Administration (FDA) include the Jarvik 2000 (Jarvik Heart, New York, NY) and the HeartWare Ventricular Assist System[2]  (HeartWare, Framingham, MA).

HeartMate II (Thoratec, Pleasanton, CA). HeartMate II (Thoratec, Pleasanton, CA).

Patient Preparation

Anesthesia

Standard cardiac surgery anesthesia is used with LVAD procedures. Double-lumen tubes or bronchial blockers can be used for off-pump procedures that necessitate left thoracotomy. Typical monitoring equipment routinely used includes temperature probes, pulmonary artery catheters, and cerebral oximetry.

Although most procedures are done with the use of cardiopulmonary bypass, many centers maintain low tidal volume ventilation during bypass on the grounds that this should theoretically decrease postpump pulmonary vascular resistance. Antifibrinolytic therapy is usually employed, and blood products are given as indicated. Some centers rely heavily on thrombelastography for driving replacement therapy.

Most LVAD procedures can be performed without systemic cooling, and routine measures for cardiopulmonary bypass are used. The authors frequently employ ultrafiltration and avoid excessive hemodilution. Intraoperative cell salvage should be replaced with concomitant liberal use of fresh frozen plasma (2-3:1). In patients with heparin-induced thrombocytopenia, LVAD implantation has been performed successfully, albeit with additional risk, by using alternative anticoagulants such as bivalirudin or argatroban.

After insertion of the LVAD, attention is focused on decreasing pulmonary vascular resistance and protecting RV function. Some centers routinely use nitric oxide in each case. Every effort is made to reduce transfusion requirements as well as avoid hypoxia, hypercarbia, and acidosis. Intravenous pulmonary vasodilators, including nitrates and phosphodiesterase inhibitors (milrinone), are routinely used.

Inotropic support for the RV is also routinely provided (eg, with milrinone, epinephrine, and dobutamine). The use of sildenafil in these patients is increasingly noted, both preoperatively and perioperatively. Patients with sick RVs may require mechanical support for several days (eg, with a centrifugal blood pump such as the CentriMag [Thoratec, Pleasanton, CA]).

Positioning

Most LVADs are placed with the patient in the supine position, as is standard for any cardiac surgery operation. This standard position can be used for several nonsternotomy approaches as well. For example, some surgeons have placed pumps (notably the Jarvik 2000) through a left subcostal incision, with the outflow to the supraceliac aorta. Others have used a left subcostal incision for the HeartMate II and tunneled the outflow graft to the ascending aorta through a counterincision in the right third interspace.

A left thoracotomy approach can also be used, with the outflow graft to the descending aorta. This technique has been most often applied to the off-cardiopulmonary bypass approach using the Jarvik 2000 LVAD, but in theory it could be used for several other small pumps as well.[11] In such cases, the patient should be placed in the left lateral position, with the hips turned back to give access to the left femoral vessels if needed.

 

Technique

Approach Considerations

Although individual surgeons and centers employ different methods to insert a left ventricular assist device (LVAD), the fundamental concepts remain true for all. That is, most devices use the apex of the left ventricle (LV) as the inflow site to the pump, which subsequently gives off an outflow graft to the aorta, thus bypassing the ailing LV. Currently available devices do not differ significantly with regard to general implantation technique. The sequence of implantation can vary also from patient to patient, depending on the particular situation. In some cases, concomitant procedures may be performed in conjunction with LVAD implantation without adversely affecting outcome.[12]

Insertion of LVAD

After induction of anesthesia, placement of monitoring lines, and patient positioning, a median sternotomy is performed. In many cases, this is a redo sternotomy. If the patient has a hostile mediastinum (eg, from multiple or recent surgical procedures, congenital heart disease, enlargement of the right ventricle [RV], or substernal grafts), alternative forms of cannulation for cardiopulmonary bypass should be considered.

Arterial inflow can be accessed through the subclavian or femoral arteries. The authors usually sew a side-armed graft on the vessel. Venous return is through a long femoral arterial cannula placed under the guidance of transesophageal echocardiography (TEE) with the tip in the superior vena cava (SVC).

Before full heparinization and sternal reentry, many surgeons try to develop the LVAD pocket. Full creation of the pocket is made easier when the sternum is open. There are two schools of thought regarding pocket location: one prefers the pocket to be within the preperitoneal space, whereas the other prefers it to be between the posterior rectus sheath and the rectus abdominis.

For the larger pumps, the latter location was routinely chosen so as to avoid peritoneal erosion. However, for the smaller pumps, which require smaller pockets, many surgeons have gone back to the preperitoneal approach just over the diaphragm. Most surgeons take down the anterior slip of diaphragm laterally to allow the inflow cannula to orient correctly. Either an electrocautery or a vascular endoscopic stapler can be used to divide this muscle. It is important to check this transection line before closure; it often has points of bleeding.

Most devices come with a manufactured model to allow accurate sizing. To assist with sizing, the pericardium is opened and the LV apex identified. One of the useful features of the HeartMate II device is its inflow elbow, which theoretically allows good placement without the need to develop the pocket as far laterally.

The prospective site for driveline exit is then identified. It is usually in the typical right upper quadrant position but may vary according to the patient’s need. A tunneling device is brought through the right rectus sheath. Sufficient subfascial dissection should be performed on the right side to allow tension-free closure as well as provide space for driveline exit. At this point, the authors typically go into the left pleural space and place a 28-French soft Silastic tube in this cavity; once the LVAD is in place, getting back into this space is more difficult.

On the back table, the pump is prepared according to the manufacturer’s instructions. Some outflow grafts require preparation. Some devices require reinforcement, whereas others are ready to go when taken out of the package. Individual pump preparation is beyond the scope of this article, especially in view of the excellent training provided by all of the device manufacturers with regard to their respective pumps.

After heparinization and before significant manipulation of the heart, the authors place cannulation sutures in the ascending aorta and the right atrial appendage. The latter suture can then be retracted inferiorly to expose the touchdown spot on the proximal lateral ascending aorta. The HeartMate II outflow, as opposed to the HeartMate I outflow, does not easily pass out into the right chest. Consequently, a more anterior aortotomy may be required, with the graft passing over the anterior atrioventricular groove or over the RV.

With the model in place, the outflow graft is stretched and cut to size with a slight bevel. The authors place a bulldog clamp on the bend relief to keep it out of the way. After the touchdown spot is marked with a marking pen, a side-biting aortic cross-clamp is placed. An aortotomy is created with a No. 11 scalpel and opened with Potts scissors. The two ends are rounded with a 4.5-mm proximal coronary punch.

The distal anastomosis may be sewn with any of a number of techniques. Some surgeons place individual pledgeted mattress or continuous sutures over felt or pericardium. The authors typically place 4-0 polypropylene sutures at the heel and toe and run them down each side toward each other. After removal of the cross-clamp, hemostasis is checked, and repair sutures are placed as necessary.

Aortic and right atrial cannulas are placed; the authors often place an aortic vent needle as well. The patient is placed on cardiopulmonary bypass and maintained at normothermia. As mentioned above, even via a median sternotomy, this procedure can be performed without the use of cardiopulmonary bypass. That said, most centers do perform the remainder of the operation with the patient on bypass.

The heart is elevated with the assistance of laparotomy packs in the posterior mediastinum. The left anterior descending artery is identified, thus marking the intraventricular grove. A silk suture is placed in the epicardium of the site of the core; the suture is brought through the coring knife.

With larger ventricles, identification of the apex is fairly straightforward. With smaller ventricles, some surgeons core a little further anteriorly to provide a reasonable angle. The core is excised. The LV cavity is inspected, and further debridement of trabeculae or thrombus is performed as necessary. The alignment along the interventricular septum is also examined.

Large full-thickness pledgeted sutures (the authors use polyester; others use polypropylene) are then passed. The sutures are placed in a mattress fashion to catch the edge of the epicardium. Most surgeons use 12-14 sutures, though some use fewer. The sutures are attached to the sewing ring and tied. The authors often put a very thin layer of surgical adhesive (eg, BioGlue; CryoLife, Atlanta, GA) over the insertion site and pledgets.

The prospective driveline site is cored, and the tunneling device is passed subcutaneously and through the rectus at the inferior right margin of the incision. The controller and pump are brought to the table. The driveline is passed and connected to the controller. During this time, the authors insufflate carbon dioxide into the LV cavity to evacuate air.

The inflow stabilizing ring is removed. The LV cavity is inspected to make sure that the inflow is clear. The inflow cannula is inserted and secured with the sewing rings suture. The authors use two tie bands to secure the cannula further; others place several large suture ties.

At this point, the anesthesiologist and perfusionists have been given ample time for weaning. Inotropic support is provided, full ventilation ensues, calcium is repleted, and acid-base status is corrected. Some routinely use nitric oxide to assist with reduction of pulmonary vascular resistance.

A separate 4-0 pledgeted polypropylene suture is placed just above the outflow clamp for deairing. The aortic graft is backbled. Volume is left in the heart, and the outflow cap is loosened to help deair the ventricle. The outflow graft is then connected. The bend relief should not be latched until the outflow graft clearly does not kink when being attached to the pump. The patient is weaned off cardiopulmonary bypass or to a flow rate of 1-2 L/min.

The LVAD is started at the lowest setting for revolutions per minute (RPM), with the aortic clamp on to continue deairing. With the aortic vent on, the outflow graft clamp is removed. Often, a small rush of air bubbles is visible on the long-axis TEE view, reflecting air around the clamp. Usually, this rush lasts for less than 5 seconds, and the air is removed with the aortic vent.

LVAD flow is slowly increased while right-side function, pressures, and septal motion are monitored. Often, no flow is recorded, but the patient is still doing well. The temptation to increase RPM quickly so as to get high flow should be resisted. In most centers, it is permissible to leave the operating room without full decompression as long as the patient’s hemodynamic status is suitable. Often, “final” settings on the pump are not made for days after the implant. Protamine is administered and all cannulas removed. Chest and mediastinal tubes are placed.

The final position of the LVAD within the chest, especially without the retractor, should be viewed under TEE. In particular, the inflow cannula should be directed slightly posteriorly toward the mitral valve; TEE is crucial for this step. In addition to confirming cannula location, TEE can identify valvular problems.

A bubble study must be performed with the LVAD on in order to determine whether a patent foramen ovale (PFO) is present. In patients who have heart failure and high left-side pressures, such defects can be difficult to detect until the left side is decompressed. If a PFO is identified, it must be repaired.

Some centers advocate an aggressive policy of leaving the chest open for 1 day to allow stabilization before closure. The authors’ approach is to leave the chest open if there are grounds for concern regarding ongoing bleeding or RV functional decline associated with sternal compression. Leaving the sternum open can be an excellent strategy for marginal patients. In this situation, the authors usually wrap a towel in an antimicrobial incise drape (eg, Ioban; 3M, St Paul, MN) and place it in the cavity, with a large drape covering it and the chest.

For bridge to transplant therapy (BTT), the authors prefer to prepare for reentry that occurs with transplant. Initially, the authors try to space the aortic cannulation site and the outflow graft so as to leave space for recannulation, an aortic cross-clamp, and a cuff of sewable aorta. Some surgeons place vessel loops around the SVC and the inferior vena cava (IVC) to facilitate identification. The authors have done this with some reoperative LVAD cases; however, if possible, they try not to create dissection planes unless it is necessary.

The authors take a piece of spare graft to cover the outflow graft from the edge of the bend relief to the aorta. They then place a piece of 1-mm Gore-Tex (W. L. Gore & Associates, Newark, DE) at the base of the pericardium on the left side, where it joins the diaphragm, and use interrupted sutures to reconstruct the pericardium and isolate the LVAD. It is important to try to separate the left lung from the device; this can be quite traumatic at the time of explant. Other barrier products can also be used to help with transplant reentry.

There are several ways of dealing with the driveline. In general, a long tunnel is desirable. The authors have stopped bringing the velour cuff out of the incision; they believe that healing has actually been better without the cuff. The authors place a deep 0 polyglactin suture and use a 3-0 poliglecaprone suture for the subcuticular skin closure. In addition, they authors use two No. 1 polypropylene sutures to provide traction relief around the exit line. These later sutures are removed about 1 month after being placed.

Complications

Well-known complications include the following:

  • Bleeding that necessitates reoperation or transfusion
  • Neurologic events (including stroke, both ischemic and hemorrhagic)
  • Infections (both LVAD-related and remote)
  • Arrhythmia
  • Respiratory failure
  • Renal failure
  • Hepatic dysfunction
  • Hemolysis [13]
  • Pump thrombosis [14, 15]
  • Rehospitalization

Certain intraoperative complications associated with LVAD implantation are of particular importance. The foremost of these is RV failure.[16] The authors take an aggressive approach to temporary RVAD support. Rather than leave the patient in the operating suite on high doses of multiple inotropes and vasoconstrictors, the authors are inclined to place a temporary RVAD to allow hemodynamic and coagulopathic stabilization. This pump can usually be removed within 5 days.

Another potentially catastrophic intraoperative complication is related to air embolism. Although some air is to be expected, especially as pumping is initiated, persistent air entrainment should lead to suspicion of apical disruption of the inflow cannula.

 

Medication

Medication Summary

Standard cardiac surgery anesthesia is used with LVAD procedures. The goals of pharmacotherapy are to reduce morbidity and prevent complications.

Anesthetic Agents

Class Summary

After standard monitoring equipment is attached and peripheral venous access achieved but before the arterial line is inserted, the midazolam dose is administered. Before placement of the arterial line, it should be ensured that a radial artery graft will not be used for CABG.

Propofol (Diprivan)

Propofol is a phenolic compound unrelated to other types of anticonvulsants. It has general anesthetic properties when administered intravenously. Propofol IV produces rapid hypnosis, usually within 40 seconds. The effects are reversed within 30 minutes following the discontinuation of infusion. Propofol has also been shown to have anticonvulsant properties.

Etomidate (Amidate)

Amidate is a nonbarbiturate imidazole compound with sedative properties. It is short acting and has a rapid onset of action; the duration of action is dose dependent (15-30 minutes). Its most useful feature as an induction agent is that it produces deep sedation while causing minimal cardiovascular effects.

The major application of etomidate is induction for endotracheal intubation, particularly in patients with, or at risk for, hemodynamic compromise. Etomidate has been shown to depress adrenal cortical function; however, this effect is not significant clinically during short-term administration. Since the drug is mixed in propylene glycol, continuous infusion not recommended.

Thiopental

Thiopental is a short-acting barbiturate sedative-hypnotic with rapid onset and a duration of action of 5-20 minutes. Like methohexital, it is most commonly used as an induction agent for intubation. To use thiopental as a sedative, titrate in dosage increments of 25 mg (adjust to lower dose in children).

Isoflurane (Forane, Terrell)

Isoflurane is an inhalation anesthetic. It may have a myocardial protective effect and therefore is especially useful in off-pump surgery. Isoflurane potentiates the effects of muscle relaxants. Small doses of muscle relaxants can achieve complete paralysis when administered concomitantly with isoflurane.

Antifibrinolytic Agents

Class Summary

Antifibrinolytics are used to enhance hemostasis when fibrinolysis contributes to bleeding. Because of the risk of thromboembolic events, screening for pulmonary AVMs should be performed before use.

Aminocaproic acid (Amicar)

Aminocaproic acid inhibits fibrinolysis via inhibition of plasminogen activator substances and, to a lesser degree, through antiplasmin activity.

Tranexamic acid (Cyklokapron, Lysteda)

Tranexamic acid is an alternative to aminocaproic acid. It inhibits fibrinolysis by displacing plasminogen from fibrin.

Blood Components

Class Summary

Plasma is the fluid compartment of blood containing the soluble clotting factors.

Fresh frozen plasma

Fresh frozen plasma is for use in patients with blood-product deficiencies.

Anticoagulants, Hematologic

Class Summary

Anticoagulants prevent recurrent or ongoing thromboembolic occlusion of the vertebrobasilar circulation. In patients with heparin-induced thrombocytopenia, LVAD implantation has been performed successfully, albeit with additional risk, by using alternative anticoagulants.

Heparin

Heparin may be used if thrombocytopenia is not present. Heparin augments the activity of antithrombin III and prevents conversion of fibrinogen to fibrin. It does not actively lyse but is able to inhibit further thrombogenesis. Heparin prevents the recurrence of a clot after spontaneous fibrinolysis.

Argatroban

Argatroban is a selective thrombin inhibitor that inhibits thrombin formation by binding to the active thrombin site of free and fibrin-bound thrombin. It inhibits thrombin-induced platelet aggregation.

Dabigatran etexilate (Pradaxa)

Dabigatran etexilate is a selective thrombin inhibitor that inhibits thrombin formation by binding to the active thrombin site of free and fibrin-bound thrombin. It inhibits thrombin-induced platelet aggregation.

Bivalirudin (Angiomax)

Bivalirudin inhibits coagulant effects by preventing thrombin-mediated cleavage of fibrinogen to fibrin.

Pulmonary Vasodilators

Class Summary

After insertion of the LVAD, attention is focused on decreasing pulmonary vascular resistance and protecting RV function. Inhaled nitric oxide (NO) is a pulmonary vasodilator indicated to treat pulmonary hypertension. NO is also being studied for severe hypoxemia in acute respiratory distress syndrome (ARDS).

Nitric oxide, inhaled (INOmax)

NO is produced endogenously from the action of the enzyme NO synthetase on arginine. It relaxes vascular smooth muscle by binding to the heme moiety of cytosolic guanylate cyclase, activating guanylate cyclase, and increasing intracellular levels of cyclic guanosine monophosphate (cGMP), which then leads to vasodilation. When inhaled, NO decreases pulmonary vascular resistance and improves lung blood flow.

Vasodilators

Class Summary

Nitrates reduce myocardial oxygen demand by lowering preload and afterload. In severely hypertensive patients, nitroprusside causes more arterial dilatation than nitroglycerin. Nevertheless, in view of the possibility of thiocyanate toxicity and the coronary steal phenomenon associated with nitroprusside, IV nitroglycerin may be the initial therapy of choice for afterload reduction.

Nitroglycerin sublingual (Nitro-Bid, NitroMist, Nitrostat, Nitrolingual)

Sublingual nitroglycerin tablets and spray are particularly useful in patients who present with acute pulmonary edema with a systolic blood pressure of at least 100 mm Hg. As with sublingual nitroglycerin tablets, the onset of action of nitroglycerin spray is 1-3 minutes, with a half-life of 5 minutes. Administration of the spray may be easier, and it can be stored for as long as 4 years.

Topical nitrate therapy is reasonable in a patient presenting with class I-II congestive heart failure (CHF).

Nitroprusside sodium (Nitropress)

Nitroprusside produces vasodilation of venous and arterial circulation. At higher dosages, it may exacerbate myocardial ischemia by increasing the heart rate. It is easily titratable.

Inotropic Agents

Class Summary

Inotropic support for the RV is routinely provided (eg, with milrinone, epinephrine, and dobutamine).

Milrinone

Milrinone is a bi-pyridine–positive inotrope and vasodilator with little chronotropic activity.

Dopamine

Dopamine is a naturally occurring endogenous catecholamine that stimulates beta1-and alpha1-adrenergic and dopaminergic receptors in a dose-dependent fashion. It stimulates the release of norepinephrine.

In low doses (2-5 μg/kg/min), dopamine acts on dopaminergic receptors in renal and splanchnic vascular beds, causing vasodilatation in these beds. In midrange doses (5-15 μg/kg/min), it acts on beta-adrenergic receptors to increase heart rate and contractility. In high doses (15-20 μg/kg/min), it acts on alpha-adrenergic receptors to increase systemic vascular resistance and raise blood pressure.

Dobutamine

Dobutamine is a sympathomimetic amine with stronger beta than alpha effects. It produces systemic vasodilation and increases the inotropic state.

Epinephrine (Adrenalin)

Its alpha-agonist effects include increased peripheral vascular resistance, reversed peripheral vasodilatation, systemic hypotension, and vascular permeability. Its beta2-agonist effects include bronchodilation, chronotropic cardiac activity, and positive inotropic effects.