Interventional Techniques for Device Implantation

The first generation of cardiac implantable electronic devices (CIEDs) were implanted by surgeons, initially with epicardial and later transvenous pacing systems. Because of this, when problems were encountered the solution was a surgical technique. As devices became smaller and almost exclusively implanted using transvenous techniques, implantation moved largely out of the hands of the surgeon and to the invasive cardiologists and electrophysiologists (EP). The mechanics of de novo, transvenous device implantation are generally straightforward and well suited for a cardiologist's skill set. With the advent of cardiac resynchronization therapy (CRT), the complexity of device implantation has increased greatly. Navigating the tortuous anatomy of the tributary branches of the coronary sinus (CS) is more akin to an interventional coronary arterial procedure than a standard pacemaker lead implantation. Relying on “old” techniques for placement of left ventricular leads results in a failure rate between 7.5% and 9% even in experienced hands. As a result, EP physicians have had to learn entirely new skills and equipment. This chapter will address the skills and equipment that are essential for very high rates of successful left ventricular (LV) lead placement.

Interventional Versus Electrophysiologic Approach

How would an interventional cardiologist approach the difficult scenarios sometimes encountered during LV lead placement? Interventional cardiologists are well acquainted with the use of specialty catheters, wires, balloons, snares, and other tools that are less familiar to even the experienced electrophysiologist.

Consider the situation of adding a new pacing or defibrillation lead to a system in the presence of an occluded subclavian vein. With expanded indications for implantable cardioverter-defibrillators (ICDs) and CRT, as well as the increased survival of patients with cardiovascular disease, the prevalence of subclavian vein obstruction or occlusion in patients with preexisting leads can be as high as 45%. An implanter familiar with interventional techniques might attempt crossing of the occlusion followed by balloon dilation (venoplasty) of the stenosis before considering more invasive procedures such as tunneling or surgical lead placement.

Left ventricular lead placement for CRT requires the successful completion of multiple steps, many originating in the interventional arena. Intubation of the CS ostium, identification of a target vein with contrast injection, manipulation of a wire into a CS branch and advancement of a pacing lead into a small and often tortuous segment are steps similar to what an interventional cardiologist encounters during percutaneous coronary intervention (PCI). Lacking specific training in this realm, the traditional EP skill set (which is reliant upon wires for CS access and lead advancement) is less well-suited to LV lead placement. With adoption of new tools and training in interventional techniques, implanting physicians who transitioned from a standard over-the-wire implant technique to a contrast and catheter-based lead delivery system have experienced significantly fewer LV lead failures, more optimal lead positioning, and shorter case times. Even in the case of extremely unfavorable anatomy, implant success is improved with the adoption of interventional techniques. A few learned skills can have a significant impact on procedural and patient outcomes ( Box 32-1 ).

Box 32-1

Interventional “Toolbox” for Device Implantation

Subclavian Vein Stenosis/Occlusion

Establish access across occlusion (wire manipulation, lead sacrifice, laser tunneling)
Balloon venoplasty

Left Ventricular (LV) Lead Delivery

Preshaped catheters for coronary sinus (CS) access, target branch access and lead delivery
Contrast injections to identify vascular structures
Lead advancement based on guide-support not wire support

Tortuous or Stenotic Coronary Sinus Branch

Anchoring balloons
Coronary sinus venoplasty
Snare technique

Failed LV Lead Placement

Transseptal (endocardial) LV lead placement

Failed Defibrillation Threshold (DFT) Testing

Placement of azygos coil

Morbidity and Mortality

Although there are no randomized trial data comparing outcomes between transvenous and epicardial LV lead placement, case series and registries show an increase in adverse events with surgical lead placement. In a series of 452 patients, 10% of whom had failed transvenous LV lead insertion and went on to epicardial lead placement, acute renal injury and infection were significantly higher compared with matched-controls (26.2% vs. 4.9%: P = 0.0004; and 11.9% vs. 2.4%; P = 0.03, respectively). The REPLACE study examined outcomes in patients undergoing device replacement (pacemaker or defibrillator), including 407 patients with planned upgrade to CRT. In this registry, there were four deaths among the 48 patients who required an epicardial lead following a failed transvenous approach (8% mortality). Other studies, however, have shown no difference in acute or long-term mortality when comparing surgical LV lead placement to matched controls undergoing standard transvenous lead insertion, although length of hospital stay is significantly increased in the surgical cohort. Some patients with a failed attempt at transvenous LV lead placement refuse surgery or are deemed too high-risk for epicardial lead placement. Failure to place a CRT device in an otherwise appropriate patient would deny them a proven, life-saving therapy.

Device Implantation–Specific Interventional Skill Set

A skill set is defined as the combination of knowledge base and technical skills. Because the terms, tools, and techniques used in the interventional approach to device implantation may be unfamiliar, a glossary box is provided for reference.

Glossary and Definition of Terms

LV lead delivery system is defined as the set of catheters used to place an LV lead in a coronary vein. A delivery system consisting of three telescoping components: (1) the coronary sinus (CS) access catheter; (2) the delivery guide; and (3) the vein selector increases the success and efficiency of the implant procedure.
Coronary sinus (CS) access catheter is defined as a removable catheter designed to cannulate the CS and provide access and support for delivery of a left ventricular (LV) lead to the target vein. The lumen size of most device company CS access catheters is 7 French (7 Fr), while larger catheters up to 9 Fr (SafeSheath CSG Worley, Pressure Products, San Pedro, CA) are available and may expand LV lead implant options. Delivery guides are intended to be advanced through a CS access catheter.
Delivery guide is defined as a sliceable catheter designed to fit into the target vein and provide direction and support for advancing the LV lead. Proper use of a delivery guide eliminates the reliance on wire support for lead advancement. Delivery guides are not intended for CS cannulation. The shape and size of a delivery catheter, while suited for lead delivery, may not be optimal for target branch access. Localization and wire advancement into the target branch is best achieved with the assistance of a vein selector.

Vein selector is defined as a small (5 Fr), soft-tip catheter that telescopes inside a delivery guide to extend beyond the delivery guide and locate the target vein using puffs of contrast, provide direction and support for advancing wire(s) into the vein, then serve as a rail over which to advance the delivery guide. While not large enough for lead delivery, the angulation of a vein selector (90, 110, or 130 degrees) and softness of the tip allows easier access to the target vessel than using a delivery catheter alone.
Extra-support wires. Advancing a balloon, catheter, or sheath over a stiffer wire may be necessary to prevent buckling. The 0.035-inch Amplatz Extra Stiff (Cook Medical, Bloomington, IN) is suitable in many cases, but on occasion the 0.035-inch Amplatz Ultra Stiff is required. The Amplatz wires are also available in 0.032-inch size, which may be required for some sheaths. The Amplatz wires are stiff and do not advance easily through tortuous or narrow venous structures; thus, they are inserted via an exchange procedure using a small catheter.
Exchanging of wires to augment support. When a more supportive wire is required to advance the guide/sheath, a small catheter (4 Fr-5 Fr) is advanced over the existing wire into the pulmonary artery or inferior vena cava, the existing wire removed, the Amplatz inserted, and the exchange catheter removed. A hydrophilic 4-Fr to 5-Fr catheter will advance where a catheter with a standard surface will not, so it is important to have hydrophilic catheters on hand for exchange. To avoid the need for exchange-length wires, the catheter should be 60 to 70 cm in length. (e.g., Quick-Cross 0.035-inch 65-cm Support Catheter, Spectranetics, Colorado Springs, CO).
Venoplasty. After advancement of a wire across a subclavian vein occlusion and wire exchange to augment support, a 6- to 9-mm diameter peripheral balloon is inflated to open the stenosis sufficiently to allow the sheath(s) to advance without resistance. Temporary (rather than permanent) vein patency is the goal and vessel stenting is not required nor advised due to entrapment of the existing leads. Venoplasty of CS branch vessels can also be performed with small diameter, coronary balloons.
Focused-force venoplasty. The addition of a stiff wire beside the inflated balloon focuses the force of the balloon against the occlusion. Focused force is used for both focal and diffuse occlusions.
Hydrophilic wires/catheters and balloons. Materials that are intrinsically hydrophilic or have a hydrophilic coating are slippery to the touch when wet and offer much less resistance to passage through vascular structures than standard materials of the same size and configuration. Their disadvantage is that hydrophilic wires/catheters can be difficult to handle and direct.
“Push-pull” technique is used to advance the tip of a delivery guide into the ostium of the target vein. With the tail of the balloon at the tip of the guide, advance the guide (push), holding traction on the balloon as it is deflated (pull).

Knowledge Base

The knowledge base includes familiarity with the equipment required for the procedure, the proper preparation and use of contrast, comfort with open-lumen catheter manipulation and wire exchange, proper selection of preshaped guiding catheters used to cannulate specific venous structures, and familiarity with the preparation and use of additional interventional tools (balloons, snares, etc.). At various points of the procedure, where both catheter manipulation and visualization of the target vessel are paramount, it is important to have an assistant familiar with contrast injection, thereby allowing the operator to keep both hands on the catheter. Interventional implanters should know which tools to use for crossing a venous obstruction, the type and size of balloons to use for which veins, how to prevent hemothorax during subclavian venoplasty, which implant problems respond to the balloon anchoring technique and which to the snare technique, and how sacrificing a lead, using a wire under the insulation or laser extraction can be used to regain venous access.

Technical Skills

Technical skills in an interventional skill set include torque control using both hands on the catheter, catheter manipulation while contrast is injected by the assistant, vein-specific catheter techniques (specific preshaped catheter used a specific way for a specific vein), and techniques to gain, optimize, and maintain guide support. Implanters must know techniques for crossing venous obstruction associated with device leads (wire manipulation and venoplasty of stenotic veins), as well as venoplasty of stenotic or occluded CS branch vessels in patients with and without prior open-heart surgery. Finally, implanters need to be familiar with the mechanical operation of snares as well as the “push-pull” technique used with anchoring balloons.

Training

For many new surgeries or invasive procedures, a trainee's proficiency is dependent on chance opportunities during residency or fellowship. Alternatively, a simulator-based training program in which the environment can be altered to model the experiences encountered and to generate feedback about both technical skills and knowledge base may provide both a broader and more comprehensive training experience. As experience grows, physicians who have adopted the interventional approach, together with device manufacturers and professional societies, can create programs to help the traditional EP physician develop the knowledge base and skill set specific to device implantation.

Use of Contrast Material

Essential to nearly every aspect of interventional device implantation is the use of contrast to visualize vascular structures to successfully guide catheter, wire, or balloon placement and better inform treatment options. When considering the use of contrast for LV lead placement, keep in mind that a successful implant not only improves symptoms, but also reduces morbidity and mortality. Failure to implant an LV lead or suboptimal placement of the lead due to inadequate visualization of a target vessel may significantly impact patient outcomes. Therefore, the following points should be considered:

1.
Contrast is essential to successful application of interventional device techniques.
2.
The safety of contrast is patient-specific and modifiable.
3.
Safe use of contrast requires advanced patient preparation.
4.
Most patients with a history of heart failure can be hydrated safely.
5.
Renal failure is more difficult to treat than volume overload.

Prevention of Contrast-Induced Nephropathy

Renal insufficiency is present in more than half of patients with heart failure. Although uncommon in most situations, contrast-induced nephropathy (CIN) can be an important complication of CRT associated with increased morbidity and mortality and extended hospital stay. Patients with congestive heart failure and preexisting renal insufficiency are at increased risk for CIN but ultimately CRT improves renal function by improving cardiac function. A metaanalysis of 18 studies of CRT in patients with renal dysfunction found that CRT is associated with modest improvements in estimated glomerular filtration rate (eGFR) (mean difference 2.30 mL/min per 1.73 m ² ; 95% confidence interval, 0.33 to 4.27) and significant improvement in left ventricular ejection fraction (LVEF) (mean difference 6.24%; 95% confidence interval, 3.46 to 9.07).

Recognizing the importance of contrast administration to a successful procedure, in most situations it is more important to focus on mitigating the risk of contrast rather than minimizing or eliminating its use. Despite efforts to limit its use, the volume of contrast frequently exceeds expectation. Further, the nephrotoxicity of even a small volume of contrast (10-30 mL) in the unprepared patient can be significant, whereas the risk of CIN can be reduced if preventive steps are taken before the implant.

After exposure to contrast, the kidneys concentrate contrast material in the urinary space within the renal tubules, releasing nitric oxide from endothelial cells and triggering a transient vasodilation. This is followed by prolonged vasoconstriction causing tubular cell damage, extravasation into the peritubular space and constriction of the latticelike peritubular blood vessels in the outer medulla. Sustained vasoconstriction can last for hours to days, resulting in ischemic injury to the outer medulla, particularly in those with chronic kidney disease and diabetes mellitus ( Box 32-2 ).

Box 32-2

Risk Factors for Contrast-Induced Nephropathy

Patient Related

Chronic kidney disease
Diabetes mellitus
Age
Urgent/elective procedure
Anemia
Hypotension
Hypertension
Congestive heart failure
LVEF *

* Left ventricular ejection fraction.

<40%
Intraaortic balloon pump

Nonpatient Related

Contrast with high osmolality
Contrast volume

Contrast-induced nephropathy is typically defined as a 25% or greater increase in baseline serum creatinine, or a 0.5-mg/dL increase without another identifiable cause. CIN occurs 24 to 48 hours after exposure, with serum creatinine peaking at 3 to 5 days, returning to normal within 2 weeks, although usually by 7 to 10 days. The approach to the prevention includes (1) hydration to dilute and flush contrast from the kidney, (2) selection of less nephrotoxic contrast agent, (3) drugs to protect the kidney and prevent vasoconstriction, and (4) hemofiltration or hemodialysis.

A bedside risk score stratifies patients into low (0-7 points), medium (8-14 points), and high-risk (≥15 points) for CIH. The score is calculated as follows: age 80 or older (2 points), female (1.5 points), diabetes (3 points), urgent (PCI) (2.5 points), emergent PCI (3.5 points), congestive heart failure (4.5 points), serum creatinine of 1.3 to 1.9 mg/dL (5 points) or 2 mg/dL or greater (10 points), and pre-PCI use of intraaortic balloon pump (13 points). Preprocedural serum creatinine, congestive heart failure, and diabetes accounted for 76% of the predictive ability of this model. Based on the score, high-risk patients can be identified for early administration of more aggressive and intensive prophylaxis.

Withdrawal of Nephrotoxic Drugs

Common nephrotoxic drugs include nonsteroidal antiinflammatory drugs (NSAIDs), metformin, diuretics (e.g., furosemide), angiotensin-converting enzyme (ACE) inhibitors, aminoglycosides, sulfonamides, penicillin, amphotericin, cyclosporin A, vancomycin, and cisplatin. These agents should be withdrawn before contrast media administration in all patients at risk. Metformin in particular can produce intramedullar metabolic acidosis, which promotes nephropathy. Temporary suspension of diuretics on the day of the implant procedure is usually well tolerated.

Periprocedural Hydration

Hydration prevents acute kidney injury after contrast administration by increasing urine flow rate and limiting the time of contact between the contrast media and the tubular epithelial cells. Hydration has two considerations: (1) the fluid used: half-normal saline, normal saline, or bicarbonate, and (2) the protocol: “overnight” (12 hours before and 12 hours after) or “bolus” (3 mL/kg 1 hour before and 1-1.5 mL/kg 4-6 hours after procedure).

Hydration Fluids

Hypotonic saline.

A 0.45 normal saline (NS) solution (in 5% glucose) should not be used; it is less effective than isotonic saline. In a study of 1383 patients, the incidence of CIN was 2.0% with 0.45 NS versus 0.7% with isotonic saline.

Isotonic saline.

Multiple clinical trials confirm that hydration with 0.9% NS is highly effective at reducing the incidence of CIN. This is true for patients with preexisting diabetes or renal insufficiency. It is important to recognize that these studies were performed in patients undergoing coronary angiography and only a small percentage of patients had underlying severe LV dysfunction. Confirmation of the benefit of NS hydration in a patient population undergoing CRT implantation has not been rigorously tested.

Sodium bicarbonate.

Multiple trials have compared the use of sodium bicarbonate to saline hydration for the prevention of CIN. Although smaller, single-center studies have suggested a possible benefit of sodium bicarbonate infusion over isotonic saline, a metaanalysis of larger studies showed the incidence of acute kidney injury was equivalent [10.7% and 12.5%, respectively; relative risk (RR) 0.85 (0.63 to 1.16)].

Hydration Protocol

There are no direct comparisons of overnight versus bolus infusion. However, analysis of the bicarbonate versus saline trials suggests bolus hydration just prior to the procedure is superior to slow, overnight hydration. After filtration by the renal glomeruli, the concentration of the contrast agent increases to more than 100 times that in serum. If hydration fluid is infused at 1 mL/kg/hr for 12 hours, the concentration of the filtered contrast agent through the nephron is almost halved. If the infusion rate is increased to 5 mL/kg/hr, the concentration of the filtered contrast agent is reduced to about a tenth of the serum concentration. Ideally, in patients with congestive heart failure (CHF), the hydration regimen should be defined according to predefined clinical markers, such as urine flow rate, or left ventricular end-diastolic pressure. In patients with CHF, the total volume of fluid infused with bolus administration is often significantly less than even reduced-rate overnight hydration. It is therefore recommended to avoid overnight hydration and use acute hydration (3 mL/kg) starting 1 hour before the procedure, then either 1 mL/kg during and 6 hours after the procedure or 1.5 mL/kg for 4 hours. This protocol has the additional advantage of avoiding an unnecessary hospitalization prior to the planned procedure.

Volume of Contrast Media

Although studies show that the risk of CIN is dose-dependent, there does not appear to be a threshold value below which CIN does not occur. Patients with preexisting renal dysfunction and diabetes appear to be at highest risk for CIN. Studies have shown that the ratio of contrast volume to creatinine clearance (V/CrCl) predicts CIN in patients undergoing angiography procedures. A V/CrCl value of >4 was associated with a significant increased risk (adjusted OR 3.5, 95% confidence intervals 1.7-7.3; P < 0.001).

Choice of Contrast Agent

Types of Iodinated Contrast Agents

All contrast agents consist of a benzoic acid molecule with three atoms of iodine replacing hydrogen atoms on the benzene ring. Classification is based on (1) the charge on the iodinate molecule (ionic vs. nonionic), (2) molecular structure (monomer vs. dimer), and (3) osmolality. The osmolality of the contrast agents is a measure of the number of particles in solution as compared with the osmolality of plasma (290 mOsm/kg). These can be iso-osmolal (close to 290 mOsm/kg), low-osmolal (500-900 mOsm/kg) or high-osmolal (>1400 mOsm/kg). It is important to recognize that the term “low-osmolal” refers to contrast media with higher osmolality than an “iso-osmolal” agent due to naming conventions.

The original contrast agents were ionic monomers and very hypertonic (osmolality of metrizoate = 2100), whereas newer contrast agents are nonionic and less hypertonic (osmolality of iopamidol = 796). The osmolality of nonionic agents is as follows: iodixanol 290, ioxilan 695, iopromide 774, iopamidol 796, and iohexol 884 mOsm/kg. By current naming convention, iodixanol is iso-osmotic and the others are low-osmolar.

Comparison of Contrast Agent Nephrotoxicity

Ionic versus nonionic.

One randomized prospective evaluation of ionic diatrizoate (measured osmolality = 1500) versus nonionic iopamidol (osmolality 796) found no difference in the incidence of nephrotoxicity. However, the subsequent RECOVER study compared ionic, low-osmolar ioxaglate (osmolality 580) to nonionic, iso-osmolar iodixanol (osmolality 290) in patients with renal insufficiency undergoing coronary angiography with or without PCI. The incidence of nephropathy was significantly lower with iso-osmolar, nonionic iodixanol (7.9%) than with low-osmolar, ionic ioxaglate (17.0%) ( P = 0.021). Whether these findings reflect the difference in osmolality or ionic charge is not clear.

Low-osmolar nonionic versus iso-osmolar nonionic.

The Cardiac Angiography in Renally Impaired Patients (CARE) study was a prospective, multicenter, randomized, double-blind comparison of the low-osmolar, nonionic iopamidol (osmolality 796) to the iso-osmolar, nonionic iodixanol (osmolality 290) in high-risk patients. CIN, defined by multiple endpoints, was not statistically different in high-risk patients, with or without diabetes mellitus. All patients received prophylactic volume expansion with isotonic sodium bicarbonate solution, administered at 3 mL/kg/hr for 1 hour before angiography, and at 1 mL/kg/hr during and for 6 hours after angiography. Prophylactic N -acetylcysteine regimen of 1200 mg twice daily administered on the day before and on the day of the study procedure was used in some centers. The authors concluded that any true difference between the agents was small and unlikely to be clinically significant. Adequate hydration with saline or bicarbonate (3 mL/kg load, then 1 mL/kg for 6 hours) seems to reduce the difference (if any) among the different agents. When hydration is suboptimal, the nonionic agents, particularly those with an osmolality close to isotonic (iodixanol) may be superior.

Gadolinium.

Gadolinium (Gd) is a silvery-white, malleable, and ductile rare-earth metal. Gd has paramagnetic properties and, therefore, solutions of organic Gd complexes and Gd compounds are commonly used intravenously for magnetic resonance imaging (MRI) as contrast agents. It is a heavy metal element that attenuates x-ray photons.

Gadolinium (Gd) is a rare-earth metal with paramagnetic properties and is commonly used as an intravenous contrast agent for cardiac MRI (cMRI). Gd has been used in interventional procedures to visualize vascular structures; however, image quality may be suboptimal. Although they may be less nephrotoxic than iodinated contrast agents, Gd-based contrast agents should not be used in patients with renal insufficiency (eGFR < 30) because of their association with nephrogenic systemic fibrosis, a rapidly progressive fibrosing disorder of skin and internal organs.

Carbon dioxide.

For more than five decades, gaseous carbon dioxide (CO ₂ ) has been recognized by interventional cardiologists as an alternative to iodinated contrast for diagnostic as well as interventional procedures. Gaseous CO ₂ displaces blood and results in negative contrast; however, careful preparation is required to avoid air contamination. Winters et al described their favorable experience with gaseous CO ₂ venography rather than iodinated dye in patients undergoing pacemaker or ICD lead revisions.

Drugs to Prevent Renal Failure

N-Acetylcysteine

A potent antioxidant with vasodilator properties, N -acetylcysteine (NAC) may prevent acute renal dysfunction by scavenging a variety of oxygen-derived free radicals and improving endothelium-dependent vasodilation. Multiple clinical trials have looked at the use of NAC along with sodium chloride or sodium bicarbonate infusion for prevention of CIN with mixed results. In a large, randomized trial comparing NAC to placebo in patients with at least one risk factor for CIN, no difference in the incidence of acute kidney injury was found (12.7% NAC vs. 12.7% placebo, relative risk, 1.00; 95% confidence interval, 0.81 to 1.25; P = 0.97). Although not mandated in this trial, hydration with isotonic saline or sodium bicarbonate infusion was performed in 98% of patients in both arms. In general, NAC should not be used as a substitute for hydration for prevention of CIN, even in the presence of CHF.

Ascorbic Acid

An early study reported that the antioxidant ascorbic acid (administered as 3 grams 2 or more hours before, 2 grams the night after, and 2 grams the morning after angiography or intervention) significantly reduced the risk of contrast-mediated renal dysfunction compared with placebo. A subsequent metaanalysis of nine randomized trials demonstrated that patients receiving ascorbic acid had 33% less risk of CIN compared with placebo or alternative pharmacological treatment (risk ratio 0.67; 95% confidence interval, 0.466 to 0.969; P = 0.034).

HMG-CoA Reductase Inhibitors (Statins)

Multiple studies have shown a reduction in the incidence of CIN in patients either chronically or acutely administered statin medications prior to coronary angiography procedures. In a metaanalysis of patients acutely given statins, there was a nearly 50% reduction in CIN compared with placebo (4.0% vs. 7.4%; 95% CI, 0.40 to 0.71; P < 0.0001). These effects appear comparable with all statin types (lipophilic or hydrophilic); however, high-dose statin administration appears more effective than low. A typical regimen would be rosuvastatin 10 mg given 2 days prior and 3 days after the procedure. Overall, the effect of statins to reduce the incidence of CIN appears to be greatest in patients at highest risk (CHF, chronic kidney disease, diabetes).

Hemofiltration and Hemodialysis

In patients with a creatinine greater than 2 mg/dL, hemofiltration (4 hours before and continued for 24 hours after the procedure) compared with isotonic saline prevented the deterioration of renal function, decreased the need for renal replacement therapy, and improved in-hospital and long-term outcomes. Similarly, in patients with a serum creatinine more than 3.5 mg/dL, hemodialysis (a single, 4-hour treatment initiated immediately after procedure) reduced length of stay and the need for renal replacement therapy at hospital discharge. Both hemofiltration and hemodialysis require significant hospital resources, however.

Forced Diuresis

Effective reduction in CIN with hydration involves not just the proper fluid, but the proper volume as well. Extracellular volume (ECV) expansion serves to prevent activation of the renin-angiotensin-aldosterone system and reduce the impact of renal vasoconstriction induced by contrast media. Adequate urine flow serves to dilute the concentration of contrast within the renal tubule lumen and decrease its contact time with renal tubule cells. Medications that force diuresis (furosemide, mannitol) without adequate ECV expansion have failed to reduce the incidence of CIN and in fact may be harmful. Recently, a strategy to achieve a high urine output while maintaining euvolemia has been developed (RenalGuard, PLC Medical Systems, Millford, MA). A urinary collection bag is used and the volume of infused fluid is automatically matched to the volume of excreted fluid (measured each second). By administering a small bolus of fluid initially (3 mL/kg) and initiating diuresis with a small dose of furosemide (0.25 mg/kg), urine output increases significantly in about 1 hour and can be sustained for 6 hours usually without additional diuretic administration. Compared with standard hydration protocols, use of the RenalGuard system resulted in a 53% reduction in the incidence of CIN in patients with significant risk for acute kidney injury.

Allergic Reactions

A variety of regimens are used to prevent allergic reactions to iodinated contrast agents. Specific regimens will vary from center to center. Preprocedure medications include a histamine receptor blocker (diphenhydramine) and steroids. Typically, prednisone or methylprednisolone is administered 12 hours and immediately before the procedure.

No data suggest that shellfish allergies predict increased risk of adverse reactions to contrast. It is currently thought that shellfish allergy is related to tropomyosin, and patients with seafood allergies do not have an increased risk of iodine allergy.

Conclusion

Contrast nephropathy results in an increased length of stay, higher morbidity, and both short-term and long-term mortality. Proper and adequate hydration is the cornerstone of preventive treatment for CIN. Implanting physicians may be concerned with CHF decompensation with fluid administration; however, fluid boluses given just before and for a few hours after the procedure can be safely administered. Box 32-3 shows the approach that should be taken in all patients undergoing CRT implantation where there is anticipation of contrast use.

Box 32-3

Steps to Prevent Contrast Nephropathy

1.
Withdraw nephrotoxic drugs.
2.
Bolus hydration with either isotonic saline or bicarbonate, 3 mL/kg/hr for 1 hour before, then 1 mL/kg/hr (consider 0.5 mL/kg/hr for recent congestive heart failure [CHF] decompensation) during and for 6 hours after the procedure. Because the total volume of intravenous (IV) hydration is lower with bolus hydration and the results possibly better, overnight hydration is not recommended particularly for those with CHF.
3.
Consider oral N -acetylcysteine, ascorbic acid or statin.
4.
Use either iso-osmolar iodixanol or low-osmolar iopamidol.
5.
Consider hemofiltration, hemodialysis or matched extracellular volume expansion (RenalGuard) in high-risk patients.

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