Cardiac resynchronization therapy (CRT) improves symptoms, quality of life and reduces hospitalization in patients with New York Heart Association (NYHA) class III-IV classification and left bundle branch block.1,2 Inaddition,implantation of a CRT system with or without defibrillator reduces mortality in this patient population.3,4 More recently, CRT was shown to reduce heart failure progression and induce left ventricular reverse remodeling in patients with NYHA class I and II symptoms.5,6 In this article, we will review the techniques used at Emory University Hospital Midtown for CRT implantation as well as tips for a successful and safe procedure. Implant Techniques Venous Access A left subclavian venous access is the preferred venous entry to cannulate the coronary sinus (CS) because it provides a more natural curve for the guide catheter to follow from the shoulder to the CS os. A right-sided subclavian venous entry is used at times when upgrading an existing system or when the left subclavian vein is occluded. In the case of a new implant we routinely use the cephalic vein to place the right atrial (RA) and right ventricular leads (RV), but we use a subclavian vein puncture to provide a separate access site for the left ventricular (LV) lead. By placing the RV lead first, we provide back-up pacing in case instrumentation of the right bundle branch by the guide catheter or the wire results in complete heart block in patients with preexisting left bundle branch block (LBBB). When upgrading a pacing system, a venogram of the subclavian vein is routinely performed in order to guide the implant procedure. In the case of an occluded vein, one could implant an LV lead in the contralateral shoulder and tunnel the lead to the old system. Alternatively, abandoning the old system and implanting a new one on the contralateral shoulder could be done. A third option is to sacrifice one of the old leads to serve as a rail for a laser assisted extraction and create venous access to replace the old lead and add a new LV lead. CS Access In patients with heart failure and dilated RA or LV, the CS ostium location is distorted and usually lower and more posterior. Several fluoroscopic landmarks could be used to localize the CS. In the right anterior oblique (RAO) view, the lucent “fat-pad” overlying the atrial-ventricular groove marks the course of the CS. Other markers such as calcification of the right coronary artery could also serve as a guide to the CS. The left anterior oblique (LAO) view best guides CS entry since in this view the CS runs toward the spine to encircle the mitral annulus.7 We usually access the CS in the AP view utilizing a 3-step approach:7 • Step 1: advance the guide to the lower right atrium with the tip pointing to the cardiac apex, and once in this position, pull the guidewire into the guide • Step 2: bounce the guide off the RA floor until the tip points upward • Step 3: counterclockwise rotation usually points the tip posterior to cannulate the CS ostium. At this stage, you probe with the guidewire to confirm CS location. When multiple attempts using the traditional approach fail to cannulate the CS, standard angiographic diagnostic catheters could be used by inserting them inside the guide to help access the CS. The multipurpose catheter (MP-A2) extends the reach of the guide catheter and allows more maneuverability. Simple rotation of the MP-A2 allows the tip to point up or down and could help engage the CS. The Amplatz-2 or 3 (AL-2 or AL-3) catheter is helpful in our experience in patients with severely dilated RA, since it extends the reach of the guide catheter and allows upward direction of the guidewire toward an upwardly angulated CS (Figure 1). We recommend performing CS venography in all patients to delineate the location and size of the available coronary veins.We usually target the lateral branch as our first option followed by the pos- terolateral or anterolateral CS vein. Sometimes no apparent CS veins drain- ing the lateral LV wall are seen. In this situation, a closer inspection of the venogram will reveal the presence of a posterior interventricular vein (PIV) with a large branch supplying the lateral LV wall. The left internal mammary artery catheter (LIMA) is very helpful in this set- ting to subselect the PIV branch, and by advancing an angioplasty wire up the lat- eral branch, a LV lead could be delivered to the lateral LV wall and could be used for CRT (Figures 2A and 2B). LV Lead Insertion It is very important when choosing a LV lead to use one that matches the size of the targeted LV branch, since this will minimize micro- or macrodislodgement. We use over-the wire (OTW) LV leads in the majority of cases; stylet-driven leads are rarely used and are reserved for large target veins where large leads should be used. The OTW approach allows for targeting different branches and helping subselect small tributaries to achieve optimal lead stability and avoid phrenic nerve stimulation. A guidewire (0.014 inch intermediate weight) is loaded into the lead after shaping the distal tip (40o- 60o). The lead and the wire are advanced into the guidewire. The wire is manipulated into the desired branch and advanced as distally as possible. Sometimes valves within the CS, tortuous veins or veins that originate at an acute angle (>120o), will prevent passing the wire and/or lead into the desired branch. In this situation, a LIMA catheter is used to engage the desired branch; a heavyweight wire (0.014-0.016 inches) is advanced through the LIMA catheter into the branch, and fine manipulation is used to advance the guidewire as distally as possible (Figure 3). The heavyweight wire straightens the curves or the acute angle and allows the lead to be advanced over the wire. Advancing the lead while pulling the wire (the “push-pull” technique) helps wedge the lead into a small branch and create a stable lead position. Once the lead is in position, diaphragmatic stimulation is tested by pacing at 10 Volts, sometimes asking the patient to take deep breaths during high output pacing. Then capture threshold is determined. As will be discussed later, a large window between diaphragmatic and myocardial capture threshold should be obtained. Implant Complications and Success LV Lead Dislodgement Despite the advancement in lead design and the larger CRT implant, LV lead dislodgement remains a common complication of this procedure. It has been reported in 5.8% (7.7% if exit block and diaphragmatic stimulation possibly related to microdislodgement are included) of implants in the MIRACLE study group, in 5% in the CARE-HF trial and in up to 12% in the Multisite Stimulation in Cardiomyopathies (MUSTIC) trial.2,6,8 This commonly encountered problem is probably related to the complexity of the CS anatomy and its branches and the available lead design. For instance, some leads have an inherent secondary curve which could lead to delayed dislodgement, despite extra care taken during the implant to wedge the lead as distally as possible. In addition, even though large CS branches would easily fit a large lead, they are also more prone to have LV lead dislodgement if the LV lead is not wedged in a small tributary. Some tips to minimize this complication include: • Using a large LV lead when targeting large CS branches • Wedging the LV lead in a small tributary and as distally as possible • Verifying lead position in 2 orthogonal x-ray views for less experienced operators to make sure that the lead has adequate “slack”. Phrenic Nerve Stimulation The left phrenic nerve courses along the lateral aspect of the LV. Hence, phrenic nerve capture is most likely to occur when pacing the lateral LV wall via a lateral CS branch (the most targeted site for CRT). In fact, the MIRACLE study group reported that diaphragmatic stimulation occurred in 0.8% of cases in the preoperative period and in 1.2% of cases in the postoperative period (discharge to 6 months). Chronically, diaphragmatic stimulation occurs in 1.6- 12% of patients.9 Most of these cases could be managed non-invasively by lowering the pacing output or by changing the LV pacing vector characteristics (“electronic repositioning”). Diaphragmatic stimulation requires surgical repositioning of the LV lead in 1.7- 2.2% of cases, as recently reported by the CARE-HF and REVERSE trials.4,5 Because diaphragmatic stimulation is fairly common, it should be assessed carefully at the time of implant. Careful monitoring for diaphragmatic stimulation during high-output pacing (10 Volts) should be performed every time a new position is targeted. Asking the patient to take a deep breath while pacing at high output could reveal evidence of diaphragmatic stimulation that is not apparent otherwise. One should not accept a LV lead position that results in a narrow window between diaphragmatic stimulation and myocardial capture threshold for two main reasons: • Diaphragmatic stimulation could be absent or minimal during the procedure when the patient is supine, but becomes evident with change in body position • Microdislodgement of LV leads is relatively common, and minimal changes in LV lead position could lead to significant diaphragmatic stimulation. CS Dissection or Perforation CS dissection could result from trauma from guidewire manipulation, guide catheter manipulation or forceful movement of the balloon-tipped venography catheter, or as a result of aggressively advancing the LV lead against resistance. Even forceful injection of contrast against the CS wall could lead to CS dissection. Most CS dissections or perforations are clinically silent because of the low pressure venous system. In addition, the pericardium and adipose tissue, in the atrial-ventricular groove where the CS lays, help contain the low pressure venous bleeding. In the MIRACLE study program, CS dissection occurred in 45 patients (2.2%); 6 (13%) of those required drainage for pericardial tamponade and none required surgery or died. In addition, 21 out of the 45 (46.7%) still received a CRT implant during the same procedure. Similarly, the rate of CS dissection or perforation was also low in the CARE-HF trial (2.1%). Three of those patients (30%) developed pericardial effusion. Avoiding any forceful catheter or wire manipulation could minimize CS dissection or perforation; even contrast injection should be done with care to avoid this complication. It is our experience that LV lead implantation could be done safely despite CS dissection during the same session. Usually, targeting a branch proximal to the dissection plane is the safest approach (i.e., cannulating a posterolateral branch after a mid CS body dissection). In some cases, maneuvering the wire in the true lumen in order to bypass the dissection plane and reach a distal CS branch could be done at the risk of extending the dissection. In few instances, aborting the procedure and attempting it a few weeks later, allowing time for the CS dissection to heal, is the only possible safe approach (i.e., when the dissection is at the level of the only available branch). Implantation Success Rates In a report of over 2,000 patients under- going CRT, an implant success rate was achieved in 1,903 out of 2,078 patients (91.6%).8 Thirty-five of those patients (1.8%) required more than one procedure to achieve a successful implant. Similar outcomes were achieved in the CARE-HF trial. In this trial, success rates after the first procedure were 89% (349 out of 404 patients). However, overall success after 2 or 3 procedures was 95.6% (390 out of 404 patients). In both of these trials, the inability to access the CS was the most common reason for the unsuccessful procedure (39.4-42.8%), followed by the inability to obtain stable lead position (33%). Experience seems to be the major determinant of success, with the first-time success rate at 90% in experienced centers participating in the CARE-HF study versus 82% in inexperienced centers. In high-volume centers and in the era of OTW LV leads, success rates are reported to be higher (e.g., 98% in a single-center experience7). Conclusion CRT has gained widespread use as an adjunctive therapy to heart failure patients on optimal medical therapy. The success rate of this procedure improves with experience, and is likely to improve with the availability of newer delivery systems and newer lead technology. References
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