Fig. 15.1
Cumulative probability of HF or death by treatment arm in women (a) and men (b). The numbers in the parentheses indicate Kaplan–Meier event rates. CRT‐D indicates cardiac resynchronization therapy with defibrillator, HF heart failure, ICD implantable cardioverter–defibrillator (Adapted from Biton et al. [7])
15.1.2.1 Reasons for Gender-Specific LV Remodeling Response to CRT
Although we know more about heart failure physiopathology, there is much we do not understand about the physiologic mechanisms that underlie its sex differences.
A different hypertrophy pattern between genders was described, and this was verified also in postinfarction end-stage failing hearts [8]. Moreover, in failing human hearts, a higher myocyte death (necrosis or apoptosis) has been clearly demonstrated in men than in women [9]. Finally, it is well known that inherent physiological sex differences of abnormal conduction exist. It has been suggested that women have shorter QRS duration than men in the absence of any conduction disturbance. Some studies showed that women had significantly shorter baseline QRS durations, but they gained even greater clinical benefit from CRT‐D than men, suggesting that women may have more dyssynchrony, at shorter QRS durations, that leads to better response with CRT‐D [10].
All these data and observations suggest that gender directly affects physiologic and pathologic myocardial remodeling and that female gender provides a favorable substrate for LV reverse remodeling during CRT.
15.1.2.2 Reasons for Female CRT Undertreatment
In women, the proportion of responders defined on the basis of LVESVi reduction of at least 10 % was significantly higher, and the degree of reverse remodeling was also significantly greater than in men.
Despite this better outcome, women accounted for only 20 % of patients undergoing CRT implantation. This may be due to several factors. Women have less systolic dysfunction than men and are therefore more often treated by generalists. Women are not referred to a hospital as often as men and generally tend to undergo fewer invasive and noninvasive procedures as assessment of LV function.
Finally fewer women than men received ICDs, despite a similar degree of LV remodeling. This might be related to fewer women who fulfilled the MADIT II criteria and the underutilization of resources in women. On the other hand after the SCD-HeFT [11], there is a clear class I indication for ICD implantation for nonischemic dilated cardiomyopathy that is more common in women.
15.2 Implantation Techniques
15.2.1 Vein Accesses in Women
CRT implantation in women is achieved in a standard fashion, but some specific anatomical features should be taken into account. Because of the smaller vein size in women and the requirement of three leads placement for biventricular pacing—an atrial lead, a right ventricle (RV) lead (defibrillation or pacing), and a left ventricle (LV) pacing lead—it is worthwhile attempting cephalic and subclavian access in these cases. If possible, the right ventricular lead should be placed through a cephalic approach to minimize the potential for subclavian crush of the larger lead. The subclavian vein can then be used for introduction of the atrial lead and a LV lead via the coronary sinus (CS).
15.2.2 Right Ventricle Features in Women
In order to have correct defibrillator lead placement, it is necessary to keep the whole RV-defibrillating coil in the RV. This goal could not be easier to achieve in women patient with small cardiac volumes. The coil must not cross the tricuspid valve leaving a portion of it in the right atrium, avoiding defibrillation capacity deficiency and inappropriate diagnosis of ventricular arrhythmias during atrial tachyarrhythmias. Overcoming this problem may not always be compatible with choosing an optimal RV pacing site, which, for example, may be the mid-septum or another non-apical position. As the septum often bulges into the RV due to huge LV dilatation, the coil may lie partly in the right atrium. The implanter is then forced to select a less optimal site from the hemodynamic point of view in order to achieve effective arrhythmia diagnosis and defibrillation.
15.2.3 Coronary Sinus Anatomy
The CS ostium is partially covered by a Thebesian valve (a remnant of the embryonic right valve) in roughly 60 % of patients. In a small subset of patients, the ostium is completely enclosed by the valve with only small fenestrations allowing venous drainage, thereby presenting a major impediment to CS access. In addition, RA dilation may lead to an abnormally high insertion of the CS ostium, making its intubation difficult. A second valve (the valve of Vieussens) located at the junction of the great cardiac vein and the vein of Marshall is present in about 8 % of patients [12]. This valve may divert a wire or catheter into the diminutive vein of Marshall, which if not immediately recognized can lead to venous dissection and hemopericardium.
Anatomic studies have shown a median of six veins from the left ventricle draining into the main CS. The nearest branch to the CS ostium is the middle cardiac vein (MCV), which may be covered by a small valve or originate with a separate ostium. The MCV runs in the interventricular groove toward the ventricular apex and is usually not a suitable target for LV lead placement. Three distinct veins drain the lateral wall of the left ventricle (Fig. 15.2). The posterolateral branch, the most prominent and consistent of these veins, usually enters the CS within 1 cm of the ostium. The lateral marginal vein and lateral branches off the anterior interventricular vein (AIV) are variably present. In women with prior myocardial infarction, first-order branches to the lateral wall off the CS are often diminutive or absent.
Fig. 15.2
Selecting vein for LV lead placement. The possible targets for the left ventricular lead showed by the scheme in (a) free wall are (A) lateral (marginal) cardiac vein, (B) posterolateral cardiac vein, and (C) posterior cardiac vein. Suboptimal lead locations are also (D) middle cardiac vein and (E) great cardiac vein. In (b) an example of CS angiography and in (c) the leads’ final position are shown
One of the important elements in a successful implantation is selecting the most appropriate vein to cannulate for CRT lead placement. The best performance for LV pacing is thought to occur in a lateral or posterior–lateral position. This region was accessible from at least two CS tributaries (posterolateral and AIV) in greater than 85 % of patients. In approximately 20 % of patients, the mid-lateral LV wall was also accessible from branches of the MCV.
15.2.4 Coronary Sinus Variability
As proved by several CS angiograms, there is a great variability in CS anatomy (Fig. 15.3), and this matters during the LV lead placement. Rotational venography may provide a more complete assessment of the CS branches to help determine the best viewing angle for target branch access. Multislice computed tomography (CT) scan has been used preprocedure to assess the cardiac vasculature prior to the implant procedure and correlates well with occlusive venograms. In addition, CT may reveal a high CS ostium takeoff and aid in catheter selection for successful CS access [13].
Fig. 15.3
Different angiograms show the great variability in CS anatomy (Adapted from CS venograms. Adapted from CS venograms collection, Bongiorni MG, De Lucia R (with permission))
15.2.5 Interventional Approach to LV Lead Placement
The technique for LV lead placement includes the following steps: (1) localization of the CS ostium via contrast puffs through a preformed guide catheter, (2) cannulation of the CS with a sheath advanced over the guide catheter (with or without wire support), and (3) advancement of the LV lead through the delivery guide over an angioplasty wire.
The failure rates for placement of leads via the CS ranged between 7.5 and 10 % [14]. Most of these implant failures are due to difficulty accessing the CS ostium or advancing the pacing lead into an adequate, stable position. Coronary veins are still occasionally inaccessible and, more importantly, may not be present at the optimal stimulation site. In addition, LV lead dislodgement may occur both acutely or in the first few months after implantation in 6 % [15].
This issue underlines the need for designing specific implant tools which would allow (1) easier access to the CS, (2) a means of visualizing the CS branches, and (3) maneuverability of the pacemaker lead.
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- 1.
The development of preshaped sheaths that follow the curvature of the lateral wall and floor of the RA allows easier access to the CS. In addition, the development of dual, telescoping catheters of various shapes allows improved maneuverability and access to CS side branches [16]. Small injections of contrast through these catheters allow direct visualization of the CS ostium and target branches and speed implant time.
- 2.
Coronary sinus angiography greatly facilitates identification of a suitable branch vessel. Guiding sheaths and balloon catheters specifically designed for this purpose are available. Coronary sinus angiograms, preferably using right anterior oblique (RAO) and left anterior oblique (LAO) projections, should be recorded for reference during lead positioning (Fig. 15.4).
