Preexisting Thrombocytopenia Worsens Complications After TAVR

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Patients undergoing transcatheter aortic valve replacement (TAVR) have decreases in platelet counts that are typically transient, lasting just a few days. But in those with preexisting thrombocytopenia, a major decrease in platelets resulting from the procedure puts them at risk for worse in-hospital outcomes, according to a single-center study published online September 30, 2014, ahead of print in Catheterization and Cardiovascular Interventions.

Preexisting Thrombocytopenia Patients Fare Worse

Following TAVR, patients were divided into 1 of 3 groups by thrombocytopenia status:

• None: nadir platelet count within normal reference range
• Newly Acquired: either mild (100-149 x 10³ cells/µL) or moderate-severe (< 100 x 10³ cells/µL)
• Preexisting: either mild or moderate-severe

Thirty-six patients (40%) had preexisting thrombocytopenia. These patients had lower BMI than those without thrombocytopenia and were less likely to be current smokers (P < .05 for both).

Prior to TAVR, mean platelet count was 293 x 10³ cells/µL in the group without thrombocytopenia, 214 x 10³ cells/µL in the group with TAVR-acquired thrombocytopenia, and 110 x 10³ cells/µL in the group with preexisting thrombocytopenia.

Patients in all 3 groups had decreases in post-TAVR platelet counts. Compared with baseline, patients with no thrombocytopenia and those with acquired thrombocytopenia had platelet counts that were 25% and 99% lower, respectively, the day after TAVR. By day 6, however, patients in both groups experienced a rebound in platelet counts to nonthrombocytopenic levels. By day 7, all groups—including those with preexisting thrombocytopenia—demonstrated a complete recovery of platelet counts or had levels that were at least higher than those at baseline. Nadir in platelet counts occurred at day 4 post-TAVR in all 3 groups (tables 1 and 2).

Table 1. Platelet Counts Day 4 by Thrombocytopenia Status

Table 2. Platelet Counts Day 8 by Thrombocytopenia Status

When further examined by severity, the number of patients who developed moderate-to-severe thrombocytopenia increased each day after the procedure, peaking at day 4, and decreasing thereafter with platelet recovery occurring by day 6.

On multivariable analysis, baseline predictors of moderate-to-severe thrombocytopenia in patients with acquired or existing low platelets were:

• Baseline thrombocytopenia
• Leaner body mass
• Smaller preprocedural aortic valve area
• Higher peak aortic jet velocity
• Worsening baseline renal function

Additionally, in those with preexisting thrombocytopenia, development of moderate-to-severe thrombocytopenia (nadir platelet count < 100 x 10³ cells/µL) predicted a higher risk of major vascular complications (OR 2.78; 95% CI 1.58-3.82) and major bleeding (OR 3.18; 95% CI 1.33-5.42).

Causal Relationship Unclear

The study authors note that while data on the causal relationship between TAVR and thrombocytopenia are limited, some studies have suggested that postprocedural bone-marrow suppression and/or sequestration may be responsible. It also has been demonstrated that ongoing mechanical platelet destruction following surgical aortic valve replacement results directly from the implanted bioprosthesis, Dr. Flaherty and colleagues say, noting that the occurrence of thrombocytopenia after balloon aortic valvuloplasty is both less severe and less frequent than after TAVR or surgery.

Other possible causes are acute drug-related complications after TAVR—particularly with thienopyridine use—and aberrant von Willebrand factor metabolism in patients with severe aortic stenosis. The study authors suggest “further investigation of putative mechanisms such as bone-marrow suppression and platelet sequestration is required as no patient underwent bone-marrow aspiration, biopsy, or examination of in vivo platelet sequestration in this study.”

While Dr. Flaherty and colleagues say it is “tempting” to speculate about links between procedural variables and TAVR-related thrombocytopenia, few data exist to support this theory. Additionally, they note that because no clear definition of “major thrombocytopenia” exists to guide management of these patients, a nadir platelet count < 100 x 10³ cells/µL should be applied to define clinically relevant thrombocytopenia, especially in those with preexisting low platelet count.

Source: 
Flaherty MP, Mohsen A, Moore JB, et al. Predictors and clinical impact of pre-existing and acquired thrombocytopenia following transcatheter aortic valve replacement. Catheter Cardiovasc Interv. 2014;Epub ahead of print. 

Disclosure:

• Dr. Flaherty reports no relevant conflicts of interest. 

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