Response by Patel et al to Letter Regarding Article, "Perioperative Cerebral Microbleeds After Adult Cardiac Surgery"

Neurological impact of emboli during adult cardiac surgery

Objectives

This study draws on advances in Doppler ultrasound bubble sizing to investigate whether high volumes of macro-bubbles entering the brain during cardiac surgery increase the risk of new cerebral microbleeds (CMBs), ischemic MR lesions, or post-operative cognitive decline (POCD).

Methods

Transcranial Doppler (TCD) ultrasound recordings were analysed to estimate numbers of emboli and macrobubbles (>100 μm) entering the brain during cardiac surgery. Logistic regression was used to explore the hypothesis that emboli characteristics affect the incidence of new brain injuries identified through pre- and post-operative MRI and neuropsychological testing.

Results

TCD, MRI, and neuropsychological test data were compared between 28 valve and 18 CABG patients. Although valve patients received over twice as many emboli per procedure [median: 1995 vs. 859, p = .004], and seven times as many macro-bubbles [median: 218 vs. 28, p = .001], high volumes of macrobubbles were not found to be significantly associated with new CMBs, new ischaemic lesions, or POCD. The odds of acquiring new CMBs increased by approximately 5% [95% CI: 1 to 10%] for every embolus detected in the first minute after the release of the aortic cross-clamp (AxC). Logistic regression models also confirmed previous findings that cardiopulmonary bypass time and valve surgery were significant predictors for new CMBs (both p = .03). Logistic regression analysis estimated an increase in the odds of acquiring new CMBs of 6% [95% CI: 1 to 12%] for every minute of bypass time over 91 mins.

Conclusions

This small study provides new information about the properties and numbers of bubbles entering the brain during surgery, but found no evidence to substantiate a direct link between large numbers of macrobubbles and adverse cognitive or MR outcome.

Clinical Trial Registration URL - http://www.isrctn.com. Unique identifier: 66022965.

•

Higher numbers of macrobubbles enter the brain during valve surgery compared to bypass graft surgery.

•

Macrobubbles did not appear to be linked to new cerebral microbleeds, ischemic lesions, or cognitive decline.

•

Emboli received following release of the aortic cross-clamp predicted new cerebral microbleeds.

•

Other factors predicting new microbleeds included cardiopulmonary bypass duration and surgery type.

Prevalence and Evolution of Susceptibility-Weighted Imaging Lesions in Patients With Artificial Heart Valves

Background

In patients with mechanical heart valves, cerebral susceptibility‐weighted imaging (SWI) lesions on magnetic resonance imaging, postulated to be caused by degenerative metallic abrasion, are frequently referred to as valve abrasion. It remains unclear whether valve implantation not requiring cardiopulmonary bypass or biological heart valves also shows those lesions.

Methods and Results

Two blinded readers rated SWI lesions and cerebral amyloid angiopathy probability according to established criteria on brain magnetic resonance imaging pre‐ and postinterventionally. We assessed the association between valve type/cardiopulmonary bypass use and SWI lesion count on the first postinterventional scan using multivariable logistic regression. On postinterventional magnetic resonance imaging, 57/58 (98%) patients with mechanical heart valves had at least 1 and 46/58 (79%) 3 or more SWI lesions, while 92/97 (95%) patients with biological heart valves had at least 1 and 72/97 (74%) 3 or more SWI lesions. On multivariate analysis, duration of cardiopulmonary bypass during implantation significantly increased the odds of having SWI lesions on the first postinterventional magnetic resonance imaging (β per 10 minutes 0.498; 95% CI, 0.116–0.880; P=0.011), whereas valve type showed no significant association (P=0.338). Thirty‐seven of 155 (23.9%) patients fulfilled the criteria of possible/probable cerebral amyloid angiopathy.

Conclusions

SWI lesions in patients with artificial heart valves evolve around the time point of valve implantation and the majority of patients had multiple lesions. The missing association with the valve type weakens the hypothesis of degenerative metallic abrasion and highlights cardiopulmonary bypass as the main risk factor for SWI occurrence. SWI lesions associated with cardiac procedures can mimic cerebral amyloid angiopathy. Further research needs to clarify whether those lesions are associated with intracranial hemorrhage after intravenous thrombolysis or anticoagulation.