ECHOCARDIOGRAPHIC CONTRAINDICATIONS FOR CARDIOVERSION

The identification of left atrial (LA) or LA appendage (LAA) thrombus by transesophageal echocardiography (TEE) is a contraindication for elective transthoracic electrical cardioversion (TEC) in patients with AF because of the risk of a thromboembolic event (TE), primarily stroke [Fuster V et al. Europace 2006].

Thrombus is defined as an echodense lesion that is present in multiple imaging planes and is clearly distinguishable from trabeculation and atrial endocardium. A thrombus is detected by TEE in 10% to 15% of patients with AF, and <1% of these patients have a TE after cardioversion. Ali Oto, MD, Hacettepe University, Ankara, Turkey, noted that patients with a left atrial thrombus should be treated with anticoagulation for 3 to 4 weeks and then have a repeat TEE examination to determine suitability for TEC.

The presence of sludge on TEE, which is defined as a dynamic and gelatinous but not solid or well-formed echodensity that is present throughout the entire cardiac cycle [Troughton RW et al. Heart 2003], is a situation in which the physician must decide how to respond, because no studies have been conducted to determine the safety of TEC in this population. A retrospective 10-year survey of 2705 patients with AF who underwent TEE showed that the prevalence of LA or LAA sludge was approximately 2% [Yarmohammadi H et al. J Am Soc Echocardiogr 2012]. Furthermore, this study found no difference in the rate of TE in patients with LA or LAA thrombus or sludge as compared to patients without LA or LAA thrombus or sludge (about 4% in both groups).

Another finding on TEE, spontaneous echo contrast (SEC), is not a contraindication for TEC, but patients should receive prior therapeutic anticoagulation if possible, according to a review of 9 clinical studies [Patel SV, Flaker G. Clin Cardiol 2008]. SEC is defined as a swirl or smoke that is associated with low blood flow velocity [Troughton RW et al. Heart 2003], and it has 4 grades depending on its intensity, its location, and the presence of swirling movement [Patel SV et al. Clin Cardiol 2007].

REMOTE DEVICE MONITORING TO REDUCE STROKE RISK

Atrial arrhythmias recorded by cardiac implantable electronic devices (CIEDs) are an independent predictor of total mortality, stroke, and chronic AF [Glotzer TV et al. Circulation 2003]. Atrial high rate episodes (AHREs) were recorded in the memory of ∼50% of CIEDs during the battery life span in this study, and most were asymptomatic. The level of AF burden that increases risk appears to vary among studies, ranging from 3.8 hours per day, associated with a 2.0% rate of TE (p=0.006) [Shanmugam N et al. Europace 2012], to ≥5.5 hours daily, associated with a 2.4% of TE (HR, 2.20; 95% CI, 0.96–5.05; p=0.06) [Glotzer TV et al. Circ Arrhythm Electrophysiol 2009]. Device-detected AHREs were associated with an increased risk of TE and stroke, regardless of the predevice history of AF [Shanmugam N et al. Europace 2012].

A risk stratification schema created by combining device-detected AHREs and clinical data provides another approach to assist in defining patients at low or high risk for stroke (Figure 2) [Botto GL et al. J Cardiovasc Electrophysiol 2009]. Yet refinement of this schema with additional evidence is needed to determine when anticoagulation should be initiated, stated Renato P. Ricci, MD, S. Filippo Neri Hospital, Rome, Italy. After anticoagulation is initiated, it should not be discontinued even in the absence of device-detected AF.

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Figure 2.

Risk Stratification Schema Using Clinical Data and Device-Detected Events

AF=atrial fibrillation; AT=atrial tachycardia; FU=follow-up; MDT=Medtronic.Reproduced from Botto GL et al. Presence and duration of atrial fibrillation detected by continuous monitoring: crucial implications for the risk of thromboembolic events. J Cardiovasc Electrophysiol 2009;20(3):241–248. With permission from John Wiley and Sons.

Remote monitoring (RM) of CIEDs is being investigated to reduce TE risk. Only one randomized study has been reported, however, which was terminated early due to futility. The Combined Use of BIOTRONIK Home Monitoring and Predefined Anticoagulation to Reduce Stroke Risk study [IMPACT; NCT00559988] showed no difference at 5 years in the primary end point of first stroke, systemic embolism, or major bleed between the RM and usual-treatment patients (2.4 vs 2.3 event rate, respectively; HR, 1.06; p=0.732). The rate of major bleeding was 1.2 and 1.6, respectively, in the control (n=1361) and RM (n=1357) groups, compared with 0.1 for hemorrhagic stroke in both groups, noted Prof. Ricci. In the RM group, only 4.5% of patients who had appropriate anticoagulation (an international normalized ratio [INR] of 2 to 3) had an ischemic stroke, compared with 95.5% of those with an INR <2. This low stroke event rate may have limited the ability to detect a difference with remote monitoring, said Prof. Ricci. Furthermore, device-detected AF was found in only 35% to 50% of patients prior to stroke, and this was within 30 days of the stroke in only 8% to 22% of patients [Brambatti M et al. Circulation 2014; Daoud EG et al. Heart Rhythm 2011]; thus, this temporal dissociation is an emerging issue that must be explored.