Left atrial volume is significantly underestimated on TTE images, and TTE estimates have moderate correlation with left atrial volume measured with MDCT. Measured and estimated left atrial volumes at MDCT can provide important additive prognostic information in the care of patients undergoing MDCT for other reasons. Future studies are needed to obtain normative MDCT measurements of left atrial volume.

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electrophysiology-clinical, electrocardiogram Case PresentationA 62-year-old man presented with left hemiparesis resulting from a right internal capsule stroke. He reported irregular palpitations over the last month but denied lightheadedness or syncope. Echocardiography revealed normal left ventricular function. Figure 1 shows electrocardiographic recordings during his hospitalization. What are the mechanisms for the findings observed on these tracings? DiscussionThe underlying atrial rhythm is sinus with intermittent atrioventricular (AV) block in the setting of alternating right and left bundle branch block (BBB). The tracings show several repetitive but important patterns: (1) PR intervals are shorter with left BBB (LBBB) than right BBB (RBBB); and PR intervals progressively prolong with RBBB before AV block (Wenckebach), (2) LBBB always follows the long pause terminating AV block and starts each Wenckebach cycle, (3) P waves (*) falling into the T wave of the preceding QRS complex (which itself had followed a long PR interval of 280-420 ms) conduct to the ventricle with a paradoxically shorter PR interval (140-200 ms). Earlier-timed P waves landing on the downstroke of the negative T wave (lead V1) conduct with RBBB, while latertimed P waves falling on its upstroke conduct with LBBB. The PR interval following the next sinus impulse increases but remains shorter than the aforementioned long PR interval.Prolongation of the PR interval accompanying a change in BBB pattern indicates that the site of conduction delay is below the His bundle as the bundle branches are the only structures responsible for both the length of the PR interval and morphology of the QRS complex. 1,2 AV block No financial support was required.Address for reprints: Reginald T. Ho, M.D., in the setting of alternating BBB itself suggests block within the bundle branches although without His bundle recordings, intranodal and intra-Hisian block cannot be excluded. Therefore, PR prolongation preceding AV block during RBBB likely results from Wenckebach conduction over the left bundle (Fig. 2). In contrast, RB conduction after long pauses but its failure otherwise during sinus rhythm implies phase 3 block. In the presence of infra-Hisian AV block phase 3, RBBB alone cannot explain resumption of RB conduction after each pause because the proximal RB is always exposed to the sinus rate whether or not AV block is present. During LB Wenckebach left-toright transeptal conduction and late retrograde penetration of the RB maintains its refractoriness for each subsequent sinus impulse. When AV block occurs, momentary loss of the transeptal link allows recovery of RB excitability.The differential diagnosis of the LBBB QRS complexes terminating each pause include right ventricular escape complexes, ventricular preexcitation over a right-sided accessory pathway, and LBBB aberration. The smooth and rapid downstroke of the QRS complex in lead V1 argues strongly against a ventricular origin and favors aberration. 3 Perhaps the most likely explanation for the ...

Background: Transthoracic Echocardiography (TTE) is routinely performed in the setting of acute stroke and transient ischemic attack (TIA) to evaluate for a cardiac source of emboli. Although standard of care, guidelines remain ambiguous on the indications and recommendations for its routine use. Point-of-care ultrasound (POCUS), a quick bedside method of echocardiography using an easily portable, hand-held device, has been studied extensively in the ED, trauma, and ICU settings, but not for acute stroke and TIA. Here, we demonstrate the feasibility of using POCUS for the purpose of screening echocardiography in acute stroke & TIA patients. Additionally, we compare POCUS with TTE in order to evaluate the veracity of the point-of-care method with the gold standard. Methods: A retrospective comparison was made between routine TTE and POCUS results performed by a cardiologist during consultation. 99 patients were included, each admitted for workup of stroke, TIA, or retinal artery occlusions, and had a cardiology consultation for any reason. Parameters compared included left ventricular (LV) function, left atrial (LA) size, mitral valve (MV) and aortic valve (AV) pathology, and the presence of LA or LV thrombi, masses, or aneurysms. Results: All 16 cases with significant abnormalities (LV dysfunction, LV thrombi, or AV/MV vegetations) that were found on TTE were also identified by POCUS. Of the 13 patients with severely abnormal LV function on TTE, 12 were identified as severe on POCUS, and one as mild-moderate. Findings in 9 of these 16 patients led to a change in management, including one case where a large LV thrombus requiring a heparin infusion was identified hours earlier by POCUS. Conclusions: POCUS was comparable and non-inferior to the gold standard TTE for the purpose of screening echocardiography in the workup of acute ischemic stroke & TIA. Significant findings on TTE were all identified by a bedside POCUS (with the only discrepancy in the degree of LV dysfunction in a single case). All TTE findings resulting in management changes were also identified by POCUS. Importantly, POCUS can be used as a quick diagnostic screening tool to help establish an earlier diagnosis of life threatening conditions, and may lead to earlier management and treatment decisions.