Tan, Nicholas Y.

Background: Rigorous study of ventricular fibrillation (VF) is not feasible in humans. The spatiotemporal characteristics of prolonged VF remain undefined, limiting our understanding of this lethal rhythm. Methods: VF was mapped in 4 canines. The endocardial and epicardial left ventricle (LV) and right ventricle (RV) were sequentially mapped at 0 to 15, 15 to 30, 30 to 45, and 45 to 60 minutes post-induction. Ten consecutive beats were used to determine the average cycle length and regularity index of ventricular and His-Purkinje system signals in discrete regions during each time interval. Results: Average VF time was 58±12 minutes. The shortest ventricular cycle length was present in the RV apical region (70±10 msec) at 0 to 15 minutes and at 15 to 30 minutes (89±31 msec) and LV apical region at 45 to 60 minutes (242±163 msec). The His-Purkinje system cycle length was the shortest at the RV outflow tract (75±3 msec) at 0 to 15 minutes, RV inflow and free wall (89±12 msec) at 15 to 30 minutes, LV apical region (83±14 msec) at 30 to 45 minutes, and inferior and inferolateral LV (145±23 msec) at 45 to 60 minutes. Regularity index was the highest in the RV inflow and free wall (78%) at 0 to 15 minutes, RV apical region (86%) at 15 to 30 minutes, LV septum and epicardial anterior RV (80%) at 30 to 45 minutes, and anterior and anterolateral LV (75%) at 45 to 60 minutes. Conclusions: These data suggest significant regional changes in electrical activity throughout VF in canines. A transition of fastest electrical activity from RV to LV apical regions across VF was observed. These novel insights of the temporal and spatial changes of VF merit further evaluation in diseased hearts to assess for reproducibility of findings.

Abstract Background Despite safety communications from the Food and Drug Administration (FDA) regarding the outbreak of Mycobacterium chimaera infections (MCIs) from contaminated heater-cooler devices, new cases continue to be identified. Methods We retrospectively reviewed confirmed cases of MCI that were managed at Mayo Clinic sites (Arizona, Florida, and Minnesota) from 09/2015 to 01/2021. Clinical histories including prior cardiovascular surgery were recorded. Diagnostic workup including ophthalmologic examination, imaging, and laboratory testing was reviewed. Treatment and survival outcomes on follow-up were obtained. Results Twelve patients with MCI were included. All patients had aortic valve or graft replacement. Five patients had their surgical procedures following the 10/15/2015 FDA safety communication. The mean time from surgery to symptom onset (range) was 32 (13–73) months. Ten of 11 patients who underwent ophthalmologic examination had chorioretinal abnormalities. Three patients who underwent microbial cell-free deoxyribonucleic acid sequencing tested positive for M. chimaera, which was subsequently confirmed with blood culture growth. Echocardiography and positron emission tomography/computed tomography (PET/CT) revealed evidence of prosthetic valve/graft infection in 7/12 (58.3%) and 6/10 (60.0%) of cases, respectively. Seven patients (58.3%) underwent redo cardiovascular surgery. Of these, 1 patient died 2 days postdischarge, 1 experienced spinal osteomyelitis relapse, and another had interval prosthetic valve fluorodeoxyglucose (FDG) uptake on PET/CT suspicious for recurrent infection. Among 4 patients on medical therapy only, 3 expired or transitioned to hospice during follow-up. Conclusions MCI continues to occur despite the FDA communications. Incorporation of ophthalmologic examination and use of advanced tools may improve MCI diagnosis. The mortality in these patients is high even with aggressive surgical/medical management.

Background: While NKX2-5 plays pivotal roles in human cardiac development and disease, no ChIP-Seq studies of NKX2-5 in human cardiac tissues currently exist, resulting in an incomplete understanding of its direct gene targets. Modern computational methods which identify binding sites using transcription factor motif and tissue-specific experimental data can help to fill this knowledge gap. Objective: To use computational methods to identify likely NKX2-5 binding sites and downstream gene targets using human heart-specific experimental data. Methods: Human cardiomyocyte DNAse hypersensitivity data (2 replicates) were downloaded from the Encyclopedia of DNA Elements (ENCODE) database. The position weight matrix (PWM) representing the transcription factor motif of NKX2-5 was obtained from JASPAR. We applied the Protein Interaction Quantification (PIQ) algorithm to detect NKX2-5 binding sites using the PWM and DNAse hypersensitivity data as inputs. RNA-Seq data from 108 human heart-specific samples (atrial appendages and left ventricles) were downloaded from the Genotype-Tissue Expression (GTEx) database. Protein-coding genes significantly expressed in the heart (RPKM <= 1 based on the GTEx RNA-Seq data) that were within 100kb of the predicted binding sites were then identified. Pathway analysis of these genes was performed using Ingenuity Pathway Analysis (IPA). Results: 1283 binding sites for NKX2-5 were discovered by PIQ. Of 12698 protein-coding, heart-expressed genes, 625 were within 100kb of these binding sites. The identified genes were highly enriched in physiologic categories like “Vasculogenesis” and “Development of Cardiovascular Tissue” (p = 2.36x10-9 and 2.31x10-8 respectively). Notable genes included: cardiac transcription factors (MEF2A, TBX20); growth factors (TGFB2, BMP2); muscle and ion channel function (ACTA2, BIN1), and; calcium signaling (CALM2, CAMK2D). Conclusion: By using computational analyses of transcription factor motif and human heart-specific experimental data, we have identified candidate downstream targets of NKX2-5. Future work will include validation studies in an external cohort and analysis of associations between these candidate genes and cardiac disease.

Introduction: Spontaneous coronary artery dissection (SCAD) is an uncommon but increasingly recognized cause of acute coronary syndrome and sudden cardiac death. We aim to review the occurrence of atrial fibrillation and atrial flutter in the Mayo Clinic SCAD Registry (MCSR) to gain insight into the association of SCAD and atrial arrhythmias. Methods: Atrial arrhythmias were queried amongst patients in the MCSR using diagnostic codes and text contained in both a large data repository known as the Advanced Cohort Explorer as well as a clinical database maintained by nurse abstractors for patients in the MCSR. All positive were manually verified using available medical records. Univariable logistic regression analysis was performed using JMP to investigate associations with classic cardiovascular risk factors. Results: A total of 1,215 patients from the Mayo SCAD registry were included. Six patients had a pre SCAD atrial arrhythmia, 19 had an atrial arrhythmia during a SCAD event, and 11 had a post SCAD atrial arrhythmia. Univariable analysis did not reveal significant associations with diabetes, hypertension, hyperlipidemia, or smoking. Conclusion: Atrial arrhythmias were not uncommonly seen in patients at the time of or after SCAD, especially after cardiac arrest or coronary artery bypass grafting. No significant associations with traditional cardiovascular risk factors were observed. Further investigation into the mechanism of atrial arrhythmia development as well as its management in the setting of SCAD is warranted.

Introduction: Mycobacterium Chimaera (MC) infections following cardiovascular surgery are challenging to diagnose given their insidious presentation. We therefore reviewed the various imaging modalities used to diagnose these infections at Mayo Clinic. Methods: Cases from 01/01/2010-06/01/2020 were identified using electronic medical records. Demographics and clinical history were collected. Imaging studies, including transthoracic echocardiogram (TTE), transesophageal echocardiogram (TEE), positron emission tomography / computed tomography (PET/CT), cardiac CT (CCT), and cardiac magnetic resonance (CMR) were reviewed. Results: A total of 7 patients (85.7% male) were found. 6 underwent aortic valve replacement and 1 received an aortic composite valve conduit. Surgical dates ranged from 01/2010-12/2018. Mean age at presentation was 63.3 years. Mean time from surgery to symptom onset was 28.0 months. All patients underwent TTE and TEE; prosthetic valve endocarditis was identified in 6 cases between both, while CMR established the diagnosis in 1 case. TTE showed prosthetic valve obstruction in 2 cases and an anterior pseudoaneurysm in 1 case. TEE findings included thickened prosthesis and/or vegetations (n=5), thickened posterior root (n=4), and root abscess (n=3). Among the 3 patients who underwent PET/CT, 2 demonstrated increased fluorodeoxyglucose (FDG) uptake around the aortic prosthesis; in addition, 1 had elevated FDG uptake in the myocardium suggesting myocarditis. 1 patient did not have aortic prosthesis FDG uptake. In the 2 patients who had CCT, 1 showed a pseudoaneurysm that prompted suspicion for endocarditis, and the other revealed a fluid collection adjacent to the aortic valve conduit. 2 patients underwent CMR; 1 had aortic prosthesis thickening and patchy areas of myocardial delayed enhancement suspicious for myocarditis, whereas the other showed vegetation and an aortic root abscess. Conclusion: TTE plus TEE successfully identified MC prosthetic valve endocarditis in most cases with TEE having higher specificity. Advanced imaging techniques are helpful to support the diagnosis and assess for myocardial and/or aortic involvement. Combining these modalities is therefore crucial in unveiling this elusive organism.

A 62-year-old man with metastatic hepatocellular carcinoma presented with ST elevation myocardial infarction had received one dose of nivolumab 3 weeks prior. Cardiac catheterisation was negative for obstructive coronary artery disease. He was transferred to the cardiac intensive care unit due to ventricular arrhythmias and markedly elevated troponin T levels. Transthoracic echocardiogram showed severely depressed left ventricular ejection fraction of 18% (normal 55%–70%) with mid and apical ballooning consistent with takotsubo syndrome (TTS). Intravenous glucocorticoids were administered due to suspicion for superimposed myocarditis. Cardiac MRI 3 days later showed mid-myocardial and subepicardial delayed enhancement in the inferior and lateral walls as well as apex indicative of myopericarditis. He clinically improved on steroids and was discharged with outpatient follow-up. This case highlights major cardiac complications that may arise with immune checkpoint inhibitor therapy. In addition, it emphasises the importance of assessing for concomitant myocarditis even when initial imaging suggests TTS.

Left bundle branch block may be due to conduction system degeneration or a reflection of myocardial pathology. Left bundle branch block may also develop following aortic valve disease or cardiac procedures. Patients with heart failure with reduced ejection fraction and left bundle branch block may respond positively to cardiac resynchronization therapy. Lead placement via the coronary sinus is the mainstay approach of cardiac resynchronization therapy. However, other options, including physiological pacing, are being explored. In this review, we summarize the salient pathophysiologic and clinical aspects of left bundle branch block, as well as current and future strategies for management.