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The CardioNerds Cardiology Case Reports series shines light on the hidden curriculum of medical storytelling. We learn together while discussing fascinating cases in this fun, engaging, and educational format. Each episode ends with an “Expert CardioNerd Perspectives & Review” (E-CPR) for a nuanced teaching from a content expert. We truly believe that hearing about a patient is the singular theme that unifies everyone at every level, from the student to the professor emeritus.

We are teaming up with the ACC FIT Section to use the #CNCR episodes to showcase CV education across the country in the era of virtual recruitment. As part of the recruitment series, each episode features fellows from a given program discussing and teaching about an interesting case as well as sharing what makes their hearts flutter about their fellowship training. The case discussion is followed by both an E-CPR segment and a message from the program director.

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Patient Summary

A male in his early 40s presented for second opinion regarding multiple ICD shocks. 10 years prior he was diagnosed with a “weak heart,” thought secondary to a viral illness and a dual-chamber ICD was placed at that time. He noted shocks occurring for the first time 5 years prior, at which time amiodarone was started. They recurred two years prior, when he was diagnosed with paroxysmal atrial fibrillation. Finally, he was hospitalized one month before presentation with multiple ICD shocks and was found to have high defibrillation thresholds (DFTs) and amiodarone was stopped. He  then presented for a second opinion from the Northwestern CardioNerds! 

The patient had been doing well on GDMT and had NYHA Class I symptoms (Enjoy Ep #13 – Approach to GDMT). He did note a family history of a cousin with “cardiac issues” and did not know his father’s family history. Physical exam demonstrated bradycardia and ECG demonstrated an a-paced, v-sensed rhythm at 50 bpm. TTE demonstrated a moderately dilated LV with LVEF 30%, globally reduced LV function and multiple wall motion abnormalities without a vascular distribution.  PET-CT was performed which showed diffuse uptake and high-intensity signal at the inferolateral and basal anterior walls. Cardiac MRI showed diffuse circumferential epicardial delayed enhancement with associated diffuse, enhancing thickening of the pericardium favoring inflammatory versus fibrotic process. Patient was initially diagnosed with cardiac sarcoid and started on prednisone and weekly methotrexate.  

On return of genetic testing, patient found to have a pathogenic variant for desmoplakin gene, and it was felt his cardiomyopathy was secondary to desmoplakin Left Dominant Arrhythmogenic Cardiomyopathy (LDAC, or left-dominant ARVC) presenting with inflammatory myocardial injury. On follow up the patient remained listed for transplant, and DFTs improved off amiodarone.  

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Episode Schematics & Teaching

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The CardioNerds 5! – 5 major takeaways from the #CNCR case

1. We started the case talking about DFTs. What are DFTs?! 
   • Defibrillation Thresholds (DFTs) are the minimal amount of energy required to return a patient to sinus rhythm that is in a cardiac dysrhythmia.  
   • Most modern ICD leads have thresholds less than 15 joules and typically less than 10 joules with biphasic shocks. High DFT thresholds tend to be defined as >25J or a safety margin of <10J. 
   • DFT testing is not routinely recommended during implantation of left-sided transvenous devices; however, in patients undergoing right-sided transvenous ICD or ICD pulse generator changes, DFT testing is a reasonable approach. Patients undergoing subcutaneous ICD placement should generally have DFT testing. 
   • Contraindications to DFT testing include acute LV thrombus, atrial fibrillation/flutter without adequate anticoagulation, severe aortic stenosis, recent stroke or TIA, or hemodynamic compromise as DFT itself can cause hypotension and/or CVA.   
     
2. What are the major causes of high DFTs? 
   • First there are myocardial factors. This includes pathology that affects the current density through the myocardium. Conditions like hypertrophic cardiomyopathy, inflammatory cardiomyopathy, or significant LV dilation can lead to high DFTs.    
   • The second set of factors are extra-cardiac causes that lead to increased impedance or resistance in the counter coil, such as high BMI or medications that lead to electrical imbalances such as amiodarone, which is a common cause of increased DFTs. However, the increase in DFT caused by amiodarone can be small and routine DFT testing in patients is not recommended.   
   • The last cause is a device factor, such as a lead fracture or a mal-positioned lead.  
     
3. In the case, we used MRI and PET. What are their role in Cardiomyopathy? 
   • Cardiac MRI (CMR) has transformed our ability to assess cardiomyopathies, specifically by accurately defining chamber size & function, characterizing myocardial tissue, and determining ischemia & viability. The specific pattern of late gadolinium enhancement (LGE) can help us differentiate between ischemic and non-ischemic etiologies and specific cardiomyopathies have characteristic patterns on MRI. Further, MRI can reliably identify edema, inflammation, and fatty replacement. CMR can provide a wealth of information in a variety of disease processes. Enjoy Ep #33 – CMR!
   • When evaluating an unexplained cardiomyopathy, FDG-PET can be useful in identifying active myocardial inflammation. 18F-FDG is a glucose analogue that can differentiate activated macrophages in areas of inflammation from normal myocytes if there is appropriate suppression of normal physiologic myocardial glucose uptake (I.e., Ketogenic Diet). This can be especially useful in Cardiac Sarcoidosis. Note, if there is global myocardial uptake, without diffuse perfusion defects, it may be a false positive scan in the setting of inadequate prep!  
   • For more on evaluation of heart failure, enjoy Ep #12 – Eval of New Onset HF & CPS Ep #48 – HFrEF. 
     
4. When should we consider a genetic cause to cardiomyopathy? 
   • If a family history suggests a genetic predisposition to cardiomyopathy, a cardiomyopathy seems out of proportion to an identified ischemic or non-ischemic cause, a patients presents with a cardiomyopathy at a young age, or if multi-modal imaging has not revealed a clear cause of a cardiomyopathy, genetic testing would be appropriate. 
   • Various studies have indicated that 30 to 50% of unexplained cases of (DCM) may have a genetic component. A detailed, at least three-generation family history should be obtained when initially evaluating a dilated CM, as most genetic cardiomyopathies are autosomal dominant with variable penetrance.  
   • Genetic counseling is key prior to genetic testing given complexities including interpretation of potentially confounding results and contextualizing results for relatives. 
     
5. Our patient’s final diagnosis was “Arrhythmogenic Desmoplakin Cardiomyopathy”…what’s that?! 
   • Arrhythmogenic RV Cardiomyopathy is a familial cardiomyopathy which usually affects the RV via fibrous or fibro-fatty replacement of normal myocardium. This predisposes patients to sudden cardiac death (SCD), ventricular arrhythmias, and heart failure.  
   • ARVC classically displays autosomal dominant inheritance from mutations in genes encoding desmosomal proteins affecting the cell-to-cell junction: desmoplakin (DSP), plakophilin 2 (PKP2), desmoglein 2 (DSG2), and desmocollin 2 (DSC2). Rarely, genes unrelated to cell-to-cell junction may be involved.  
   • Clinically we have noted a “Left-Dominant Arrhythmogenic Cardiomyopathy” (LDAC), with similarities to classic ARVC, but affecting predominantly the LV.  
   • Genotype-phenotype studies are shedding light on these “Arrhythmogenic Cardiomyopathies”. DSP mutations affect predominantly the LV (causing LDAC) whereas PKP2 mutations affect predominantly the RV (causing ARVC); these are distinct entities with key differences in presentation, progression, and markers of SCD risk (see Smith et al., Circulation 2020 reference for more!). Pertinent to our case, a subset of patients with DSP cardiomyopathy will have evidence of myocardial inflammation on FDG-PET and will are initially misdiagnosed as a myocarditis or sarcoidosis. 

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References

• Smith, E. D., Lakdawala, N. K., Papoutsidakis, N. et. al. (2020). Desmoplakin Cardiomyopathy, a Fibrotic and Inflammatory Form of Cardiomyopathy Distinct from Typical Dilated or Arrhythmogenic Right Ventricular Cardiomyopathy. Circulation. 141(23), 1872-1884 
• Crawford, T.C (2020). Desmoplakin Cardiomyopathy. https://www.acc.org/latest-in-cardiology/journal-scans/2020/06/11/15/43/desmoplakin-cardiomyopathy 
• Shulka, H. H., Flaker, G. C., Jayam, V. et. al. (2003). High defibrillation thresholds in transvenous biphasic implantable defibrillators: clinical predictors and prognostic implications. Pacing and clinical electrophysiology, 26(1p1), 44-48. 
• Russo, A. M., Sauer, W., Gerstenfeld, E. P., Hsia, H. H., Lin, D., Cooper, J. M., … & Patel, V. (2005). Defibrillation threshold testing: is it really necessary at the time of implantable cardioverter-defibrillator insertion?. Heart Rhythm, 2(5), 456-461. 
• Wilkoff, B. L., Fauchier, L., Stiles, M. K. et. al.(2016). 2015 HRS/EHRA/APHRS/SOLAECE expert consensus statement on optimal implantable cardioverter-defibrillator programming and testing. Ep Europace, 18(2), 159-183. 

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CardioNerds Case Reports: Recruitment Edition Series Production Team

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