Plasma potassium concentration and cardiac repolarisation markers, Tpeak-Tend and Tpeak-Tend/QT, during and after exercise in healthy participants and in end-stage renal disease.

PURPOSE: The cardiac T-wave peak-to-end interval (Tpe) is thought to reflect dispersion in ventricular repolarisation, with abnormalities in Tpe associated with increased risk of arrhythmia. Extracellular K+ modulates cardiac repolarisation, and since arterial plasma K+ concentration ([K+]) rapidly increases during and declines following exercise, we investigated the relationship between [K+] and Tpe with exercise. METHODS: Serial ECGs (Tpe, Tpe/QT ratio) and [K+] were obtained from 8 healthy, normokalaemic volunteers and 22 patients with end-stage renal disease (ESRD), at rest, during, and after exhaustive exercise. RESULTS: Post-exercise [K+] nadir was 3.1 ± 0.1, 5.0 ± 0.2 and 4.0 ± 0.1 mmol.L-1 (mean ± SEM) for healthy participants and ESRD patients before and after haemodialysis, respectively. In healthy participants, compared to pre-exercise, recovery-induced low [K+] was associated with a prolongation of Tpe (110 ± 8 vs. 87 ± 5 ms, respectively, p = 0.03) and an increase in Tpe/QT ratio (0.28 ± 0.01 vs. 0.23 ± 0.01, respectively, p = 0.01). Analyses of serial data revealed [K+] as a predictor of Tpe in healthy participants (ß = -0.54 ±0.05, p < 0.0001), in ESRD patients (ß = -0.75 ± 0.06, p < 0.0001) and for all data pooled (ß = -0.61 ± 0.04, p < 0.0001). The [K+] was also a predictor of Tpe/QT ratio in healthy participants and ESRD patients. CONCLUSIONS: Tpe and Tpe/QT ratio are predicted by [K+] during exercise. Low [K+] during recovery from exercise was associated with increased Tpe and Tpe/QT, indicating accentuated dispersion of ventricular repolarisation. The findings suggest that variations in [K+] with physical exertion may unmask electrophysiological vulnerabilities to arrhythmia.

Interference by Modern Smartphones and Accessories with Cardiac Pacemakers and Defibrillators.

PURPOSE OF REVIEW: The risk of cardiac implantable electronic device (CIED) interference from cell phones was previously thought to be low based on older studies. Current generation of smartphones have incorporated more magnets for optimization of wireless charging, attachment of accessories, and convenience functionalities. These magnets have the potential to cause CIEDs to inadvertently revert into magnet mode. The purpose of this review is to summarize recent findings on smartphones and their accessories causing interference on CIEDs. RECENT FINDINGS: Recent reports have demonstrated that the iPhone 12 series and accessories have the capability to cause CIED magnetic interference. Current generation of smartphones, smartwatches, wireless headphones, and accessories have the potential to cause CIEDs to revert into magnet mode in both in vivo and ex vivo experiments. The risk of a clinically significant event is unlikely as long as the Food and Drug Administration (FDA) recommendations are followed; keeping smartphones and accessories at least six inches away from CIEDs.

Real-life Clinical Outcomes of Low-voltage Isolation and Spatiotemporal Dispersion Ablation Strategies for Persistent Atrial Fibrillation.

Multiple techniques have been developed in addition to pulmonary vein isolation (PVI) to improve the outcomes of catheter ablation in patients with persistent atrial fibrillation (AF). We sought to evaluate the long-term efficacy of alternative techniques used in our laboratory for the treatment of persistent AF, including spatiotemporal dispersion (SD) and low-voltage isolation (LVI). Consecutive patients with persistent AF who underwent catheter ablation with the studied techniques between July 2016 and December 2019 were included in the study. PVI alone was compared with PVI plus SD and PVI plus LVI in terms of long-term freedom from atrial tachycardia (AT) and AF recurrence. Follow-up data were obtained from clinical records and hospital visits, which included a 7-day Holter monitor and electrocardiograms. The study was approved by the institutional review board of Rhode Island Hospital. A total of 382 patients underwent catheter ablation at our institution during the study period. One hundred seventy-two patients had paroxysmal AF and were excluded from the study. The remaining 210 patients had persistent AF and were included in the study. One hundred and three patients underwent PVI alone, while 48 had the addition of LVI and 59 had SD. Additionally, freedom from AT/AF recurrence at 18 months was 68% in the group that underwent LVI, 49% in the SD group, and 40% in the group that underwent PVI alone (log-rank P = .014). Freedom from AF recurrence was 74% in the LVI group, 71% in the SD group, and 43% in the PVI-alone group (log-rank P = .002). On multivariate Cox regression, LVI and left atrial size were found to be independent predictors of recurrence (hazard ratio, 0.39; 95% confidence interval, 0.206-0.760; P = .005 and hazard ratio, 1.4; 95% confidence interval, 1.105-1.923; P = .008, respectively). LVI and SD in addition to PVI were associated with greater freedom from AT/AF recurrence at 18 months compared to PVI alone.

A 34-Year-Old Woman with Third-Degree Heart Block and Atrial Flutter Associated with Lyme Carditis: A Case Report.

BACKGROUND Lyme disease is a tick-borne illness caused by bacteria of the Borrelia genus, endemic to the northeastern region of the United States. It typically presents with fevers, myalgias, and erythema migrans, but it can result in disseminated symptoms if left untreated. Lyme carditis is a rare, but potentially fatal complication of Lyme disease, occurring in up to 4-10% of untreated cases. Typically, it presents with atrioventricular conduction abnormalities, which resolve with intravenous antibiotics and temporary pacing if indicated. Diverse cardiac pathology, however, has been associated with Lyme carditis, which may be underrecognized in practice. CASE REPORT A 34-year-old woman with no significant medical history presented with fatigue, dizziness, and shortness of breath, 2 weeks after camping in Rhode Island. Her presenting electrocardiogram demonstrated third-degree heart block. She was noted to have targetoid rashes on her left shoulder and breast on physical examination. On laboratory work-up, she was found to have positive Lyme total antibody enzyme immunoassay and positive Lyme western immunoblot. The findings were diagnostic for Lyme carditis. The patient's cardiac rhythm subsequently converted to slow atrial flutter with variable ventricular response unresponsive to antibiotic therapy. Given evidence suggesting that atrioventricular conduction was preserved, synchronized electrical cardioversion was pursued and was ultimately successful in rhythm conversion to normal sinus rhythm. CONCLUSIONS Although Lyme carditis is rare, this diagnosis should be of high clinical consideration in presentations of cardiac conduction abnormalities with acute onset and without other obvious cause, particularly in Lyme-endemic regions such as the northeastern United States.

Atrial Na,K-ATPase increase and potassium dysregulation accentuate the risk of postoperative atrial fibrillation.

BACKGROUND: Postoperative atrial fibrillation is a common complication to cardiac surgery. Na,K-ATPase is of major importance for the resting membrane potential and action potential. The purpose of the present study was to evaluate the importance of Na,K-ATPase concentrations in human atrial biopsies and plasma potassium concentrations for the development of atrial fibrillation. METHODS: Atrial myocardial biopsies were obtained from 67 patients undergoing open chest cardiac surgery. Na,K-ATPase was quantified using vanadate-facilitated 3H-ouabain binding. Plasma potassium concentration was measured with ion-selective electrode. RESULTS: In patients with preoperative sinus rhythm, 3H-ouabain-binding site concentration was 16% higher in patients developing postoperative atrial fibrillation compared to patients maintaining sinus rhythm [302 +/- 15 pmol/g wet weight (n = 20) vs. 261 +/- 11 mmol/g wet weight (n = 33), p = 0.03]. Also with multivariable analysis, 3H-ouabain-binding site concentration was significantly associated with the development of atrial fibrillation. High increase in plasma potassium concentration during the perioperative period and surgery was associated with postoperative atrial fibrillation. CONCLUSIONS: The present study supports the increasing evidence of dysregulation of the potassium homeostasis as an important factor in the development of cardiac arrhythmias. High atrial Na,K-ATPase and sudden plasma potassium concentration increase may contribute to precipitate atrial fibrillation.

Premature ventricular contraction-induced cardiomyopathy: an emerging entity.

INTRODUCTION: Over the past 10-15 years, there has been an increasing amount of evidence that frequent premature ventricular contractions (PVCs) are associated with the development of a reversible cardiomyopathy. Areas covered: This review considers current evidence of the association between PVCs and the development of cardiomyopathy, risk factors, and available treatment modalities based on available published literature. Expert commentary: The field is rapidly evolving, although evidence is based primarily on observational studies. Pharmacological therapy may suppress PVCs and lead to resolution of cardiomyopathy in many patients. In addition, catheter ablation has emerged as an effective treatment modality that has compared favorably to pharmacological antiarrhythmic therapy. The excellent outcome in successfully treated patients should prompt physicians to consider whether frequent PVCs may be a contributing factor in patients with heart failure.

Potassium dynamics are attenuated in hyperkalemia and a determinant of QT adaptation in exercising hemodialysis patients.

Disturbances in plasma potassium concentration (pK) are well known risk factors for the development of cardiac arrhythmia. The aims of the present study were to evaluate the effect of hemodialysis on exercise pK dynamics and QT hysteresis, and whether QT hysteresis is associated with the pK decrease following exercise. Twenty-two end-stage renal disease patients exercised on a cycle ergometer with incremental work load before and after hemodialysis. ECG was recorded and pK was measured during exercise and recovery. During exercise, pK increased from 5.1 ± 0.2 to 6.1 ± 0.2 mM (mean ± SE; P < 0.0001) before hemodialysis and from 3.8 ± 0.1 to 5.1 ± 0.1 mM (P < 0.0001) after hemodialysis. After 2 min of recovery, pK had decreased to 5.0 ± 0.2 mM and 4.1 ± 0.1 mM (P < 0.0001) before and after hemodialysis, respectively. pK increase during exercise was accentuated after hemodialysis. The pK increase was negatively linearly correlated with pK before exercise (ß = -0.21, R(2) = 0.23, P = 0.001). QT hysteresis was negatively linearly correlated with the decrease in pK during recovery (ß = -28 ms/mM, R(2) = 0.36, P = 0.006). Thus, during recovery, low pK was associated with relatively longer QT interval. In conclusion, new major findings are an accentuated increase in pK during exercise after hemodialysis, an attenuated increase in pK in hyperkalemia, and an association between pK and QT interval adaptation during recovery. The acute pK shift after exercise may modulate QT interval adaptation and trigger cardiac arrhythmias.

Protection against ß adrenoceptor agonist reduction of plasma potassium in severe but not in moderate hypokalemia.

K-depleted and control rats were anesthetized and infused with terbutalin. In controls, plasma K concentration (pK) decreased by 0.7 mm (P = 0.01). In moderate hypokalemia terbutalin-induced decrease in pK was reduced by 0.3 mm for each 1 mm decrease in pK (n = 8, R(2) = 0.82, P = 0.002) and by 0.2 mm for each 10 mmol/g wet wt. decrease in muscle K content (n = 8, R(2) = 0.66, P = 0.01). Hence, for baseline pK of 4, 3 and 2 mm, decrease in pK was 0.7, 0.4 and 0.1 mm, respectively. In severe hypokalemia (1.7 mm), terbutain induced no further reduction in pK. The combined infusion of insulin and terbutalin showed no additive effect. Normalization of pK by KCl infusion in severe hypokalemia immediately abolished protection against terbutalin induced further pK reduction. Hence, terbutalin clamped pK at around 4 mm, whereas it continued to increase to around 5 mm without terbutalin infusion. Major new findings are: Protection against terbutalin induced further reduction in pK in severe pre-existing hypokalemia (<2 mm) and blunted but nevertheless severe further reduction in pK in more moderate pre-existing hypokalemia; immediate abolishment of protection by normalization of pK; protection against additive reduction in pK by terbutalin and insulin in severe hypokalemia. It may be advisable to avoid hypokalemia when using ß adrenoceptor agonists and to maintain pK in the upper normal range if at the risk of arrhythmia.

Endocarditis at a tertiary hospital: reduced acute mortality but poor long term prognosis.

The outcome in 132 patients with infective endocarditis diagnosed in accordance with the Duke criteria at a tertiary hospital in Denmark in the period 1998-2000 is reported. The total in-hospital mortality was 15%. Indications are that in-hospital mortality over the last decade has been reduced by around a quarter. Mortality after 3 months was 17% (CI 29%), after 3 years 32% (CI 16-47%) and after 5 years 39% (CI 22-55%). This 5-years mortality was 5 times that of an age and gender matched background population. After follow-up for 5-8 y, mortality was highest for prosthetic valve endocarditis (63% vs. 39%, p = 0.05). Heart surgery was performed in 51% of the cases. Patients who underwent surgery had a lower mortality at follow-up (36% vs. 52%, p = 0.04). The 5-year mortality was 30% (CI 9-52%) for patients treated with surgery and 48% (CI 23-72%) for patients treated without surgery. In multivariable analysis surgery was not an independent predictor for lower long-term mortality. Surgery was however an independent predictor for lower intermediate-term mortality. It is concluded that surgery may be associated with lower short- and intermediate-term mortality, while the effect might decline in the long-term. High age, prosthetic valve endocarditis, and Staphylococcus aureus endocarditis were independent predictors for high mortality. Although improvements have occurred over recent years, infective endocarditis is still a high mortality disease.