Practice Update: Cardiology

ARRHYTHMIAS/HEART RHYTHM DISORDERS 25

an electrocardiogram is done is a likely predictor for most car- diac outcomes. Similarly, the finding of unanticipated sagittal sinus thrombosis on a CT scan or MRI will likely predict serious neurological sequelae, again because CT scans of the head are ordered in a subset of patients at risk for neurological events. In their study, however, the authors analyzed data from the Cardio- vascular Health Study (5577 participants) for a median of 12 years of the primary cohort, and the Atherosclerosis Risk in Communities Study (15,792 participants) for a median of 22 years as their rep- lication cohort. Thus, by design, ascertainment bias is essentially excluded and gives us reason to seriously examine the impact of their findings in terms of pathophysiology and population-wide screening. PACs and AF Paroxysmal AF often has discreet triggers that may manifest as single PACs, bigeminy, couplets, or paroxysmal monomorphic atrial tachycardia in addition to recorded AF. From their study, we can- not glean whether the associated AF in patients with recorded single PACs is paroxysmal or persistent. Furthermore, the loca- tion of origin of the PACs, coupling interval, and whether or not the absence of PACs on multiple electrocardiograms predicts freedom from AF are unknown. Given the very high likelihood of recordable AF in closely monitored patients with increasing age, a possibility that the patients in the cohort with PACs were other- wise at no higher risk for AF such as age, metabolic syndrome, sleep apnea, etc is unclear. PVCs and Congestive Heart Failure Frequent PVCs as a possible sole cause for cardiomyopathy is now well-established. At the same time, ventricular dysfunction from many causes may present as or have associated PVCs. This chicken and egg conundrum between PVCs and cardiomyopa- thy is often difficult to solve, especially when multifocal PVCs are

present and detected after a cardiomyopathy was established. The present study suggests that the electrical manifestation of PVCs may well precede mechanical dysfunction (heart failure) either as an early marker or as a cause. Single-Lead Continuous Monitoring There has been a plethora of devices for home and continuous nonobtrusive cardiac monitoring. These vary from single-lead electrocardiograms, pulse recordings, heart rate variability from either of the two above, and similar devices that are integrated into clothing, wearable devices, etc. Premature beats do not require a 12-lead electrocardiogram to record and could easily be done from single-lead recordings, and, indeed, with fairly simple trans- forms and algorithms looking at pulse rate variability to diagnose, quantify, and monitor. In the context of this burgeoning group of devices and related technologies, the present study is timely and important to integrate in future algorithm development. The Issue of Death A very important and nonintuitive finding from this study is that a single premature beat, atrial or ventricular, is a marker of and associated with the subsequent increased likelihood of death. We cannot glean from this study and report whether the likeli- hood of death is directly related to AF or heart failure but likely presume this pathophysiological link. The link between AF and death has been elusive to establish when reduction of preventa- ble stroke and associated comorbidity is considered, and, further, the possible incremental risk of PVCs over ventricular dysfunc- tion alone with regard to cardiovascular mortality has also been challenging. The present study with further analysis and repro- duction from other cohorts may give us the answers that, in turn, will leave difficult to answer questions on how aggressively we need to monitor and intervene to prevent death when single pre- mature beats are found. Conclusion

A contemporary international leader – a teetotaler – was asked why he doesn’t drink alcohol. The question was posed as to why a single drink, particularly in a social context, could possibly be harmful. The leader who had bad family experiences with addiction and alcoholism replied, “You can’t have two drags without first having one!” Although a single premature beat may seem innocuous, the mechanisms that underlie the possibility of creating a single beat, particularly with a re-entrant mechanism, establishes the potential for repetitive manifestations of this building block producing both arrhythmia and mechanical dysfunction.

Dr Asirvatham is Consultant, Division of Cardiovascular Diseases and Internal Medicine, Division of Pediatric Cardiology, Professor of Medicine and

Pediatrics Mayo Clinic College of Medicine, Program Director EP Fellowship Program, Director of Strategic Collaborations Center for Innovation, Mayo Clinic, Rochester, Minnesota. Dr Kella is from the Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota.

VOL. 2 • NO. 2 • 2017