Background: Spontaneous second degree AV block induced by exercise (Ex2AVB) is reportedly rare (N=14 for largest published case series) but can cause profound exercise intolerance.
Hypothesis: We sought to determine the frequency of Ex2AVB in our exercise testing practice and describe patient characteristics, details of the rest and exercise ECGs, and effect on HR and exercise tolerance.
Methods: We reviewed the Mayo Integrated Stress Center database for non-imaging tests performed 2006 through 2010. All tests coded as “exercise induced second degree AV block” were captured and reviewed through the Mayo medical record. Tests were excluded if there was evidence of second degree AV block at rest, if Ex2AVB occurred during atrial flutter or pacemaker Wenckebach, or if Ex2AVB could not be distinguished from non-conducted PACs. Rest and peak HR and functional aerobic capacity (FAC) were downloaded from the database.
Results: There were 40,715 tests performed during the study period. Definite Ex2AVB was found on only 17 tests (.042%) on 16 unique patients (4 women, 12 men) aged 62 ± 17, range of 32 – 83 years. Rest HR was 76 ± 18 bpm, peak HR 107 ± 38 bpm or 69 ± 28% predicted. HR reserve ranged from -16 to +79 bpm, and 3 patients had a HR reserve < 0. FAC averaged 73 ± 22%. 1st degree AV block was found on 7 of the rest ECGs, and 6 patients were taking HR lowering drugs. Ex2AVB presented as Mobitz II in 14 cases, Mobitz I in 2. In 5 cases, Ex2AVB occurred only in recovery. Underlying congenital heart disease was identified in 4 patients, coronary disease in 5, 1 with adult degenerative valve disease, 1 with adult aortic disease, 5 without structural/known disease. Two patients had pacemakers (1 AICD), and 1 patient had RF ablation at baseline. Ex2AVB was intermittent in 7 and persistent in 9 patients. Peak HR was higher in intermittent versus persistent Ex2AVB (126 ± 39 vs. 88 ± 28, P < .01), as was FAC (87 ± 20 vs. 59 ± 14%, P < .01). Four patients with persistent Ex2AVB received PPM and 1 underwent PPM adjustment.
Conclusions: Ex2AVB is quite uncommon but can lead to significant exercise intolerance leading to PPM implantation. We confirm that structural or ischemic heart disease and resting conduction abnormalities are common findings in Ex2AVB. When Ex2AVB is intermittent intervention is seldom required.