Long‐term Intrinsic Rhythm Evaluation in Dogs with Atrioventricular Block

Abstract

BackgroundAtrioventricular block (AVB) is a conduction abnormality along the atrioventricular node that, depending on etiology, may lead to different outcomes.ObjectivesTo evaluate variations of intrinsic rhythm (IR) in dogs that underwent pacemaker implantation (PMI).AnimalsMedical records of 92 dogs affected by 3rd degree atrioventricular block (3AVB), advanced 2nd degree AVB (2AVB), paroxysmal 3AVB, 2:1 2AVB, or 3AVB with atrial fibrillation (AF) were retrospectively reviewed.MethodThe patient IR was documented with telemetry on the day of 1 – (95% CI, 1–2), 33 – (95% CI, 28–35), 105 – (95%CI, 98–156), and 275 days (95%CI, 221–380) after PMI. According to AVB grade at different examinations, AVB was defined as progressed, regressed, or unchanged.ResultsIn 48 dogs, 3AVB remained unchanged, whereas in 7 it regressed. Eight cases of 2AVB progressed, 3 regressed and 2 remained unchanged. Eight cases of paroxysmal 3AVB progressed and 3 remained unchanged. Four dogs affected by 2:1 2AVB progressed, 2 regressed, and 1 remained unchanged. All cases with 3AVB with AF remained unchanged. Regression occurred within 30 days after PMI, whereas progression was documented at any time. Variations in IR were associated with type of AVB (P < .03) and time of follow‐up (P < .0001).Conclusions and clinical importanceThe degree of AVB assessed at the time of PMI should not be considered definitive because more than one‐third of the cases in this study either progressed or regressed. Additional studies would be necessary to elucidate possible causes for transient AVB in dogs.

Indications for permanent pacing in dogs and cats

“…In particular, paroxysmal third-degree AVB progressed to permanent thirddegree AVB and most cases of 2:1 second degree AVB also progressed to third-degree AVB [35]. These findings are not in agreement with human medicine, in which 2:1 second degree AVB is considered to be stable [123], but support the need for PM implantation in dogs affected by paroxysmal third-degree AVB and 2:1 s degree AVB [35].…”

“…In such cases, small, uncontrolled studies have shown an improvement in symptoms with normalization of the PQ interval with dual-chamber pacing (AV resynchronization therapy) [67]. In veterinary medicine, one study that analyzed long-term intrinsic rhythm in dogs with AV nodal conduction disturbances had proven that the majority of cases showed persistent or progressive AVB [35]. In particular, paroxysmal third-degree AVB progressed to permanent thirddegree AVB and most cases of 2:1 second degree AVB also progressed to third-degree AVB [35].…”

“…In veterinary medicine, one study that analyzed long-term intrinsic rhythm in dogs with AV nodal conduction disturbances had proven that the majority of cases showed persistent or progressive AVB [35]. In particular, paroxysmal third-degree AVB progressed to permanent thirddegree AVB and most cases of 2:1 second degree AVB also progressed to third-degree AVB [35]. These findings are not in agreement with human medicine, in which 2:1 second degree AVB is considered to be stable [123], but support the need for PM implantation in dogs affected by paroxysmal third-degree AVB and 2:1 s degree AVB [35].…”

“…The pathogenesis of transient AVB secondary to acute myocarditis implies the presence of myocardial interstitial edema, and a correlation between increased thickness of the edematous cardiac walls and severity of AVB has been described [34]. The same mechanism has been suspected in dogs, with unknown prevalence, as it has been documented that 13% of dogs presented with transient AV conduction disturbances [35]. Both experimental models and human patients with spontaneously occurring acute lymphocytic myocarditis very often present AVB that lasts a few days or, less frequently, 2e3 weeks, and then regresses completely during the convalescent stage of 2e4 weeks in 67%e96% of the patients [32e34, 36,37].…”

“…Both experimental models and human patients with spontaneously occurring acute lymphocytic myocarditis very often present AVB that lasts a few days or, less frequently, 2e3 weeks, and then regresses completely during the convalescent stage of 2e4 weeks in 67%e96% of the patients [32e34, 36,37]. In addition, one study reported regression of AVB with improvement recorded within one month from PM implantation in 13% of dogs [35]. In human beings, it has been reported that the prevalence of persistent AVB [34] and permanent PM implantation is required in these patients.…”