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Syncope, collapse, and intermittent weakness monitoring
PAG E 4
A D VA N C E S
to trigger the storage of the most recent ECG data into permanent memory.
SYNCOPE, COLLAPSE, AND INTERMITTENT WEAKNESS MONITORING Background Diagnosis of the cause of syncope, collapse, or intermittent weakness can be difficult because of many possible causes and the intermittent nature of the episodes. Possible causes of syncope or collapse include metabolic disturbances, neurologic abnormalities, or cardiorespiratory abnormalities. In the absence of evidence for metabolic abnormalities on routine blood work, the evaluation becomes focused on cardiovascular or neurologic causes. Complete neurologic work up may include thorough physical neurologic evaluation combined with magnetic resonance imaging or computed tomography of the brain and cerebral spinal fluid (CSF) analysis. These procedures require general anesthesia and can carry risks associated with anesthesia and the collection of CSF. Cardiac evaluation of syncopal patients typically includes complete physical examination, thoracic radiography, echocardiography, and electrocardiography (ECG). Some cases may also require cardiac event monitor electrocardiography or Holter monitor continuous electrocardiography. Holter monitors only record a short time period and may miss episodes of intermittent collapse. Event monitors have the advantage of being able to monitor the ECG for a longer duration. Both Holter and event monitors are relatively bulky and may physically hamper normal patient activity. More recently, implantable loop recorders (ILRs) have become available to provide longer-term ECG monitoring without the external bulk of the other monitors. Which ambulatory ECG recording is used is based on length of recording needed, availability, and cost. The Reveal® Plus Insertable Loop Recorder is an implantable device that records a single lead ECG via 2 electrodes. The monitor is implanted subcutaneously over the left apex of the heart. The device continuously records a digital ECG signal which is stored. If an event is witnessed, a remote activating device can be used
Objectives To retrospectively review the diagnosis and outcome of syncope or collapse in dogs that had an ILR recorder placed as part of the diagnostic evaluation.
Procedure Medical records of 23 client-owned dogs that were presented for evaluation of syncope, collapse, or intermittent weakness using an ILR recorder were retrospectively reviewed.
Results Recurrent syncope occurred in 13 of 23 dogs (57%), and a positive diagnosis of the cause of the event was made in 11 of 13 dogs. Six of the 11 dogs had prolonged periods of sinus arrest with slow ventricular escape rate. There was also one dog each with suboptimal fixed heart rate by endocardial pacing, high-grade, seconddegree atrioventricular block, supraventricular tachycardia, normal ECG during multiple episodes, and high-grade, seconddegree atrioventricular block or sinus arrest.
Author Conclusion The Reveal® Plus ILR device is successful in diagnosing a high percentage of cases of syncope, collapse, or intermittent weakness in the dog.
Inclusions Two figures, 12 references.
Editor Annotation This retrospective study increases the number of reports of the use of ILRs in dogs for diagnosis of arrhythmias. These devices have demonstrated their value in diagnosis of collapse in humans with intermittent and infrequent clinical signs, as they can often acquire data for up to 18 months after implantation. While this report demonstrated a diagnostic value similar to that of previous reports, the authors noted that none of the patients had routine Holter or event monitoring performed prior to implantation of the ILR. Therefore, it is not clear whether the more invasive procedure, with its associated anesthetic and perioperative risks (one dog developed an infection at the implantation site), provided a higher rate of diagnosis than more conser-
A D VA N C E S
vative and less invasive methods. It is possible that simple Holter monitoring or event monitoring would have provided a similar rate of diagnosis as the authors observed. The authors did mention that the median time to diagnosis was 42 days (6 weeks), with a range of 1 to 467 days. This would argue that many of these events occurred well beyond the time frame in which Holter or routine event monitoring would be able to make a diagnosis. However, the study would have been more convincing if the authors had exhausted more routine diagnostic procedures before implanting the ILR, or if they had reserved the ILR for cases that had demonstrated infrequent episodes. Clinicians should be aware of the potential for ILRs to aid in the diagnosis of infrequent episodic collapse, weakness, or apparent syncope. The authors failed to mention the costs associated with such devices, such as the need for anesthesia, surgery, and the cost of the device itself, all which are substantially greater than for routine Holter or event monitoring. Therefore, these devices should be reserved for cases in which the diagnosis is not achievable by routine diagnostics and in which a cardiac cause is strongly suspected. (MR) MacKie BA, Stepien RL, Kellihan HB. Retrospective analysis of an implantable loop recorder for evaluation of syncope, collapse, or intermittent weakness in 23 dogs (2004-2008). J Vet Cardiol 2010;12:25-33.
PAG E 5
A D VA N C E S
to trigger the storage of the most recent ECG data into permanent memory.
SYNCOPE, COLLAPSE, AND INTERMITTENT WEAKNESS MONITORING Background Diagnosis of the cause of syncope, collapse, or intermittent weakness can be difficult because of many possible causes and the intermittent nature of the episodes. Possible causes of syncope or collapse include metabolic disturbances, neurologic abnormalities, or cardiorespiratory abnormalities. In the absence of evidence for metabolic abnormalities on routine blood work, the evaluation becomes focused on cardiovascular or neurologic causes. Complete neurologic work up may include thorough physical neurologic evaluation combined with magnetic resonance imaging or computed tomography of the brain and cerebral spinal fluid (CSF) analysis. These procedures require general anesthesia and can carry risks associated with anesthesia and the collection of CSF. Cardiac evaluation of syncopal patients typically includes complete physical examination, thoracic radiography, echocardiography, and electrocardiography (ECG). Some cases may also require cardiac event monitor electrocardiography or Holter monitor continuous electrocardiography. Holter monitors only record a short time period and may miss episodes of intermittent collapse. Event monitors have the advantage of being able to monitor the ECG for a longer duration. Both Holter and event monitors are relatively bulky and may physically hamper normal patient activity. More recently, implantable loop recorders (ILRs) have become available to provide longer-term ECG monitoring without the external bulk of the other monitors. Which ambulatory ECG recording is used is based on length of recording needed, availability, and cost. The Reveal® Plus Insertable Loop Recorder is an implantable device that records a single lead ECG via 2 electrodes. The monitor is implanted subcutaneously over the left apex of the heart. The device continuously records a digital ECG signal which is stored. If an event is witnessed, a remote activating device can be used
Objectives To retrospectively review the diagnosis and outcome of syncope or collapse in dogs that had an ILR recorder placed as part of the diagnostic evaluation.
Procedure Medical records of 23 client-owned dogs that were presented for evaluation of syncope, collapse, or intermittent weakness using an ILR recorder were retrospectively reviewed.
Results Recurrent syncope occurred in 13 of 23 dogs (57%), and a positive diagnosis of the cause of the event was made in 11 of 13 dogs. Six of the 11 dogs had prolonged periods of sinus arrest with slow ventricular escape rate. There was also one dog each with suboptimal fixed heart rate by endocardial pacing, high-grade, seconddegree atrioventricular block, supraventricular tachycardia, normal ECG during multiple episodes, and high-grade, seconddegree atrioventricular block or sinus arrest.
Author Conclusion The Reveal® Plus ILR device is successful in diagnosing a high percentage of cases of syncope, collapse, or intermittent weakness in the dog.
Inclusions Two figures, 12 references.
Editor Annotation This retrospective study increases the number of reports of the use of ILRs in dogs for diagnosis of arrhythmias. These devices have demonstrated their value in diagnosis of collapse in humans with intermittent and infrequent clinical signs, as they can often acquire data for up to 18 months after implantation. While this report demonstrated a diagnostic value similar to that of previous reports, the authors noted that none of the patients had routine Holter or event monitoring performed prior to implantation of the ILR. Therefore, it is not clear whether the more invasive procedure, with its associated anesthetic and perioperative risks (one dog developed an infection at the implantation site), provided a higher rate of diagnosis than more conser-
A D VA N C E S
vative and less invasive methods. It is possible that simple Holter monitoring or event monitoring would have provided a similar rate of diagnosis as the authors observed. The authors did mention that the median time to diagnosis was 42 days (6 weeks), with a range of 1 to 467 days. This would argue that many of these events occurred well beyond the time frame in which Holter or routine event monitoring would be able to make a diagnosis. However, the study would have been more convincing if the authors had exhausted more routine diagnostic procedures before implanting the ILR, or if they had reserved the ILR for cases that had demonstrated infrequent episodes. Clinicians should be aware of the potential for ILRs to aid in the diagnosis of infrequent episodic collapse, weakness, or apparent syncope. The authors failed to mention the costs associated with such devices, such as the need for anesthesia, surgery, and the cost of the device itself, all which are substantially greater than for routine Holter or event monitoring. Therefore, these devices should be reserved for cases in which the diagnosis is not achievable by routine diagnostics and in which a cardiac cause is strongly suspected. (MR) MacKie BA, Stepien RL, Kellihan HB. Retrospective analysis of an implantable loop recorder for evaluation of syncope, collapse, or intermittent weakness in 23 dogs (2004-2008). J Vet Cardiol 2010;12:25-33.
PAG E 5