Open-heart techniques and mitral valve plasty for mitral regurgitation in toy- and small-breed dogs: A review

Abstract

In human medicine, in the past, open-heart techniques for low-bodyweight children and newborn babies with congenital heart disease were more difficult than high-bodyweight adults. In toy- and small-breed dogs with mitral regurgitation (MR), an acquired heart disease, these techniques are more difficult to perform than for congenital heart diseases in young medium-sized or large dogs because of old age and low body weight. Therefore, improved open-heart techniques and mitral valve surgery for severe MR in older toy- and small-breed dogs are essential. Through our surface-cooling hypothermia (sHT) studies, we designed a new, improved open-heart method, namely, "the low-flow cardiopulmonary bypass (CPB) combined with deep sHT in toy- and small-breed dogs (Japan method)"; sHT was later replaced by blood-cooling hypothermia (bHT). At the same time, we devised a new, improved mitral valve plasty (MVP) applicable to severe MR, instead of mitral valve replacement, in toy- and small-breed dogs. This MVP technique was combined with artificial chordal reconstruction, semi-circular suture annuloplasty (AP), and direct scallop-suture valvuloplasty. These MVP techniques are simple, durable, and lead to good long-term quality of life in toy- and small-breed dogs. This review highlights the benefits of our improved CPB and MVP techniques (Japan method) for severe MR in toy-and small-breed dogs, which have led to a high success rate for MVP in severe clinical MR cases in Japan. It may further contribute to the development of more robust techniques for MR in toy- and small-breed dogs. This also represents the first comprehensive review of the history of open-heart surgery, CPB techniques, and MVP methods for MR in toy- and small-breed dogs.

Keywords: Direct scallop-suture valvuloplasty; Mitral regurgitation; Mitral valve plasty; Open-heart techniques; Toy and small dogs.

Fig. 1.. Diagram of the CPB circuit with a hemoconcentrator and access to the vessels and heart for left atriotomy (partially modified CPB circuit of Kanemoto et al., 2010). Unoxygenated blood is drained by gravity through a venous cannula in the LJV; the tip of the cannula is inserted into the RA, and the blood drains into the hard reservoir. A roller pump then returns the oxygenated blood to an arterial cannula in the LCA through a heat-exchanger and membrane oxygenator. In this CPB circuit, a hemoconcentrator is added to the ultrafiltration circuit to prevent excessive hemodilution by ultrafiltration of the same volume as that of the cardioplegic solution administered through the ARC. AO = aorta; PA = pulmonary artery; RV = right ventricle; LA = left atrium; LV = left ventricle; ACC = aortic cross clamp.

Fig. 2.. Anesthesia and pump record about 1 and half hours of ACC time during complex MVP performed for severe MR in a male mixed Chihuahua aged 10 years and 2 months and with a bodyweight of 6.1 kg (the same dog as described in Fig. 7). ACC time: 1 hour and 26 minutes, whole pump (CPB) time: 2 hours and 18 minutes, the lowest ET: 20.1°C, mean PF during ACC: 56.2 ml/kg/minutes, mean arterial pressure (AP) during ACC: 41.1 mmHg, extubating time from operation end: 3 hours and 20 minutes, heart rate (HR).

Fig. 3.. Anesthesia and pump record over 2 hours of the aortic cross clamp (ACC) time during multiple MVP performed for extra-severe MR in a male Cavalier King Charles Spaniel aged 11 years and 4 months and with a bodyweight of 8.4 kg. ACC time: 2 hours and 5 minutes, whole pump (CPB) time: 2 hours and 41 minutes, the lowest ET: 22°C, mean PF during ACC: 61.8 ml/kg/minutes, mean arterial pressure (AP) during ACC: 26.1 mmHg, extubating time from operation end: 3 hours.

Fig. 4.. Diagram showing each valvuloplasty (VP) method for each deformed valve leaflet. (A): Triangle resection VP: triangle resection and suturing of prolapsed A2-3 area for elongated chorda in the anterior leaflet (AL). (B): Rectangular resection VP: rectangular resection and suturing of the prolapsed P2 scallop in the posterior leaflet (PL). (C): Direct scallop-suture (SS) VP: direct suturing of each prolapsed scallop (P1-P2, P2-P3) with deep gaps in the PL resulting in three damaged scallops sutured to one posterior leaflet (Kanemoto et al., 2017c).

Fig. 5.. Basic mitral valve plasty techniques (artificial chordal reconstruction and semi-circular suture annuloplasty) (cited from Kanemoto et al., 2017c). (A): Artificial chordal reconstruction (ACR): A preoperative diagram is shown on the left, and a perioperative diagram is shown on the right. (B): Semi-circular suture annuloplasty (SAP) (modified DeVega method). (AL): anterior leaflet (A1, A2, A3); (PL): posterior leaflet; (CH): chordae; (APM): anterior papillary muscle; (PPM): posterior papillary muscle.

Fig. 6.. Additional MVP techniques (direct SS VP method in the PL and commissural AP method in the AC in addition to the basic MVP (Fig. 5) (cited from Kanemoto et al., 2017c). The prolapsed P1 and P2 scallops in the PL were sutured directly using 6-0 Proline sutures (direct SSVP). Mattress sutures with a pair of pledgets are placed at the AC for localized residual regurgitation (Key method). AL = anterior leaflet; PL = posterior leaflet; PC = posterior commissure.

Fig. 7.. Mitral valve lesion site on the mitral valve map and MVP performed in a mixed Chihuahua with the most severe MR (the same dog as described in Fig. 2) (cited from Yokoyama et al., 2017). (A) A1, A2, and A3 in the AL contact to P1, P2, and P3 in the PL, as shown in the mitral valve map. Black diamond shapes show two prolapsed chordae due to elongation in A1-2 and A2-3 in the AL. Red round shapes show four ruptured chordae in P1, P2, and P3 in the PL. Black margins of the AL and PL are remarkably hypertrophied. (B) Red lines show four ACRs performed in A1-2 and A2-3 chordae in the AL, and P1-2 and P2-3 chordae in the PL. Blue lines show three direct SS VPs performed in P1-P2, P2-P3 scallops, P3-PC scallop and leaflet with deep gaps in the PL, thus fixing all scallops in one leaflet. Brown dotted lines show SAP performed with alternately suturing from the anterior to the posterior base in the AL through the fibrous annulus of the PL. (C) (At the top middle part of Fig. 7B): Two PTFE sutures with triple-tying in the center and attached to a pledget are previously prepared. AL = anterior leaflet; PL = posterior leaflet; PC = posterior commissure leaflet; ACR = artificial chordal reconstruction; VP = valvuloplasty.